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ambo embryology 1yr.ppt- health education

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Kedir Mohammed
Kedir Mohammed

medical resources

Health & Medicine
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Overview of Anatomy Anatomy – the study of the structure of body parts and their relationships to one another
Sub division of anatomy
1. Gross or macroscopic Study large body structures visible to the necked eye
2. Microscopic Study examination of body tissue using a microscope
2. Microscopic A. Cytology – study of the cell B. Histology – study of tissues
3. Other subdivisions
Embryology – study of developmental changes of the body before birth
9 He who sees things grow from the beginning will have the finest view of them. Aristotle, 384-322 BC
Developmental Periods Divide Prenatal (before birth) and Postnatal (after birth) periods 10
Embryology 11
Embryology  Embryology : – is the science which deals with the prenatal stage i.e. the intrauterine development of the human body till birth. 12
Teratology • (Gr. teratos, monster) • Is the division of embryology and pathology that deals with abnormal development (birth defects). • This branch of embryology is concerned with various genetic and/or environmental factors that disturb normal development and produce birth defects 13
Embryology 1.Prenatal period : a) Germinal period  Is the period from fertilization till formation of germ disk.  Its duration is about (18-21) days .  Safe period (non – sensitive to teratogenic agents ). 14
Embryology 1.Prenatal period : b) Embryonic period • is the period formation of germ disk till organogenesis . • its duration is from 4th week to 8th week . • Risk period (sensitive to teratogenic agents ). 15
Embryology 1. Prenatal period : C) Fetal period • is the period from organogenesis till birth. • during this period there are :- – Rapid body and organ growth . – The brain , ear , eyes , teeth , adrenal glands , the external genitalia continue development in this period . – There is a relative reduction of head growth compared to body growth . • less-safe period (less sensitive to teratogenic agents ) 16
Developmental period 2. Postnatal period (new born / off spring /neonate ): The changes occurring in the body after birth . 3. Gerology: The changes of body of old ages : 17
Embryology Types of Body cells 18
• A human being is formed of trillions of cells; these cells are of two types: A. Somatic cells- which are present in the whole tissues of the body B. Gametes which are the sperms and ova 19
A. Somatic cell • Each Som. C nucleus contain 46 chromosomes which are as follow • 22 pair of identical chromosome- autosomes • One pair of sex chromosomes which differ in the two sexes • 23,x 20
• The two chromosomes in each pair are called homologous chromosome • One is inherited from the mother and the other is from the father • Somatic cells are described as Diploid because their chromosomes are in homologus pair 21
Female somatic cell • The pair of sex chromosomes are identical and are called XX chromosomes. 22
Male somatic cells • The pair of sex chromosomes are quit different • One being long and is known as X chromosome • The other is much smaller and is known as Y 23
Homologous Chromosomes • Pair of chromosomes (maternal and paternal) that are similar in shape and size. • Homologous pairs (tetrads) carry genes controlling the same inherited traits. • Each locus (position of a gene) is in the same position on homologues. • Humans have 23 pairs of homologous chromosomes. 22 pairs of autosomes 1 pair of sex chromosomes
Homologous Chromosomes (because a homologous pair consists of 4 chromatids it is called a “Tetrad”) Paternal Maternal eye color locus eye color locus hair color locus hair color locus
Humans have 23 Sets of Homologous Chromosomes Each Homologous set is made up of 2 Homologues. Homologue Homologue
Autosomes (The Autosomes code for most of the offspring’s traits) In Humans the “Autosomes ” are sets 1 - 22
Sex Chromosomes The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male. XX chromosome - female XY chromosome - male In Humans the “Sex Chromosomes” are the 23rd set
Gamete (ovum or sperm) • Germ cell beyond a certain stage of development are haploid. • At fertilization one set of paternal (sperm) chromosomes unites with one set of maternal(egg) chromosomes, restoring the somatic cells that arise from it 29
• Although the two chromosomes of a homologous pair appear to be identical, they come from different parents and therefore are not genetically identical. 30
Sex Chromosomes The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male. XX chromosome - female XY chromosome - male In Humans the “Sex Chromosomes” are the 23rd set
Sex Chromosomes “Sex Chromosomes” …….the 23rd set 23 This person has 2 “X” chromosomes… and is a female.
33 Cell Type No. of chromosomes, Amount of DNA n Primordial germ cells n Spermatogonia n Oogonia n Zygote n Blastomeres n All normal somatic cells 46, 2n n Primary spermatocytes n Primary oocytes 46, 4n n Secondary spermatocytes n Secondary oocytes 23, 2n n Spermatid, spermatozoa n Mature oocytes (Ova) 23, n
Organization of the chromatin A human cell usually has 46 molecules of DNA with an average length of 44mm(total slightly over 2m) 34
• To put this in perspective, if a DNA molecule were the thickness of a telephone pole, it would reach about 4,400km into space-far higher than the orbits of satellites and spece shuttles. 35
• Imagine trying to make a pole 20cm thick and 4,400km long without breaking it!. The problem for a cell is even greater. 36
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3 Types of Cell Division • Amitosi- direct cell division-lower animal • Mitosis – ordinary somatic cell division – 2 daughter cells with identical chromosomes and genes to parents – Diploid cells – 2n chromosome complement • Meiosis – germline cell division – Results in formation of gametes – cells with only 23 chromosomes – Haploid cells – n chromosome complement 39
Mitosis • The somatic cells start their life as daughter cells after mitotic cell division. They then perform their specific functions till they divided again • An indirect cell division involving four phases prophase Metaphase Anaphase and Telophase followed by Interphase 40
INTERPHASE • The cell prepare itself for mitosis. • Nuclear membrane and nucleolus are very distinct. • Chromosomes appear like threads or filaments (chromatids). • Divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap) 41
Phases of Interphase • G1 (gap 1) – cell grows by producing proteins and cytoplasmic organelles • S (synthesis) – replication of the chromosomes • G2 (gap 2) – cell continue to grow and further protein synthesis occur 42
Cell Cycle of a Somatic Cell 1. Interphase 1. G1 2. S 3. G2 G1 + S + G2 phases = 16-24 h 2. Mitosis 43
The Cell Cycle G1 – Gap 1 (Lasts hours, days or years) – cell grows by producing proteins and cytoplasmic organelles – Occurs after mitosis and before S phase 44 end cells
The Cell Cycle • G0 phase Some cells may leave G1 stage permanently to perform their specialized functions, these cells are then called end cells – Resting stage/quiescent stage – Neurons, RBCs arrested in G1 = G0 phase – permanent G1 phase – Liver cells enter G0 but on damage  G1 and cell cycle continues 45
The Cell Cycle S phase – Stage of DNA synthesis – Each chromosome replicates  bipartite chromosome made up of sister chromatids – End of each chromatid marked by telomeres – specialized DNA sequences that ensure integrity of chromosomes during division – Sister chromatids held together at centromere – region of DNA associated with kinetochore – Provide a binding site for microtubules – DNA replication happens at thousands of origins of DNA replication – replication of the chromosomes 46
The Cell Cycle G2 phase – Gap 2 – A very short period – The cell is preparing for mitosis – Cell’s DNA doubled in S phase – Brief stage – cell continue to grow and further protein synthesis occur 47
Figure 17-31 Molecular Biology of the Cell (© Garland Science 2008) Centriole Replication • At a certain point in G1, the two centrioles of the pair separate. • During S phase, a daughter centriole begins to grow near the base of each mother centriole and at a right angle to it. • The elongation of the daughter centriole is usually completed by G2 48 centrosome
Mitosis • Mitosis: shortest of 4 stages • Important component: chromosomal segregation – process of distributing copy of each chromosome to each daughter cell • 5 stages: 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase 49
Mitosis is subdivided into prophase, prometaphase, metaphase, anaphase, and telophase • Prophase: Condensed chromosome start to become visible, Centrosomes start moving apart, Nucleolus starts disappearing • Prometaphase: Nuclear membrane breaks down • Metaphase: Chromosomes maximally condensed and align at the metaphase plate • Anaphase: The two sister chromatids separate and move toward opposite poles • Telophase: nucleus reassembly occurs, cytokinesis occurs 50
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Prophase • Condensation of chromosomes • Disintegration and disappearance of nucleolus • Formation of mitotic spindle – microtubule network 52 Prometaphase n Nuclear membrane breaks up n Congression occurs – chromosomes move to point midway between spindle poles n Condensation of chromosomes continue
Metaphase • Maximum condensation of chromosomes reached • Arranged at equatorial plane of cell • Balanced forces of microtubules from opposite poles at kinetochores 53
Anaphase • Begins when sister chromatids separate • Sister chromatids separate into daughter chromosomes • Daughter chromosomes move to opposite poles 54
Telophase and Cytokinesis • Telophase – Chromosomes decondense – Nuclear membrane reforms • Cytokinesis divides the cytoplasm – Cleavage begins as a slight indentation in cell surface deepens into a cleavage furrow. – Actin contractile ring and myosin motors drive the process – Cytoplasm cleaves separating daughter cells • Larger organelles, such as ER and Golgi, tend to fragment into small vesicles early in mitosis and then reassemble in daughter cells 55
Function of mitosis • Formation of a multicellular embryo from a fertilized egg • Tissue growth • Replacement of old and dead cells and • Repair of injured tissue • Egg and sperm are produced by a combination of mitosis and meiosis 56
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What if for gametogenesis • Sexual reproduction- bi-parental • If make a child-combined gamet • There must be a mechanism Keep chromosome number constant from generation to generation • 46 sperm chromosome 46 egg chro= 92+92=184 and forth 60
What if for gametogenesis • To prevent the chromosome number from doubling in every generation, the number is reduced by half during gametogenesis. 61
Meiosis • One round of DNA synthesis  2 rounds of chromosomal segregation – Meiosis I – reduction division – chromosome no. goes from diploid  haploid • Meiotic crossing over or recombination also occurs here: homologous segments of DNA exchanged between nonsister chromatids of pair of homologous chromosomes • Recombination important also for chromosome segregation – Meiosis II – like mitosis without a preceding DNA replication stage • Sister chromatids separate 62
Meiosis • Meiosis can convert one diploid cell into four haploid cells – Meiosis I: the first meiotic division – Homologous pairs join together to form a bivalent • Meiosis I produces two haploid cells that have chromosomes composed of sister chromatids – Unlike mitosis, in meiosis I, sister chromatids stay together. – Thus, the cells at the end of meiosis I are considered haploid because it contains only one of the two chromosomes of each bivalent – Genetic recombination 63
Meiosis I • Prophase I: Homologous chromosomes become paired and exchange DNA – Divided into 5 stages – Formation of synaptonemal complex and crossing-over occurs • Metaphase I: Bivalents align at the spindle equator – The kinetochores of sister chromatids lie side by side and face the same pole of the cell – Random orientation of maternal or paternal chromosomes – Chromosomes held together by chiasmata • Anaphase I: Homologous chromosomes move to opposite spindle poles • Telophase I and cytokinesis: Two haploid cells are produced 64
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Prophase I • Leptotene – chromatin begin to condense, 2 sister chromatids so close, cannot be distinguished • Zygotene – Homologs pair along entire length – synapsis – Chromosomes held together by synaptonemal complex • Pachytene – Synapsis complete, chromosome more tightly coiled – Chromosome appear bivalent – tetrad formation – Recombination takes place • Diplotene – Synaptonemal complex disappears – Bivalents begin to separate but held together at centromeres a– chiasmata • Diakinesis – stage of max condensation 66
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• The lateral elements of the synaptonemal complex start to attach to individual chromosomes during leptotene • The central element, which actually joins homologous chromosomes, does not form until zygotene • The formation of the synaptonemal complex is essential for recombination and for preventing aneuploidy 68
69 Bivalent Formation and Crossing-over
Anaphase I • Disjunction occurs – members of each bivalent move apart – HOMOLOGS (and usually alleles) SEPARATE!!! • Maternal and paternal chromosomes sort independently  223 combinations 70 Metaphase I n Nuclear membrane disappears n Spindle forms n Bivalents align at equator
Telophase I & Cytokinesis • Telophase I – 2 chromosome sets groups at opposite poles • Cytokinesis – cell divides into daughter cells  enter meiotic interphase (no DNA synthesis) – Spermatogenesis: equal – Oogenesis: secondary oocyte receives most cytoplasm, other cell  1st polar body 71
Meiosis II • Meiosis II resemble a mitotic division • Prophase II is very brief • Metaphase II – Kinetochores of sister chromatids now face in opposite directions • Anaphase II – Sister chromatids separate 72
Genetic Consequences of Meiosis • At the end of meiosis II there are four daughter cells, each containing a haploid set of chromosome – Reduction of chromosome number • Segregation of alleles • Random assortment of the homologues (law of independent assortment) – Meiosis generates genetic diversity – Over 8 million different combinations of chromosomes • Addition shuffling by crossing over • Nondisjunction refers to the failure of the two members of a homologous chromosome pair to separate during anaphase – Leads to aneuploidy diseases (trisomy 21-Down syndrome) 73
Comparison of Mitosis with Meiosis 74
75 Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 2 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction
Sexual reproduction • To reproduce sexually means that the parents must produce gametes(sex cell) that can meet and combine their genes in a Zygote(fertilized egg) 76
Embryology Gametogenesis (Formation of gametes ) Spermatogenesis=Formation of sperms (Male reproductive system) testis Oogenesis=Formation of Ova (Female reproductive system) ovary 77
Male genital system 1. The testis : Is the male sex gland . it lies in the scrotum suspended by the spermatic cord .it is enclosed by an isolated part of the coelomic membrane (the tunica vaginalis). The testis is divided into 250 compartments (lobes). Each containing (1-3)seminiferous tubules . The interstitial cells :produce the male sex hormone (testosterone). 78
Male genital system Male reproductive system 79
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Male genital system 2. Seminiferous tubules: (For formation of sperms) Seminiferous tubules contain 2 types of cells : • PGC----Spermatogonia (stem cells) – for production of sperms through process of spermatogenesis . • Sertoli cells (supporting cells): – Give nourishment to developing spermatids. – Give supporting to spermatogonia and spermatids. – Eat the excess parts of spermatids during spermiogenesis. 81
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Male genital system 3. Epididymis : – storage and maturation of sperms . – Adding two layers around the sperm (glycoprotein coat and seminal protein coat.) 84
Male genital system 4. The accessory glands : – Seminal vesicle : Secretes 60% of seminal fluid which contain fructose sugar (for nutrition). – Prostate gland :Secretes 20% of seminal fluid which contain bicarbonate for alkalization of acidic urine and give milky appearance of semen . – Cowper’s gland (bulbo-urethral gland) :Secretes 20% of seminal fluid which increase viscosity of the semen 85
Male genital system  Notes: Primordial germ cells (PGC): They are originated from the wall of the yolk sac at the end of 3rd week of embryonic development. These cells migrate by amoeboid movement from the yolk sac toward the developing gonads (primitive sex glands), where they arrive at the end of 4th week and invading the genital ridges in 6th week of development. PGC influence of development of the gonads into testes or ovaries . 86
Primordial germ cells Yolk sac The first human germ cells (primordial germ cells) appear in the wall of the yolk sac (3rd week) 87
The germ cells, through amoeboid movement, move towards the gonads where they arrive at about 5th week Primordial cells later differentiate into mature gametes i.e. spermatogonia (male) or oogonia (female) Primordial germ cells Yolk sac 88
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Spermatogenesis • Spermatogonia, which have been dormant in the seminiferous tubules of the testes since the fetal period, begin to increase in number at puberty. • After several mitotic divisions, the spermatogonia grow and undergo changes producing successive generations of cells . 90
Spermatogenesis • The newly formed cells can follow one of two paths: they can continue dividing as stem cells, also called type A spermatogonia, or they can differentiate during progressive mitotic cycles to become type B spermatogonia. 91
Spermatogenesis • Type B spermatogonia are progenitor cells that will differentiate into primary spermatocytes . • The primary spermatocyte has 46 (44 + XY) chromosomes and 4N of DNA. (N denotes either the haploid set of chromosomes [23 chromosomes in humans] or the amount of DNA in this set.) 92
Spermatogenesis • Soon after their formation, these cells enter the prophase of the first meiotic division. Because this prophase takes about 22 days, the majority of spermatocytes seen in sections will be in this phase. 93
Spermatogenesis • Each primary spermatocyte subsequently undergoes a reduction division-the first meiotic division-to form two haploid secondary spermatocytes, which are approximately half the size of primary spermatocytes. 94
• Subsequently, the secondary spermatocytes undergo a second meiotic division to form four haploid spermatids, which are approximately half the size of secondary spermatocytes. 95
• The meiotic process therefore results in the formation of cells with a haploid number of chromosomes. • With fertilization, the normal diploid number is again attained. 96
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Spermiogenesis – Spermiogenesis : is the final stage of production of spermatozoids. The spermatids are transformed into spermatozoa Definition : The process of transformation of spermatids into sperms. 100
Male genital system  Spermatogenesis : 2 n 2 n 2 n 2 n 2 n 2 n 2 n 2 n 2 n Multiplication Phase PGC Mitotic division Spermatogonia (B) Spermatogonia (A) 101
Male genital system  Spermatogenesis : Growth Phase Spermatogonia (B) Spermatogonia (A) Undergo growth Mitotic division reserve type 102
Male genital system  Spermatogenesis : Maturation Phase Undergo growth 2n n n Primary spermatocyte 1st meiotic division Secondary spermatocyte (2nd meiotic devision) 103
 Spermatogenesis : Spermiogenesis n n Secondary spermatocyte (2nd meiotic devision) n n n n Sperm 104
Spermiogenesis • Spermiogenesis is a complex process that includes 1. Formation of the acrosome (Gr. akron, extremity, + soma, body) 2. Condensation and elongation of the nucleus, 3. Development of the flagellum, and 4. Loss of much of the cytoplasm. 105
Spermiogenesis • Spermiogenesis can be divided into three phases. The Golgi Phase The Acrosomal Phase The Maturation Phase 106
Golgi phase • Prominent Golgi complex near the nucleus, mitochondria, a pair of centrioles, free ribosomes, and tubules of smooth endoplasmic reticulum. 107
• proacrosomal granules • acrosomal granule • acrosomal vesicle. • The centrioles • The flagellar axoneme 108
The Acrosomal Phase • The acrosomal vesicle spreads to cover the anterior half of the condensing nucleus and is then known as the acrosome • The acrosome contains several hydrolytic enzymes • dissociate cells of the corona radiata and • digest the zona pellucida, 109 hyaluronidase, neuraminidase, acid phosphatase, and a protease
The acrosome hyaluronidase, neuraminidase, acid phosphatase, and a protease that has trypsin-like activity 110
The Acrosomal Phase • One of the centrioles grows concomitantly, forming the flagellum. • Mitochondria aggregate around the proximal part of the flagellum, forming a thickened region known as the middle piece 111
The Maturation Phase • Residual cytoplasm is shed and phagocytosed by Sertoli cells, and • the spermatozoa are released into the lumen of the tubule 112
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Spermatogenesis • The end result is the mature spermatozoon, which is then released into the lumen of the seminiferous tubule 114
• Mature sperms are free-swimming, actively motile cells consisting of 115
The Sperm • The sperm consists of a head, neck, body and tail.  The head • The Head contains 2 main parts (the nucleus and the acrosome) both have two basic functions of the sperm (genetic and activating respectively ). – The nucleus occupies most of the available space of sperm head and its shape determines the shape of the head of the sperm. It contains only its haploid complement of DNA. – The acrosome contains hydrolytic enzymes as hyaluronidase and acrosine 116
The Sperm  Mid-piece • connected to head with a neck .(contain mitochondria ). 117
The Sperm  Tail • Its function is movement of the sperm to swim with head foremost . – The sperm cell is totally devoid of stored food (yolk) and protective envelope. it is also devoid of most cytoplasm organelles such as ribosomes and endoplasmic reticulum. 118
The Sperm 1 . Plasma membrane 2 . Outer acrosomal membrane 3 . Acrosome 4 . Inner acrosomal membrane 5 . Nucleus 6 . Proximal centriole 7 . Rest of the distal centriole 8 . Thick outer longitudinal fibers 9 . Mitochondrion 10. Axoneme 11. Anulus 12. Ring fibers A. Head B. Neck C. Mid piece D. Principal piece E. Endpiece Mature sperm 119
The Sperm  Semen  Source :  it is ejaculated during the male sexual act. It is composed from the fluids from the vas deferens , the seminal vesicles , the prostate gland and the Cowper’s gland . The major bulk of the semen is seminal vesicle fluid (60%)  The average ph is approximately 7.5 120
The Sperm  Semen  Content :  The usual quantity of semen ejaculated averages approximately 3.5 ml and in each ml. of semen is an average of 120 million sperms.  In normal persons , this number can vary from 35 millions to 200 millions . therefore an average of 400 million . Sperms are usually present in each ejaculate . When the number of sperms in each ml falls below approximately 20 million sperms , The person is likely to be infertile . 121
• Of the 200 to 300 million spermatozoa deposited in the vagina, only 300 to 500 reach the ovum • Only one sperm fertilizes the ovum. • Other spermatozoa aid the fertilizing sperm in penetrating the ovum barriers by their enzymes. • Only capacitated sperm pass freely through corona radiata 122
The Sperm  Transport of sperms – Sperms are non motile while they lie inside the male genital tract , but become motile after ejaculation in the vagina . By the undulating movement of their tails which act as propellers , The sperms ascend in the cervical canal and reach the cavity of the uterus . They are capable of swimming against the current produced by the cilia of the uterus . Few reach The uterine tubes where fertilization takes place . 123
The Sperm  Viability of sperms – The sperms discharged in the female genital tract can remain a live and motile . However , the period during which they are able to fertilize the egg (i.e. viable) is variable . It is believed that the sperms remain viable for (1-2)days only . Note :  Human sperms were preserved alive in vitro for 2 weeks . 124
The Sperm  Abnormalities of sperms  Numerical abnormalities a. Azo spermia (Aspermia ): No sperms at all , is found in the semen . b. Oligosperms : the number of sperms is few in the semen c. Necrospermia : the sperms are found dead 125
The Sperm  Abnormalities of sperms  Morphological abnormalities  The head and the tail may be abnormal , they may be: a. Giants b. Dwarfs c. Some times , sperms are joined in head or in tail d. No tail 126
The Sperm  Abnormalities of sperms  Sperms with morphological abnormalities lack motility and don’t fertilize the egg. 127
Embryology Gametogenesis (Formation of gametes ) Spermatogenesis=Formation of sperms (Male reproductive system) testis Oogenesis=Formation of Ova (Female reproductive system) ovary 128
The female reproductive system  The ovary:  Is the female sex gland . It lies in the ovarian fossa in the side wall of the pelvis . Its function is production of ova . It secretes two hormones: a. Estrogen (sex hormone): responsible for appearing of 2nd female sex characters . This hormone is secreted from Graffian follicle . b. Progesterone (pregnancy hormone):responsible for maintenance of pregnancy by increase the thickness and vascularity of uterine endometrium . This hormone is secreted from corpus luteum after ovulation process . 129
The female reproductive system  The uterus:  In which the fetus develop . It lies between the bladder anteriorly and the rectum posteriorly .  is a thick-walled, pear-shaped muscular organ averaging 7 to 8 cm in length, 5 to 7 cm in width at its superior part, and 2 to 3 cm in wall thickness  The uterus consists of two major parts .Body, the expanded superior two thirds Fundus Isthimus .Cervix, the cylindrical inferior one third Cervical canal Internal os External os 130
• The walls of the body of the uterus consist of three layers Perimetrium, the thin external layer Myometrium, the thick smooth muscle layer Endometrium, the thin internal layer 131
The perimetrium • is a peritoneal layer that is firmly attached to the myometrium. • outer serosa (connective tissue and mesothelium) or adventitia (connective tissue). 132
The Myometrium the thick smooth muscle layer 133
Endometrium • During the luteal (secretory) phase of the menstrual cycle, three layers of the endometrium can be distinguished microscopically : compact layer spongy layer basal layer 134
compact layer • A thin, compact layer consisting of densely packed, connective tissue around the necks of the uterine glands 135
spongy layer • A thick, spongy layer composed of edematous connective tissue containing the dilated, tortuous bodies of the uterine glands 136
basal layer • A thin, basal layer containing the blind ends of the uterine glands • At the peak of its development, the endometrium is 4 to 5 mm thick. • The basal layer of the endometrium has its own blood supply and is not sloughed off during menstruation. 137
functional layer • The compact and spongy layers, known collectively as the functional layer, disintegrate and are shed during menstruation and after parturition (delivery of a baby). 138
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The female reproductive system  Uterine (fallopian tube ): – In which fertilization , cleavage takes place . – It is lined with secretory epithelium for nourishment of ovum . – By its cilliary movement , muscle contraction help picking up of ovum from ovary . – approximately 10 cm long and 1 cm in diameter – extend laterally from the horns (L., cornua) of the uterus 141
Parts uterine tube the infundibulum, the ampulla, the isthmus, and the uterine part. 142
The female reproductive system Female reproductive system 143
Function of U.T • carry oocytes • Sperms (ampulla of the uterine tube ) • conveys the cleaving zygote to the uterine cavity. 144
OOGENESIS Oogenesis (ovogenesis) is the sequence of events by which oogonia are transformed into mature oocytes. • This maturation process begins before birth and is completed after puberty. • Oogenesis continues to menopause, which is permanent cessation of the menses (bleeding associated with the menstrual cycles). 145
OOGENESIS  Oogenesis : 2 n 2 n 2 n 2 n 2 n 2 n 2 n 2 n 2 n Multiplication Phase PGC Mitotic division 146
Stage of ooginesis 1. prenatal maturation 2. postnatal maturation 147
1. prenatal maturation • Around the end of the first month primordial germ cells migrates from the yolk sac to the gonadal primordia. • In the gonads these cells divide and transform into oogonia. 148
1. prenatal maturation • Division is so intense that • 2nd -600,000 oogonia, • 5th - >>>7 million. 149
Primordial germ cells Yolk sac 150
Primordial germ cells Yolk sac 151
1. prenatal maturation • During early fetal life(3rd month), oogonia proliferate by mitosis. • Oogonia enlarge to form primary oocytes before birth • As a primary oocyte forms, connective tissue cells surround it and form a single layer of flattened, follicular epithelial cells • The primary oocyte enclosed by this layer of cells constitutes a primordial follicle. 152
1. prenatal maturation • Primary oocytes begin the first meiotic division before birth. But instead of proceeding into metaphase They enter diplotene stage of of meiosis I. (Diplotene stage-resting stage during prophase) 153
1. prenatal maturation • The follicular cells (flat) are believed to secrete a substance, oocyte maturation inhibitor, which keeps the meiotic process of the oocyte arrested. Prophase The primary oocytes remain dormant in the ovarian follicles until puberty. 154
1. prenatal maturation By 7th.month • Majority of Oogonia (as well as primary oocytes) degenerate • Most of the Serviving Primary Oocytes (at prophase of meiosis I.) are individually surrounded by a layer of flat epithelial cells & form Primodial follicle (primary oocyte with a layer of flat epithelial cells) 155
Postnatal Maturation of Oocytes • As the primary oocyte enlarges during puberty, the follicular epithelial cells become cuboidal in shape and then columnar, forming a primary follicle. • The primary oocyte soon becomes surrounded by a covering of amorphous acellular glycoprotein material, the zona pellucida. • Scanning electron microscopy of the surface of the zona pellucida reveals a regular meshlike appearance with intricate fenestrations. 156
Postnatal Maturation of Oocytes • As a follicle matures, the primary oocyte increases in size and, shortly before ovulation, completes the first meiotic division to give rise to a secondary oocyte and the first polar body. • Unlike the corresponding stage of spermatogenesis, however, the division of cytoplasm is unequal. 157
Postnatal Maturation of Oocytes • The polar body is a small, nonfunctional cell that soon degenerates. • At ovulation, the nucleus of the secondary oocyte begins the second meiotic division, but progresses only to metaphase, when division is arrested. Zonar pellucida Secondary oocyte First polar body 158
Postnatal Maturation of Oocytes • primary oocytes in the ovaries • two million newborn • no more than 40,000 adolescence • Of these, only approximately 400 become secondary oocytes and are expelled at ovulation during the reproductive period. • Few of these oocytes, if any, are fertilized and become mature. 159
Postnatal Maturation of Oocytes • Beginning during puberty, usually one follicle matures each month and ovulation occurs 160
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The ovum  The ovum resembles any ordinary cell in its structure . It is large oval cell which varies from (117-142) μ in diameters . 162
The ovum  Coverings : a. 2 membranes :an inner thin delicate one called vitelline membrane and an outer thick transparent membrane called zona pellucida . b. Corona radiata: 2 or 3 layers of cells which surround the zona pellucida when the ovum is shed from follicle . 163
The ovum 164
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The ovum  Significance of egg membranes: a. provide the protection to the contents of egg b. Prevent polyspermia i.e. Fertilization by more than one sperm . c. Maintain the normal cleavage of the egg. 166
FEMALE REPRODUCTIVE CYCLES Commencing at puberty, females undergo reproductive cycles (sexual cycles), involving activities of the hypothalamus of the brain, pituitary gland (L., hypophysis), ovaries, uterus, uterine tubes, vagina, and mammary glands. • These monthly cycles prepare the reproductive system for pregnancy. 167
FEMALE REPRODUCTIVE CYCLES • Ovarian cycle • Time during which development of follicles, ovulation, and corpus luteum formation • Menstrual (endometrial) cycle • monthly changes in the internal layer of the uterus 168
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Hormonal changes At puberty & Ovarian cycle • Hypothalamus produces hormone • - gonadotropin releasing ( GnRH. ) • GnRH. Acts on Ant. Pituitary • Ant.Pit. --- Secretes FSH.& LH. • -these hormones stimulate & control cyclical changes in ovary • the Ovarian cycle started • -cyclical changes in ovary starting from the onset of puberty 171
172 LH
Hormones ( produced by Ant.Pituitary & Ovary) at Puberty Hypothalamus produces Gonadotropin-releasing hormone (GnRH)… Anterior Pituitary produces FSH. & LH. Ovary produces Fr.Follicular/ Theca cells Oestrogen Corpus luteum Progesterone 173
Ant.Pit. --- Secretes FSH.& LH. (FSH) stimulates the development of ovarian follicles and the production of estrogen by the follicular cells. (LH) serves as the "trigger" for ovulation (release of secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone. 174
OVARIAN CYCLE • FSH and LH produce cyclic changes in the ovaries-the ovarian cycle Which include A. development of follicles, B. ovulation and C. corpus luteum formation. 175
A. Follicular Development Development of an ovarian follicle is characterized by: - Growth and differentiation of primary oocyte - Proliferation of follicular cells - Formation of zona pellucida - Development of the theca folliculi 176
A. Follicular Development 1. primordial follicles—consist of a primary oocyte enveloped by a single layer of flattened follicular cells 177
A. Follicular Development 2. primary follicle Follicular cells divide by mitosis and form a single layer of cuboidal cells; the follicle is then called a unilaminar primary follicle Early primary follicle 178
A. Follicular Development • Follicular cells continue to proliferate and form a multilaminar primary or preantral follicle 179
A. Follicular Development • A thick amorphous layer, the zona pellucida, surrounds the oocyte. • Filopodia of follicular cells and microvilli of the oocyte penetrate the zona pellucida and make contact with one another via gap junctions. 180
A. Follicular Development 3. secondary or antral follicles Liquid (liquor folliculi) begins to accumulate between the follicular cells. The small spaces that contain this fluid coalesce, and the granulosa cells reorganize themselves to form a larger cavity, the antrum . • The follicles are then called secondary or antral follicles. Glycosaminoglycans, progesterone, androgens, and estrogens 181
A. Follicular Development • Cells concentrated at a certain point on the follicular wall forms a small hillock of cells, the cumulus oophorus, that protrudes toward the interior of the antrum and contains the oocyte . • A group of granulosa cells concentrates around the oocyte and forms the corona radiata. These granulosa cells accompany the oocyte when it leaves the ovary. 182
A. Follicular Development • the fibroblasts of the stroma immediately around the follicle differentiate to form the theca folliculi (theca from Greek, meaning box). • This layer subsequently differentiates into the theca interna and the theca externa 183
A. Follicular Development • The theca soon differentiates into two layers, an internal vascular and glandular layer, the theca interna, and a capsule-like layer, the theca externa. 184
A. Follicular Development • Thecal cells are thought to produce an angiogenesis factor that promotes growth of blood vessels in the theca interna, which provide nutritive support for follicular development. 185
A. Follicular Development • The dominant follicle may reach the most developed stage of follicular growth—the mature, preovulatory, or graafian follicle— and may ovulate. Preovulatory Graafian follicle 186
3. Pre-ovulatory stage i. formation of Graffian follicle about 37 hours b/f ovulation Antrum - enlarges considerably Oocyte -pushed to one side & embeded in a mound of cumulus oophorus Graffian Follicle -with antrum &-cumulus oophoricus 187
Maturation of Ovum in each cycle A. changes in Follicle -In each Cycle 15-20 Primodial follicles grow & pass thro’ i.Primary follicle(preantral) ii.Secondary follicle (antral) iii.Graafian follicle (preovulatory) but only One follicle b/c • Mature follicle • FSH. is necessary for maturation of Primary follicles to antral & preovulatory stages • LH.(increase in mid cycle) causes • i.secondary follicle to enter preovulatory stage • Secondary follicle grows rapidly to diameter of 25mm. Under the influence of FSH. & LH. Primodial follicle Primary follicle Secondary follicle antrum Graafia n follicle Granul osa cells zona pelucida Cumulus oophorus 188
A. Follicular Development • The early development of ovarian follicles is induced by FSH, but final stages of maturation require LH as well. • Growing follicles produce estrogen, 189
A. Follicular Development • Estrogen regulates development and function of the reproductive organs. • The vascular theca interna produces follicular fluid and some estrogen. Its cells also secrete androgens that pass to the follicular cells, which, in turn, convert them into estrogen. 190
Oocyte changes at preovulatory stage cont… • With a surge in LH matured follicle (usually one) enters • 3.Preovulatory stage B. formation of Secondary oocyte • -Primary oocyte (arrested in diplotene stage of 1st.meiotic division) enter metaphase (A) • (B) -Secondary oocyte is formed after completion of meiosis I. • (C) -Secondary oocyte enters meiosis II.(arrested at metaphase) Granulosa cells Secondary oocyte in meiosis ii. Primary oocyte in meiosis( I ). A Secondary oocyte & polar bdy 1 B C 191
B Ovulation • Defination • -process in which secondary oocyte is released from the ovary • Time of Ovulation • -14 day before next menstruation • (for woman with regular • 28 days cycle) 192
B Ovulation • Around midcycle, the ovarian follicle, under the influence of FSH and LH, undergoes a sudden growth spurt, producing a cystic swelling or bulge on the surface of the ovary. • A small avascular spot, the stigma, soon appears on this swelling. • Before ovulation, the secondary oocyte and some cells of the cumulus oophorus detach from the interior of the distended follicle. 193
Ovulation Surface bulge stigma 1.High level of estrogen to - hypothalamus & Ant.pituitary LH. surge Ovary Ovulation occurs 194 Ovulation is triggered by a surge of LH production. Ovulation usually follows the LH peak by 12 to 24 hours. The LH surge, elicited by the high estrogen level in the blood, appears to cause the stigma to balloon out, forming a vesicle. The stigma soon ruptures, expelling the secondary oocyte with the follicular fluid.
B Ovulation • The expelled secondary oocyte is surrounded by the zona pellucida and one or more layers of follicular cells, which are radially arranged as the corona radiata, forming the oocyte-cumulus complex. 195
B Ovulation • The LH surge also seems to induce resumption of the first meiotic division of the primary oocyte. • Hence, mature ovarian follicles contain secondary oocytes 196
C Corpus Luteum • Shortly after ovulation, Under LH influence, the walls of the ovarian follicle and theca folliculi collapse and are thrown into folds they develop into a glandular structure, the corpus luteum 197
corpus luteum secretes progesterone and  some estrogen, • causing the endometrial glands to secrete and prepare the endometrium for implantation of the blastocyst. 198
Type of corpus luteum 1. corpus luteum of pregnancy : 2 corpus luteum of menstruation 199
corpus luteum of pregnancy : 1. If the oocyte is fertilized, the corpus luteum enlarges to form a corpus luteum of pregnancy and increases its hormone production. • Degeneration is prevented by human chorionic gonadotropin. • 20 weeks of pregnancy. • the placenta 200
2. corpus luteum of menstruation no fertilization, the corpus luteum involutes and degenerates 10 to 12 days after ovulation. transformed into white scar tissue in the ovary, a corpus albicans. 201
Duration of ovarian cycle • Ovarian cycle persist • throughout the reproductive life of women and terminate at menopause, the permanent cessation of menstruation, usually between the ages of 48 and 55. • No ovarian cycle • during pregnancy • menopause 202
Menstrual (Endometrial) Cycle • is the time during which the oocyte matures, is ovulated, and enters the uterine tube. • The hormones produced by the ovarian follicles and corpus luteum (estrogen and progesterone) produce cyclic changes in the endometrium. 203
Menstrual (Endometrial) Cycle • The average menstrual cycle is 28 days, with day 1 of the cycle designated as the day on which menstrual flow begins 204
Phases of menstrual cycle 205 Menstrual Phase. Proliferative phase Luteal Phase 4 to 5 days 9 days 13 days
Phases of menstrual cycle 1. Menstrual Phase. (lasts 4 to 5 days) The functional layer of the uterine wall is sloughed off and discarded blood + endometrium= After menstruation, the eroded endometrium is thin. 206
Phases of menstrual cycle 2. Proliferative Phase. The proliferative (follicular, estrogenic) phase ~ 9 days coincides with growth of ovarian follicles and is controlled by estrogen secreted by these follicles. • two- to-three fold increase in the thickness of the endometrium and in its water content • Early during this phase, the surface epithelium reforms and covers the endometrium. • The glands increase in number and length, and the spiral arteries elongate. 207
Phases of menstrual cycle 3 Luteal Phase. The luteal (secretory, progesterone) phase, ~ 13 days, coincides with the formation, functioning, and growth of the corpus luteum. 208
Luteal phase • The progesterone produced by the corpus luteum stimulates the glandular epithelium to secrete a glycogen-rich material. • The glands become wide, tortuous, and saccular, and the endometrium thickens because of the influence of progesterone and estrogen from the corpus luteum and because of increased fluid in the connective tissue.. • As the spiral arteries grow into the superficial compact layer, they become increasingly coiled. • The venous network becomes complex and large lacunae (venous spaces) develop. • Direct arteriovenous anastomoses are prominent features of this stage 209
What happen to emdometrium cycle if 210
If fertilization does not occur • The corpus luteum degenerates.  Estrogen and progesterone levels fall and  The secretory endometrium enters an ischemic phase. • Menstruation occurs. 211
If fertilization occurs • Cleavage of the zygote and blastogenesis (formation of blastocyst) occur. • The blastocyst begins to implant on approximately the sixth day of the luteal phase (day 20 of a 28-day cycle). • Human chorionic gonadotropin, keeps the corpus luteum secreting estrogens and progesterone. • The luteal phase continues and menstruation does not occur. 212
TRANSPORTATION OF GAMETES 213
Oocyte transport Ovary to in infudibulum  The sweeping action of the fimbriae (move back and forth over the ovary) and  fluid currents produced by the cilia of the mucosal cells of the fimbriae "sweep" the secondary oocyte 214
Oocyte transport 215
TRANSPORTATION OF GAMETES • infudibulum to ampulla • peristalsis-movements of the wall of the tube characterized by alternate contraction and relaxation-that pass toward the uterus. 216
Oocyte transport i.fimbra sweep over the Ovary, & tube contracts ii.Oocyte with cumu pulled into the tube by fimbrae mment iii.Cilia sweep Oocyte • t/w Ut. • Note: • -cumulus lose contact • with oocyte once gets • in the tube 217
TRANSPORTATION OF GAMETES • Sperm Transport • In male reproductive tract • Epididymis The urethra The accessory sex produce secretions that are added to the sperm. • Ejaculated sperm • external os & the fornix of the vagina during sexual intercourse. 218
The reflex ejaculation of semen two phases: • Emission: • Epd-to-the prostatic part of the urethra ----peristalsis of the ductus deferens • Ejaculation • from the urethra through the external urethral orifice; this results from closure of the vesical sphincter at the neck of the bladder, contraction of urethral muscle, and contraction of the bulbospongiosus muscles. 219
Sperm Transport in FRT • external os ----cervical canal By movements of their tails. • Why against?????? • The enzyme vesiculase, produced by the seminal glands, coagulates some of the semen or ejaculate and forms a vaginal plug that may prevent the backflow of semen into the vagina. • When ovulation occurs, the cervical mucus increases in amount and becomes less viscid, making it more favorable for sperm transport. 220
Sperm Transport in In FRT • Cervical canal through the uterus to uterine tubes mainly from muscular contractions of the walls of these organs. • Prostaglandins in the semen • stimulate uterine motility at the time of intercourse and assist in the movement of sperms to the site of fertilization in the ampulla of the tube. • Fructose, secreted by the seminal glands, is an energy source for the sperms in the semen. 221
1. The volume of sperm or ejaculate (sperms suspended in secretions from accessory sex glands) averages 3.5 mL, with a range of 2 to 6 mL. 2. Mov’t speed 2-3 mm/min slow- in the acid environment of the vagina more rapid in the alkaline environment of the uterus 3. Duration 1. 5 minutes after their deposition near the external uterine os. 2. Some sperms, however, take as long as 45 minutes to complete the journey. 4. No of sperm that reach the Ampula Only approximately 200 sperms reach the fertilization site. Most sperms degenerate and are resorbed by the female genital tract. 222
MATURATION OF SPERMS • In most species, Freshy ejaculated spermatozoa are not capable of fertilization immediately upon entering the female reproductive tract • Sperm must undergo capacitation before they are fertilized Definition: • Morphologic, physiologic, and biochemical changes which occur to the sperm result in sperm capable of penetrating through the corona radiate and zona pellucid of the ovum. (removal of macro-molecular material from the sperm surface) 223
MATURATION OF SPERMS Freshy ejaculated sperm must undergo • a .Capacitation-utrus &FT • b .Acrosomal reaction • a. Capacitation • Definition - process in which changes occur in Sperm during its passage thro’female reproductive tract - Changes (during Capacitation) are. - removal of the following from plasma membr. - fr. Plasma membr.of Sperm overlying Acrosome - i. glycoprotein coat - ii. seminal plasma protein - Duration: - -last for about 7 hours 224
Capacitation of the sperm • Is a period of sperm conditioning in the female genital tract; mainly in the uterine tube & it takes about 7 hrs. • It entails epithelial interaction between the sperm and mucosal surface of the tube resulting in: - Removal of a glycoprotein coat and seminal plasma proteins from plasma membrane overlying the acrosomal region of spermatozoa. • Only capacitated sperm pass through corona cells & undergo acrosome reaction.
Effects of Capacitation on Sperm • Increased rate of metabolism • Flagellum beats more rapidly; Result: Sperm are more motile • Changes in sperm plasmalemma proteins allow sperm-egg binding and occurrence of the acrosome reaction • Pro-Acrosin (inactive) is converted to acrosin (active) • Sperm become capable of chemotaxis 226
b.Acrosomal reaction The acrosomal cap contains several enzymes like acid phosphatase, hyaluronidase, which are involved in penetration of the oocyte. Just before approaching the oocyte, the capacitated sperm head establishes multiple contacts and discharges the chemical substances in succession to overcome the barriers around the oocyte. This process of multiple contacts is known as acrosome reaction. Zona pellucida. Perivitellin e space Acrosom e 228
Acrosome contains 2 enzymes • Hyaluronidase (corona penetrating enzymes) Protein that breaks down mucopolysaccharides Mucopolysaccharides (hyaluronic acid) is the material that holds the cumulus oopherus cells together. • Acrosin This enzyme plus sperm flagellum aid in penetrating to the perivitelline space 229
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Note the following • Oocyte • It takes about 72 hours for an egg to reach the uterus • If it is to survive, an egg must be fertilixed within 12 to 24 hours for an egg to reach the uterus. • Therefore, in order to fertilize the egg before it dies, sperm must encounter it somewhere in the distal one-third of the uterine tube. 231
Sperm • spermatozoa can reach the distal uterine tube within 5-10minutes of ejaculation, but they cannot fertilize an egg for about 10hours. • most sperm are fertile for a maximum of 48hours after ejaculation, so there is little chance of ferilizing an egg if intercourse occurs more than 48 hours before ovulation 232
Viability of gametes • human oocytes are usually fertilized within 12 hours after ovulation(12-24hours). • Most human sperms probably do not survive for more than 48 hours in the female genital tract. 233
• Of the 200 to 300 million spermatozoa deposited in the vagina, only 300 to 500 reach the ovum • Only one sperm fertilizes the ovum. • Other spermatozoa aid the fertilizing sperm in penetrating the ovum barriers by their enzymes. • Only capacitated sperm pass freely through corona radiata 234
Viability of Oocyte &Spermatozoa • Oocyte after ovulation • -24 hours • Spermatozoa after ejaculation • -48 hours • (or may remain viable for several • days in female reproductive tract) • 3 days“Window” better chance for fertilization • b/t.2days b/f. & 1 day after Ovulation 235
Revision 1st week 236
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FERTILIZATION • Defnition • Fertilization is a complex sequence of coordinated molecular events that begins with contact between a sperm and an oocyte and ends with the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of the zygote, a unicellular embryo 240
site of fertilization 241
• -Ampullary region • -widest & (longest) • ampulla Ampulla Where does ferti. usually take place ? Why? Uterus Uterine tube 242
Zygote A zygote is a highly specialized, totipotent cell that marks the beginning of each of us as a unique individual. 243
zygote 244 The unicellular zygote divides many times and becomes progressively transformed into a multicellular human being through cell division, migration, growth, and differentiation.
Results of fertilization 1. Restoration of the diploid numbers of chromosomes half from the father and half from the mother . Hence the zygote contains a few combination of chromosomes different from both parents . 2. Determination of the sex of the new individual . An X-carrying sperm will produce a female (XX) embryo , and a Y – carrying sperm will produce a male (XY)embryo . Hence .the chromosomal sex of the embryo . is determined at fertilization.  Chromosome Y contains TDF (Testis determining factor ). 245
Results of fertilization 3. The characters , state of health or disease and the features derived father and mother are determined by fertilization and carried to the fetus . 4. Initiation of cleavage : without fertilization , The Oocyte usually degenerates 24 hours after ovulation. 246
Cleavage, Blastosis & Implantation 247
Cleavage Is a series of repeated mitotic divisions that results in an increase in the number of cells. 248
Result of cleavage 249
Cleavage • Zygote: • 2-cell stage • 4-cell stage • 8-cell stage • 16-cell stage (morula) Late blastocyst Early blastocyst trophoblasts cavity Inner cell mass morula 8 cells stage 2 cell stage 4 cell stage pellucida
Fig. 29.03
Site of cleavage 253
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Compaction After the nine-cell stage, the blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells 255
Importance of compaction Compaction permits greater cell-to-cell interaction and is a prerequisite for segregation 256
Blastocyst • When does morula • Enter Uterine cavity? • About 4 days aft.ferti. • Formation of Blastocyst • As the morula enters Ut.cavity(4 days) • fluid secreted by endometrial glands (uterine milk) enters morula • Fluid filled cavity- Blastocele • Morula b/c Blastocyst 4 days A. B. C. 257 Pass through zona pellucida
Formation of the blastocyst 258
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Blastomeres & derivatives What are the Blastomeres? What are their derivatives? Inner cell mass which will later gives rise to embryo K/s. Embryoblast Outer cell mass k/s-Trophoblast - placenta formation - Production of Human chorionic gonadotropin
Blastocyst cont.. • Zona pellucida,is it still necessary? • By 5th.day • A hole is formed in Z.pellucida (by an enzyme) • Blastocyst then squeezes thro’ the hole • rapidly increase in size • Now blastocyst (devoid of investments) is ready for Implantation •
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Implantation 263
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Formation of the hypoblast At approximately 7 days 265
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Chronology of Ovum (aft.Ovulation) 14th.day b/f next menstrua. Within 24Hrs.after Ovulation • 4 days after fertilization • 6th. Day after fertilzation • What happen to • -Blastomeres? • -Blastocele ? Day 5. Day 6.
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Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast Week Two Bilaminar Germ Disc Hypoblast
Day Eight – Bilaminar Disc Inner Cell Mass (embryoblast) Trophoblast Blastocele
Day Eight – Bilaminar Disc • Mitotic figures • Cells in the cytotrophoblast divide and migrate into the syncytiotrophoblast, where they fuse and lose their individual cell membranes.
Day Eight – Bilaminar Disc • Cells of the inner cell mass or embryoblast also differentiate into two layers: (a) a layer of small cuboidal cells the hypoblast layer; and (b) a layer of high columnar cells epiblast layer • Together, the layers form a flat disc.
Day Eight – Bilaminar Disc • a small cavity appears within the epiblast. • This cavity enlarges to become the amniotic cavity. Soon amniogenic (amnion-forming) cells-amnioblasts-separate from the epiblast and form the amnion, which encloses the amniotic cavity
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Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast
Day Nine • defect in the surface epithelium is closed by a fibrin coagulum. • vacuoles appear in the syncytium. When these vacuoles fuse, they form large lacunae, and this phase of trophoblast development is thus known as the lacunar stage.
Primitive yolk sac Day Nine flattened cells probably originating from the hypoblast form a thin membrane, the exocoelomic (Heuser’s) membrane
Exocoelomic cavity: formed when cells from the hypoblast line the cytotrophoblast Will soon become the primary yolk sac and then the secondary yolk sac Day Nine
Day Nine Extraembryonic coelom / chorionic cavity: formed by large cavities in the extraembryonic mesoderm
Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Primary Yolk Sac Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast
Day Eleven & Twelve • the blastocyst is completely embedded in the endometrial stroma, and • the surface epithelium covers the original defect • The trophoblast is characterized by lacunar spaces in the syncytium
Day Eleven & Twelve • sinusoids • The syncytial lacunae become continuous with the sinusoids, and maternal blood enters the lacunar system. • As the trophoblast continues to erode more and more sinusoids, maternal blood begins to flow through the trophoblastic system, establishing the primordial uteroplacental circulation.
Day Eleven & Twelve • a new population of cells(derived from yolk sac cells) appears between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity. • Primitive yolk sac
Day Eleven & Twelve • Development of extraembryonic coelom, • Except where the germ disc is connected to the trophoblast by the connecting stalk .
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Day Thirteen – More stuff happens -the hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane. -These cells proliferate and gradually form a new cavity within the exocoelomic cavity. - -This new cavity is known as the secondary yolk sac or definitive yolk sac. -This yolk sac is much smaller than the original exocoelomic cavity, or primitive yolk sac. --During its formation, large portions of the exocoelomic cavity are pinched off. These portions are represented by exocoelomic cysts, which are often found in the extraembryonic coelom or chorionic cavity. Extraembryonic coelom expands and forms the chorionic cavity Connecting stalk: where extraembryonic mesoderm traverses through the chorionic cavity. Develops into the umbilical cord.
aka chorionic cavity
Day Thirteen – More stuff happens • the extraembryonic coelom expands and forms a large cavity, the chorionic cavity. • The extraembryonic mesoderm lining the inside of the cytotrophoblast is then known as the chorionic plate.
Day Thirteen and Fourteen • primary chorionic villi. • The prechordal plate develops as a localized thickening of the hypoblast,
Sadler, Langman´s Medical Embryology, 2004 Microphotography: Heuser CH, Rock J, Hertig AT: Contrib Embryol Carnegie Instn, Wash 31:85, 1945 13-day implanted human blastocyst Extraembryonic mesoderm somatic (somatopleuric): attached to the trophoblast – chorionic plate (3) attached to the amnioblasts (4)- amnion splanchnic (splanchnopleuric) attached to the endoderm of the yolk sac (6) exocoelomic cyst (2) Primary chorionic villi Maternal sinusoid Prechordal plate Trophoblast lacunae Extraembryonic coelom (1) Chorionic cavity Trophoblast lacunae 2 1 Amnionic cavity (AC) AC Secondary yolk sac (sYS) sYS Connecting stalk 3 4 6
So far – three cavities Amniotic Cavity • Will eventually surround the embryo after folding Secondary Yolk Sac • Formerly primary yolk sac, which was formerly the exocoelomic cavity Chorionic Cavity • Formerly EXTRAembryonic coelom
Chorionic cavity eventually goes!
Ectopic Pregnancy Implantation of blastocysts usually occurs in the endometrium of the uterus, superior in the body of the uterus, slightly more often on the posterior than on the anterior wall.
Definition Failure of implantation of a fertilized ovum inside the endometrial cavity. OR Development of the pregnancy outside its normal place for implantation. 300
Cause 1) Previous Tubal Infections 2) Previous Tubal or Pelvic Surgery 3) Hormonal Factors- interfere with normal tubal motility of the fertilized ovum 4) Contraceptive Failure- interfere with normal tubal motility of the fertilized ovum 5) Stimulation of Ovulation- stimulating drugs for ovulation- These drugs alter the estrogen/progesterone level, which can affect tubal motility 6) Infertility Treatment (with in vitro fertilization (IVF) or gamete intrafallopian transfer (GIFT) since underlying tubal damage is frequently one of the causative factors predisposing one to this type of infertility treatment.) 7) Environmental Effect- Maternal cigarette smoking at the time of conception was found in a case-controlled study, to be associated with an increased risk of an ectopic pregnancy 8) Transmigration of Ovum Migration of the ovum from one ovary to the opposite fallopian tube can occur by an extrauterine or intrauterine route. This can cause a potential delay in transportation of the fertilized ovum to the uterus. Then trophoblastic tissue is present on the blastocyst before it reaches the uterine cavity, and therefore the trophoblastic tissue implants itself on the wall of the fallopian tube. 301
Sites of ectopic pregnancy Tubal pregnancy Most common type of ectopic pregnancy with most common location being the ampulla Ampullary 80% Isthmic 12% Fimbrial end 5% Cornoal and interstitial 2% 1/10/2024 302 SFB
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Sites of ectopic pregnancy Abdominal Pregnancy (1.4%) Implantation occurs in the peritoneal cavity Primary Directly in the abdominal cavity Secondary Secondary to tubal rupture and abortion Ovarian pregnancy(.2%) One that develops in the ovary (criteria for diagnosis: gestational sac occupies normal location of the ovary, sac connected to the uterus by uteroovarian ligament, ipsilateral tube intact, ovarian tissue in the wall of the 304
Cervical pregnancy(.2%) In the cervical canal below the internal os 305 In very rare cases the fertilized ovum bypasses the uterine endometrium and implants itself in the cervical mucus.
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Quick Summary • Fertilised egg cleaves and implants • Bilaminar disc forms (epiblast and hypoblast) • Cavities start forming (amniotic, yolk sac, chorionic)
Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Yolk Sac Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast Ectoderm Mesoderm Endoderm GASTRULATION
The second week of development is known as the week of twos: the trophoblast – (the cytotrophoblast and syncytiotrophoblast.) The embryoblast- ( the epiblast and hypoblast). The extraembryonic mesoderm – ( the somatopleure and splanchnopleure). Two cavities-the amniotic and yolk sac cavities, form.
Week Three Trilaminar Germ Disc
Gastrulation The process that establishes all three germ layers in the embryo.
What contribute to gastrulation? 315
Extensive cell shape changes, Rearrangement, Movement, and Changes in adhesive properties contribute to the process of gastrulation.
Epiboly Convergent extension movement of sheets of cells which tend to cover other cells
 Rapid development of the embryo from the embryonic disc during the third week is characterized by  Appearance of primitive streak (the first sign of gastrulation)  Development of notochord  Differentiation of three germ layers
Primitive streak 324
325 Thickened linear band the primitive stre
As soon as the primitive streak appears, it is possible to identify the embryo's craniocaudal axis, its cranial and caudal ends, its dorsal and ventral surfaces, and its right and left sides. The primitive groove and pit result from the invagination (inward movement) of epiblastic cells-Mesenchymal
Shortly after the primitive streak appears, cells leave its deep surface and form mesenchyme, Mesenchyme is a tissue consisting of loosely arranged cells suspended in a gelatinous matrix. Mesenchymal cells are ameboid and actively phagocytic . Mesenchyme forms the supporting tissues of the embryo, such as most of the connective tissues of the body and the connective tissue framework of glands. Some mesenchyme forms mesoblast (undifferentiated mesoderm), which forms the intraembryonic, or embryonic, mesoderm . Cells from the epiblast ,the primitive node and other parts of the primitive streak displace the hypoblast, forming the embryonic endoderm in the roof of the umbilical vesicle. The cells remaining in the epiblast form the embryonic ectoderm.
• Mesenchymal cells (pluripotential cells) derived from the primitive streak migrate widely and proliferate and differentiate into diverse types of cells, such as fibroblasts, chondroblasts, and osteoblasts . • In summary, cells of the epiblast, through the process of gastrulation, give rise to all three germ layers in the embryo, the primordia of all its tissues and organs.
Fate of the Primitive Streak • The primitive streak actively forms mesoderm by the ingression of cells until the early part of the fourth week; thereafter, production of mesoderm slows down. • The primitive streak diminishes in relative size and becomes an insignificant structure in the sacrococcygeal region of the embryo. • Normally the primitive streak undergoes degenerative changes and disappears by the end of the fourth week.
Female infant with a large sacrococcygeal teratoma that developed from remnants of the primitive streak Persistence of primitive streak that proliferates and forms new growth at the sacrococcyg eal area
Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Yolk Sac Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast Ectoderm Mesoderm Endoderm
NOTOCHORDAL PROCESS AND NOTOCHORD 342
median cellular cord, the notochordal process
NOTOCHORDAL PROCESS AND NOTOCHORD • Prechordal mesoderm(b/n PP &NP) - essential in forebrain and eye induction. • The prechordal plate have a role as a signaling center for controlling development of cranial structures.
Function of The notochord 1. Defines the primordial longitudinal axis of the embryo and gives it some rigidity 2. Provides signals that are necessary for the development of axial musculoskeletal structures and the central nervous system 3. Contributes to the intervertebral discs 4. Degenerates as the bodies of the vertebrae form, but small portions of it persist as the nucleus pulposus of each intervertebral disc. 5. The developing notochord induces the overlying embryonic ectoderm to thicken and form the neural plate, the primordium of the central nervous system (CNS).
Migration of mesenchym and mesodermal cell From primitive streak and notochordal process 352
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Migration of mesenchym and mesodermal cell 1. laterally and cranially-- margins of the embryonic disc. --Continuous EE mesoderm
Cranially On each side of the notochordal process and around the prechordal plate 358
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Migration of mesenchym and mesodermal cell • By the middle of the third week, intraembryonic mesoderm separates the ectoderm and endoderm everywhere except  At the oropharyngeal membrane cranially  In the median plane cranial to the primitive node, where the notochordal process is located  At the cloacal membrane caudally
THE ALLANTOIS 362
THE ALLANTOIS • The allantois appears on ~ day 16 as a small, sausage-shaped diverticulum (outpouching) from the caudal wall of the umbilical vesicle that extends into the connecting stalk
Allantois -It appears on day 16 from caudal end of yolk sac into connecting stalk. -It is involved with early blood formation and associated with urinary bladder development. -It becomes urachus and remains as median umbilical ligament Yolk sac Connecting stalk  umbilical cored
NEURULATION FORMATION OF THE NEURAL TUBE 368
- The processes involved in the formation of the neural plate, neural folds and closure of the folds to form the neural. - It is completed by the end of the 4th week ,when closure of the caudal neuropore occurs. - The embryo is called neurula during neurulation.
Neural Plate and Neural Tube 370
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Gastrulation to neurulation Neural plate Precordal plate Neural plate Notochordal plate
Neural Crest Formation 385
Formation of Neural Crest Cells Neural tube Notochord Melanocytes Schwann cells; Meninges (pia, arach) Cells of suprarenal medulla Autonomic ganglion cells Surface ectoderm Cranial sensory ganglion cells Posterior root ganglion cells Neural crest 388 forms sensory ganglia of spinal (dorsal root ganglia), cranial nerves (V, VII, IX, X) and ganglia of the autonomic nervous system V, VII, IX, X
Secondary neurulation - Neuropores close: -Cranial neuropore (day 24)  forebrain -Caudal neuropore (day 26)  somite 31(S2) -Mesodermal caudal eminence  neural cord  neural tube Neural tube (CNS) and neural crest (PNS) derived from ectoderm Caudal neural tube derived form mesoderm
Failure of neurulation:
DEVELOPMENT OF SOMITES 400
401
402
The paraxial mesoderm
Paraxial mesoderm is organized, cephalocaudally, into segments known as: – Somitomeres: more loosely organized in the head region forming in association with segmentation of the neural tube into neuromeres – Somites: more compact and defined regions forming from the occipital region caudally; first somite forms on the 20th day, and last pair at the end of the 5th week
Somite period of human development
About 38 pairs of somites form during the somite period of human development (days 20 to 30). By the end of the fifth week, 42 to 44 pairs of somites are present
E21 days E22 days E24 days
By the end of the fifth week, 42 to 44 pairs of somites are present
Somites ( 44 Pairs) They are- 4 Occipital 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral Coccygeal 8-10 • Later 1st Occipital and last 5 -7 Coccygeal disappear
Fate of the Somites Each somite can be divided into two main portions: sclerotome and dermomyotome; it also receives its own segmental nerve component The sclerotome is the ventromedial portion of the somite which forms a loosely organized tissue (the mesenchyme) and migrates around the notochord and spinal cord, forming the vertebral column, in addition to forming tendons for its muscles
Intermediate Cell Mass Mesoderm Intermediate mesoderm (nephrogenic cord) differentiates into urogenital Structures (kidney, testis & ovary)
Lateral Plate Mesoderm:  spaces appear in it & fuse forming a U- shaped cavity (intraembryonic coelom), formed of 3 parts:  2 longitudinal pleuro- peritoneal canals: gives 2 pleural & 2 peritoneal cavities.  A transverse cranial part: gives pericardial sac.
Lateral Plate Mesoderm The lateral plate mesoderm is divided into: Parietal (somatic) layer facing the ectoderm. Together they form the intraembryonic somatopleure. it gives the muscles and connective tissue of the ventral & lateral body wall Visceral (splanchnic) layer facing endoderm. Together they form the intraembryonic splanchnopleure. It gives the smooth muscles of the viscera (gut).
The Cranial Part Of Intra- embryonic Mesoderm • The cardiogenic plate: • Cranial to the oral membrane a condensation of intra- embryonic mesoderm is present & called the cardiogenic plate which will give rise to the heart. • The septum transversum: • Cranial to the cardiogenic plate, there is another mass of intra-embryonic mesoderm is called septum transversum which forms the future diaphragm.
DEVELOPMENT OF THE INTRAEMBRYONIC COELOM -Intraembryonic coelom (cavity) --fusion of isolated coelomic spaces in the lateral mesoderm and cardiogenic mesoderm into a horseshoe-shaped cavity. -Lateral mesoderm divided into: -A somatic or Parietal layer--together with extraembryonic mesoderm covering amnion and ectoderm called somatopleure, embryonic body wall (upper side) -A splanchnic or Visceral layer--together with extraembryonic mesoderm covering yolk sac and endoderm is called splanchnopleure, embryonic gut wall (lower side) -During the 2nd month, intraembryonic coelom is divided into 3 body cavities: 1. pericardial cavity 2. pleural cavities 3. peritoneal cavity
Dr: Azza ZAki Differentiation Of The Endoderm
Differentiation Of The Endoderm • 1-The Gut: • The endoderm initially is a flat layer of cells covering the surface of the embryonic disc that faces the yolk sac. • With the formation of the head & tail folds, parts of the yolk sac become enclosed within the embryo. A tube lined by endoderm is formed (primitive gut) from which most of gastrointestinal tract is formed.
The part of the gut cranial to communication with the yolk sac is called the foregut& the part caudal to this communication is called the hindgut while the intervening part is called the midgut. The midgut is associated with the yolk sac via the vitelline duct.
Communication Of The Gut: The mouth begins as a depression on the surface ectoderm called stomodeum. This is separated from the foregut by the buccopharyngeal membrane which ruptures. The proctodeum is a depression of the surface ectoderm at the tail end of the embryo. This is separated from the hindgut by the cloacal membrane which ruptures.
Derivatives Of The Endoderm  Epithelial lining of the alimentary tract.  Epithelium of the glands develop from the alimentary tract; the thyroid, parathyroid, liver& pancreas. • The epithelium lining of the respiratory tract (trachea, bronchi &lung).
Derivatives Of The Endoderm • Epithelial lining of the urinary bladder. • Epithelial lining of the pharyngeotympanic tube ,tympanic cavity and mastoid antrum • Tonsil.
EARLY DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM
WHY early cardiovascular system ? • The urgent need for blood vessels to bring oxygen and nourishment to the embryo from the maternal circulation through the placenta. • During the third week, a primordial uteroplacental circulation develops
EARLY DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM Embryonic Nutrition 2nd week -maternal blood by diffusion through the extraembryonic coelom and umbilical vesicle. 3rd week, vasculogenesis and angiogenesis (Gr. angeion, vessel + genesis, production), or blood vessel formation, begins in the extraembryonic mesoderm of the umbilical vesicle, connecting stalk, and chorion.
Vasculogenesis and Angiogenesis The formation of the embryonic vascular system involves two processes: 1. Vasculogenesis is the formation of new vascular channels by assembly of individual cell precursors called angioblasts. 2. Angiogenesis is the formation of new vessels by budding and branching from preexisting vessels.
Blood vessel formation (vasculogenesis) in the embryo and extraembryonic membranes during the third week may be summarized as follows
• The first blood islands appear in mesoderm surrounding the wall of the yolk sac at 3 weeks of development and slightly later in lateral plate mesoderm and other regions
• These islands arise from mesoderm cells that are induced to form hemangioblasts, a common precursor for vessel and blood cell formation. • Hemangioblasts in the center of blood islands form hematopoietic stem cells, the precursors of all blood cells, whereas peripheral hemangioblasts differentiate into angioblasts, the precursors to blood vessels. These angioblasts proliferate and are eventually induced to form endothelial cells .
441
Blood and Blood vessels • Hemangioblasts- are derived from mesenchymal cells • Central cells become primitive blood cells and peripheral cells form endothelial cells of blood vessels
443 Hemangioblast s
Angioblasts of Hemangioblasts 444
• Mesenchymal cells (mesoderm derived) differentiate into endothelial cell precursors- angioblasts (vessel-forming cells), which aggregate to form isolated angiogenic cell clusters called blood islands, • Small cavities appear within the blood islands and endothelial cords by confluence of intercellular clefts.
• Angioblasts flatten to form endothelial cells that arrange themselves around the cavities in the blood island to form the endothelium. • These endothelium-lined cavities soon fuse to form networks of endothelial channels (vasculogenesis). • Vessels sprout into adjacent areas by endothelial budding and fuse with other vessels.
Angiogenesis • Once the process of vasculogenesis establishes a primary vascular bed, which includes the dorsal aorta and cardinal veins, additional vasculature is added by angiogenesis, the sprouting of new vessels
Angiogenesis
Embryonic vessels first form mainly in the aorta-gonad-mesonephros area; then in the liver; then the definitive hematopoietic area, the bone marrow
The Primitive Circulation The heart begins beating at the beginning of the forth week; the cardiovascular system is the first functional system to develop
Hematopoietic stem cells of Hemangioblasts Central cells 452
• Cavities appear within the blood island; central cells become hematopoietic stem cells (the ancestor of all types of blood cells) 453
Blood cell formation Transitory Definitive blood cells
Transitory As mentioned, the first blood cells arise in the blood islands of the yolk sac, but this population is transitory. 455
Definitive blood cells 456
• The definitive hematopoietic stem cells arise from mesoderm surrounding the aorta in a site called the aorta-gonad-mesonephros region (AGM). • These cells will colonize the liver, which becomes the major hematopoietic organ of the fetus. Later, stem cells from the liver will colonize the bone marrow, the definitive blood-forming tissue. 457
Fused dorsal aortae from 4th thoracic somite to 4th lumbar somite Dorsal aortae 1st aortic arch Aortic sac Heart tube
The mesenchymal cells surrounding the primordial endothelial blood vessels differentiate into the muscular and connective tissue elements of the vessels.
The Primordial Cardiovascular System the heart -The heart and great vessels form from mesenchymal cells in the cardiogenic area.
Early development of Heart and BV Angioblastic cords Heart tubes Endocardial tubes
Primordial cardiovascular system -The tubular heart joins with blood vessels in the embryo, connecting stalk, chorion, and umbilical vesicle to form a 464
• The cardiovascular system is the first organ system to reach a functional state.
• The embryonic heartbeat can be detected using Doppler ultrasonography during the fifth week, approximately 7 weeks after the last normal menstrual period.
DEVELOPMENT OF CHORIONIC VILLI • Shortly after primary chorionic villi appear at the end of the second week, they begin to branch. • Early in the third week, mesenchyme grows into these primary villi, forming a core of mesenchymal tissue. The villi at this stage-secondary chorionic villi-cover the entire surface of the chorionic sac
Sadler, Langman´s Medical Embryology, 2004 Microphotography: Heuser CH, Rock J, Hertig AT: Contrib Embryol Carnegie Instn, Wash 31:85, 1945 13-day implanted human blastocyst Extraembryonic mesoderm somatic (somatopleuric): attached to the trophoblast – chorionic plate (3) attached to the amnioblasts (4)- amnion splanchnic (splanchnopleuric) attached to the endoderm of the yolk sac (6) exocoelomic cyst (2) Primary chorionic villi Maternal sinusoid Prechordal plate Trophoblast lacunae Extraembryonic coelom (1) Chorionic cavity Trophoblast lacunae 2 1 Amnionic cavity (AC) AC Secondary yolk sac (sYS) sYS Connecting stalk 3 4 6
• Some mesenchymal cells in the villi soon differentiate into capillaries and blood cells. • They are called tertiary chorionic villi when blood vessels are visible in them. The capillaries in the chorionic villi fuse to form arteriocapillary networks, which soon become connected with the embryonic heart through vessels that differentiate in the mesenchyme of the chorion and connecting stalk.
• Capillaries in tertiary villi make contact with capillaries developing in mesoderm of the chorionic plate and in the connecting stalk . • These vessels, in turn, establish contact with the intraembryonic circulatory system, connecting the placenta and the embryo. • Hence, when the heart begins to beat in the fourth week of development, the villous system is ready to supply the embryo proper with essential nutrients and oxygen.
• By the end of the third week, embryonic blood begins to flow slowly through the capillaries in the chorionic villi. • Oxygen and nutrients in the maternal blood in the intervillous space diffuse through the walls of the villi and enter the embryo's blood. Carbon dioxide and waste products diffuse from blood in the fetal capillaries through the wall of the chorionic villi into the maternal blood.
cytotrophoblastic cells cytotrophoblastic shell, which gradually surrounds the chorionic sac and attaches it to the endometrium. Villi that attach to the maternal tissues through the cytotrophoblastic shell are stem chorionic villi (anchoring villi). Those that branch from the sides of stem villi are free (terminal) villi, through which exchange of nutrients and other factors will occur
• The villi that grow from the sides of the stem villi are branch chorionic villi (terminal villi). It is through the walls of the branch villi that the main exchange of material between the blood of the mother and the embryo takes place. The branch villi are bathed in continually changing maternal blood in the intervillous space.
ambo embryology 1yr.ppt- health education
ambo embryology 1yr.ppt- health education
ambo embryology 1yr.ppt- health education

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ambo embryology 1yr.ppt- health education

  • 1. Overview of Anatomy Anatomy – the study of the structure of body parts and their relationships to one another
  • 2.
  • 3. Sub division of anatomy
  • 4. 1. Gross or macroscopic Study large body structures visible to the necked eye
  • 5. 2. Microscopic Study examination of body tissue using a microscope
  • 6. 2. Microscopic A. Cytology – study of the cell B. Histology – study of tissues
  • 8. Embryology – study of developmental changes of the body before birth
  • 9. 9 He who sees things grow from the beginning will have the finest view of them. Aristotle, 384-322 BC
  • 10. Developmental Periods Divide Prenatal (before birth) and Postnatal (after birth) periods 10
  • 12. Embryology  Embryology : – is the science which deals with the prenatal stage i.e. the intrauterine development of the human body till birth. 12
  • 13. Teratology • (Gr. teratos, monster) • Is the division of embryology and pathology that deals with abnormal development (birth defects). • This branch of embryology is concerned with various genetic and/or environmental factors that disturb normal development and produce birth defects 13
  • 14. Embryology 1.Prenatal period : a) Germinal period  Is the period from fertilization till formation of germ disk.  Its duration is about (18-21) days .  Safe period (non – sensitive to teratogenic agents ). 14
  • 15. Embryology 1.Prenatal period : b) Embryonic period • is the period formation of germ disk till organogenesis . • its duration is from 4th week to 8th week . • Risk period (sensitive to teratogenic agents ). 15
  • 16. Embryology 1. Prenatal period : C) Fetal period • is the period from organogenesis till birth. • during this period there are :- – Rapid body and organ growth . – The brain , ear , eyes , teeth , adrenal glands , the external genitalia continue development in this period . – There is a relative reduction of head growth compared to body growth . • less-safe period (less sensitive to teratogenic agents ) 16
  • 17. Developmental period 2. Postnatal period (new born / off spring /neonate ): The changes occurring in the body after birth . 3. Gerology: The changes of body of old ages : 17
  • 19. • A human being is formed of trillions of cells; these cells are of two types: A. Somatic cells- which are present in the whole tissues of the body B. Gametes which are the sperms and ova 19
  • 20. A. Somatic cell • Each Som. C nucleus contain 46 chromosomes which are as follow • 22 pair of identical chromosome- autosomes • One pair of sex chromosomes which differ in the two sexes • 23,x 20
  • 21. • The two chromosomes in each pair are called homologous chromosome • One is inherited from the mother and the other is from the father • Somatic cells are described as Diploid because their chromosomes are in homologus pair 21
  • 22. Female somatic cell • The pair of sex chromosomes are identical and are called XX chromosomes. 22
  • 23. Male somatic cells • The pair of sex chromosomes are quit different • One being long and is known as X chromosome • The other is much smaller and is known as Y 23
  • 24. Homologous Chromosomes • Pair of chromosomes (maternal and paternal) that are similar in shape and size. • Homologous pairs (tetrads) carry genes controlling the same inherited traits. • Each locus (position of a gene) is in the same position on homologues. • Humans have 23 pairs of homologous chromosomes. 22 pairs of autosomes 1 pair of sex chromosomes
  • 25. Homologous Chromosomes (because a homologous pair consists of 4 chromatids it is called a “Tetrad”) Paternal Maternal eye color locus eye color locus hair color locus hair color locus
  • 26. Humans have 23 Sets of Homologous Chromosomes Each Homologous set is made up of 2 Homologues. Homologue Homologue
  • 27. Autosomes (The Autosomes code for most of the offspring’s traits) In Humans the “Autosomes ” are sets 1 - 22
  • 28. Sex Chromosomes The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male. XX chromosome - female XY chromosome - male In Humans the “Sex Chromosomes” are the 23rd set
  • 29. Gamete (ovum or sperm) • Germ cell beyond a certain stage of development are haploid. • At fertilization one set of paternal (sperm) chromosomes unites with one set of maternal(egg) chromosomes, restoring the somatic cells that arise from it 29
  • 30. • Although the two chromosomes of a homologous pair appear to be identical, they come from different parents and therefore are not genetically identical. 30
  • 31. Sex Chromosomes The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male. XX chromosome - female XY chromosome - male In Humans the “Sex Chromosomes” are the 23rd set
  • 32. Sex Chromosomes “Sex Chromosomes” …….the 23rd set 23 This person has 2 “X” chromosomes… and is a female.
  • 33. 33 Cell Type No. of chromosomes, Amount of DNA n Primordial germ cells n Spermatogonia n Oogonia n Zygote n Blastomeres n All normal somatic cells 46, 2n n Primary spermatocytes n Primary oocytes 46, 4n n Secondary spermatocytes n Secondary oocytes 23, 2n n Spermatid, spermatozoa n Mature oocytes (Ova) 23, n
  • 34. Organization of the chromatin A human cell usually has 46 molecules of DNA with an average length of 44mm(total slightly over 2m) 34
  • 35. • To put this in perspective, if a DNA molecule were the thickness of a telephone pole, it would reach about 4,400km into space-far higher than the orbits of satellites and spece shuttles. 35
  • 36. • Imagine trying to make a pole 20cm thick and 4,400km long without breaking it!. The problem for a cell is even greater. 36
  • 37. 37
  • 38. 38
  • 39. 3 Types of Cell Division • Amitosi- direct cell division-lower animal • Mitosis – ordinary somatic cell division – 2 daughter cells with identical chromosomes and genes to parents – Diploid cells – 2n chromosome complement • Meiosis – germline cell division – Results in formation of gametes – cells with only 23 chromosomes – Haploid cells – n chromosome complement 39
  • 40. Mitosis • The somatic cells start their life as daughter cells after mitotic cell division. They then perform their specific functions till they divided again • An indirect cell division involving four phases prophase Metaphase Anaphase and Telophase followed by Interphase 40
  • 41. INTERPHASE • The cell prepare itself for mitosis. • Nuclear membrane and nucleolus are very distinct. • Chromosomes appear like threads or filaments (chromatids). • Divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap) 41
  • 42. Phases of Interphase • G1 (gap 1) – cell grows by producing proteins and cytoplasmic organelles • S (synthesis) – replication of the chromosomes • G2 (gap 2) – cell continue to grow and further protein synthesis occur 42
  • 43. Cell Cycle of a Somatic Cell 1. Interphase 1. G1 2. S 3. G2 G1 + S + G2 phases = 16-24 h 2. Mitosis 43
  • 44. The Cell Cycle G1 – Gap 1 (Lasts hours, days or years) – cell grows by producing proteins and cytoplasmic organelles – Occurs after mitosis and before S phase 44 end cells
  • 45. The Cell Cycle • G0 phase Some cells may leave G1 stage permanently to perform their specialized functions, these cells are then called end cells – Resting stage/quiescent stage – Neurons, RBCs arrested in G1 = G0 phase – permanent G1 phase – Liver cells enter G0 but on damage  G1 and cell cycle continues 45
  • 46. The Cell Cycle S phase – Stage of DNA synthesis – Each chromosome replicates  bipartite chromosome made up of sister chromatids – End of each chromatid marked by telomeres – specialized DNA sequences that ensure integrity of chromosomes during division – Sister chromatids held together at centromere – region of DNA associated with kinetochore – Provide a binding site for microtubules – DNA replication happens at thousands of origins of DNA replication – replication of the chromosomes 46
  • 47. The Cell Cycle G2 phase – Gap 2 – A very short period – The cell is preparing for mitosis – Cell’s DNA doubled in S phase – Brief stage – cell continue to grow and further protein synthesis occur 47
  • 48. Figure 17-31 Molecular Biology of the Cell (© Garland Science 2008) Centriole Replication • At a certain point in G1, the two centrioles of the pair separate. • During S phase, a daughter centriole begins to grow near the base of each mother centriole and at a right angle to it. • The elongation of the daughter centriole is usually completed by G2 48 centrosome
  • 49. Mitosis • Mitosis: shortest of 4 stages • Important component: chromosomal segregation – process of distributing copy of each chromosome to each daughter cell • 5 stages: 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase 49
  • 50. Mitosis is subdivided into prophase, prometaphase, metaphase, anaphase, and telophase • Prophase: Condensed chromosome start to become visible, Centrosomes start moving apart, Nucleolus starts disappearing • Prometaphase: Nuclear membrane breaks down • Metaphase: Chromosomes maximally condensed and align at the metaphase plate • Anaphase: The two sister chromatids separate and move toward opposite poles • Telophase: nucleus reassembly occurs, cytokinesis occurs 50
  • 51. 51
  • 52. Prophase • Condensation of chromosomes • Disintegration and disappearance of nucleolus • Formation of mitotic spindle – microtubule network 52 Prometaphase n Nuclear membrane breaks up n Congression occurs – chromosomes move to point midway between spindle poles n Condensation of chromosomes continue
  • 53. Metaphase • Maximum condensation of chromosomes reached • Arranged at equatorial plane of cell • Balanced forces of microtubules from opposite poles at kinetochores 53
  • 54. Anaphase • Begins when sister chromatids separate • Sister chromatids separate into daughter chromosomes • Daughter chromosomes move to opposite poles 54
  • 55. Telophase and Cytokinesis • Telophase – Chromosomes decondense – Nuclear membrane reforms • Cytokinesis divides the cytoplasm – Cleavage begins as a slight indentation in cell surface deepens into a cleavage furrow. – Actin contractile ring and myosin motors drive the process – Cytoplasm cleaves separating daughter cells • Larger organelles, such as ER and Golgi, tend to fragment into small vesicles early in mitosis and then reassemble in daughter cells 55
  • 56. Function of mitosis • Formation of a multicellular embryo from a fertilized egg • Tissue growth • Replacement of old and dead cells and • Repair of injured tissue • Egg and sperm are produced by a combination of mitosis and meiosis 56
  • 57. 57
  • 58. 58
  • 59. 59
  • 60. What if for gametogenesis • Sexual reproduction- bi-parental • If make a child-combined gamet • There must be a mechanism Keep chromosome number constant from generation to generation • 46 sperm chromosome 46 egg chro= 92+92=184 and forth 60
  • 61. What if for gametogenesis • To prevent the chromosome number from doubling in every generation, the number is reduced by half during gametogenesis. 61
  • 62. Meiosis • One round of DNA synthesis  2 rounds of chromosomal segregation – Meiosis I – reduction division – chromosome no. goes from diploid  haploid • Meiotic crossing over or recombination also occurs here: homologous segments of DNA exchanged between nonsister chromatids of pair of homologous chromosomes • Recombination important also for chromosome segregation – Meiosis II – like mitosis without a preceding DNA replication stage • Sister chromatids separate 62
  • 63. Meiosis • Meiosis can convert one diploid cell into four haploid cells – Meiosis I: the first meiotic division – Homologous pairs join together to form a bivalent • Meiosis I produces two haploid cells that have chromosomes composed of sister chromatids – Unlike mitosis, in meiosis I, sister chromatids stay together. – Thus, the cells at the end of meiosis I are considered haploid because it contains only one of the two chromosomes of each bivalent – Genetic recombination 63
  • 64. Meiosis I • Prophase I: Homologous chromosomes become paired and exchange DNA – Divided into 5 stages – Formation of synaptonemal complex and crossing-over occurs • Metaphase I: Bivalents align at the spindle equator – The kinetochores of sister chromatids lie side by side and face the same pole of the cell – Random orientation of maternal or paternal chromosomes – Chromosomes held together by chiasmata • Anaphase I: Homologous chromosomes move to opposite spindle poles • Telophase I and cytokinesis: Two haploid cells are produced 64
  • 65. 65
  • 66. Prophase I • Leptotene – chromatin begin to condense, 2 sister chromatids so close, cannot be distinguished • Zygotene – Homologs pair along entire length – synapsis – Chromosomes held together by synaptonemal complex • Pachytene – Synapsis complete, chromosome more tightly coiled – Chromosome appear bivalent – tetrad formation – Recombination takes place • Diplotene – Synaptonemal complex disappears – Bivalents begin to separate but held together at centromeres a– chiasmata • Diakinesis – stage of max condensation 66
  • 67. 67
  • 68. • The lateral elements of the synaptonemal complex start to attach to individual chromosomes during leptotene • The central element, which actually joins homologous chromosomes, does not form until zygotene • The formation of the synaptonemal complex is essential for recombination and for preventing aneuploidy 68
  • 70. Anaphase I • Disjunction occurs – members of each bivalent move apart – HOMOLOGS (and usually alleles) SEPARATE!!! • Maternal and paternal chromosomes sort independently  223 combinations 70 Metaphase I n Nuclear membrane disappears n Spindle forms n Bivalents align at equator
  • 71. Telophase I & Cytokinesis • Telophase I – 2 chromosome sets groups at opposite poles • Cytokinesis – cell divides into daughter cells  enter meiotic interphase (no DNA synthesis) – Spermatogenesis: equal – Oogenesis: secondary oocyte receives most cytoplasm, other cell  1st polar body 71
  • 72. Meiosis II • Meiosis II resemble a mitotic division • Prophase II is very brief • Metaphase II – Kinetochores of sister chromatids now face in opposite directions • Anaphase II – Sister chromatids separate 72
  • 73. Genetic Consequences of Meiosis • At the end of meiosis II there are four daughter cells, each containing a haploid set of chromosome – Reduction of chromosome number • Segregation of alleles • Random assortment of the homologues (law of independent assortment) – Meiosis generates genetic diversity – Over 8 million different combinations of chromosomes • Addition shuffling by crossing over • Nondisjunction refers to the failure of the two members of a homologous chromosome pair to separate during anaphase – Leads to aneuploidy diseases (trisomy 21-Down syndrome) 73
  • 74. Comparison of Mitosis with Meiosis 74
  • 75. 75 Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 2 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction
  • 76. Sexual reproduction • To reproduce sexually means that the parents must produce gametes(sex cell) that can meet and combine their genes in a Zygote(fertilized egg) 76
  • 77. Embryology Gametogenesis (Formation of gametes ) Spermatogenesis=Formation of sperms (Male reproductive system) testis Oogenesis=Formation of Ova (Female reproductive system) ovary 77
  • 78. Male genital system 1. The testis : Is the male sex gland . it lies in the scrotum suspended by the spermatic cord .it is enclosed by an isolated part of the coelomic membrane (the tunica vaginalis). The testis is divided into 250 compartments (lobes). Each containing (1-3)seminiferous tubules . The interstitial cells :produce the male sex hormone (testosterone). 78
  • 79. Male genital system Male reproductive system 79
  • 80. 80
  • 81. Male genital system 2. Seminiferous tubules: (For formation of sperms) Seminiferous tubules contain 2 types of cells : • PGC----Spermatogonia (stem cells) – for production of sperms through process of spermatogenesis . • Sertoli cells (supporting cells): – Give nourishment to developing spermatids. – Give supporting to spermatogonia and spermatids. – Eat the excess parts of spermatids during spermiogenesis. 81
  • 82. 82
  • 83. 83
  • 84. Male genital system 3. Epididymis : – storage and maturation of sperms . – Adding two layers around the sperm (glycoprotein coat and seminal protein coat.) 84
  • 85. Male genital system 4. The accessory glands : – Seminal vesicle : Secretes 60% of seminal fluid which contain fructose sugar (for nutrition). – Prostate gland :Secretes 20% of seminal fluid which contain bicarbonate for alkalization of acidic urine and give milky appearance of semen . – Cowper’s gland (bulbo-urethral gland) :Secretes 20% of seminal fluid which increase viscosity of the semen 85
  • 86. Male genital system  Notes: Primordial germ cells (PGC): They are originated from the wall of the yolk sac at the end of 3rd week of embryonic development. These cells migrate by amoeboid movement from the yolk sac toward the developing gonads (primitive sex glands), where they arrive at the end of 4th week and invading the genital ridges in 6th week of development. PGC influence of development of the gonads into testes or ovaries . 86
  • 87. Primordial germ cells Yolk sac The first human germ cells (primordial germ cells) appear in the wall of the yolk sac (3rd week) 87
  • 88. The germ cells, through amoeboid movement, move towards the gonads where they arrive at about 5th week Primordial cells later differentiate into mature gametes i.e. spermatogonia (male) or oogonia (female) Primordial germ cells Yolk sac 88
  • 89. 89
  • 90. Spermatogenesis • Spermatogonia, which have been dormant in the seminiferous tubules of the testes since the fetal period, begin to increase in number at puberty. • After several mitotic divisions, the spermatogonia grow and undergo changes producing successive generations of cells . 90
  • 91. Spermatogenesis • The newly formed cells can follow one of two paths: they can continue dividing as stem cells, also called type A spermatogonia, or they can differentiate during progressive mitotic cycles to become type B spermatogonia. 91
  • 92. Spermatogenesis • Type B spermatogonia are progenitor cells that will differentiate into primary spermatocytes . • The primary spermatocyte has 46 (44 + XY) chromosomes and 4N of DNA. (N denotes either the haploid set of chromosomes [23 chromosomes in humans] or the amount of DNA in this set.) 92
  • 93. Spermatogenesis • Soon after their formation, these cells enter the prophase of the first meiotic division. Because this prophase takes about 22 days, the majority of spermatocytes seen in sections will be in this phase. 93
  • 94. Spermatogenesis • Each primary spermatocyte subsequently undergoes a reduction division-the first meiotic division-to form two haploid secondary spermatocytes, which are approximately half the size of primary spermatocytes. 94
  • 95. • Subsequently, the secondary spermatocytes undergo a second meiotic division to form four haploid spermatids, which are approximately half the size of secondary spermatocytes. 95
  • 96. • The meiotic process therefore results in the formation of cells with a haploid number of chromosomes. • With fertilization, the normal diploid number is again attained. 96
  • 97. 97
  • 98. 98
  • 99. 99
  • 100. Spermiogenesis – Spermiogenesis : is the final stage of production of spermatozoids. The spermatids are transformed into spermatozoa Definition : The process of transformation of spermatids into sperms. 100
  • 101. Male genital system  Spermatogenesis : 2 n 2 n 2 n 2 n 2 n 2 n 2 n 2 n 2 n Multiplication Phase PGC Mitotic division Spermatogonia (B) Spermatogonia (A) 101
  • 102. Male genital system  Spermatogenesis : Growth Phase Spermatogonia (B) Spermatogonia (A) Undergo growth Mitotic division reserve type 102
  • 103. Male genital system  Spermatogenesis : Maturation Phase Undergo growth 2n n n Primary spermatocyte 1st meiotic division Secondary spermatocyte (2nd meiotic devision) 103
  • 104.  Spermatogenesis : Spermiogenesis n n Secondary spermatocyte (2nd meiotic devision) n n n n Sperm 104
  • 105. Spermiogenesis • Spermiogenesis is a complex process that includes 1. Formation of the acrosome (Gr. akron, extremity, + soma, body) 2. Condensation and elongation of the nucleus, 3. Development of the flagellum, and 4. Loss of much of the cytoplasm. 105
  • 106. Spermiogenesis • Spermiogenesis can be divided into three phases. The Golgi Phase The Acrosomal Phase The Maturation Phase 106
  • 107. Golgi phase • Prominent Golgi complex near the nucleus, mitochondria, a pair of centrioles, free ribosomes, and tubules of smooth endoplasmic reticulum. 107
  • 108. • proacrosomal granules • acrosomal granule • acrosomal vesicle. • The centrioles • The flagellar axoneme 108
  • 109. The Acrosomal Phase • The acrosomal vesicle spreads to cover the anterior half of the condensing nucleus and is then known as the acrosome • The acrosome contains several hydrolytic enzymes • dissociate cells of the corona radiata and • digest the zona pellucida, 109 hyaluronidase, neuraminidase, acid phosphatase, and a protease
  • 110. The acrosome hyaluronidase, neuraminidase, acid phosphatase, and a protease that has trypsin-like activity 110
  • 111. The Acrosomal Phase • One of the centrioles grows concomitantly, forming the flagellum. • Mitochondria aggregate around the proximal part of the flagellum, forming a thickened region known as the middle piece 111
  • 112. The Maturation Phase • Residual cytoplasm is shed and phagocytosed by Sertoli cells, and • the spermatozoa are released into the lumen of the tubule 112
  • 113. 113
  • 114. Spermatogenesis • The end result is the mature spermatozoon, which is then released into the lumen of the seminiferous tubule 114
  • 115. • Mature sperms are free-swimming, actively motile cells consisting of 115
  • 116. The Sperm • The sperm consists of a head, neck, body and tail.  The head • The Head contains 2 main parts (the nucleus and the acrosome) both have two basic functions of the sperm (genetic and activating respectively ). – The nucleus occupies most of the available space of sperm head and its shape determines the shape of the head of the sperm. It contains only its haploid complement of DNA. – The acrosome contains hydrolytic enzymes as hyaluronidase and acrosine 116
  • 117. The Sperm  Mid-piece • connected to head with a neck .(contain mitochondria ). 117
  • 118. The Sperm  Tail • Its function is movement of the sperm to swim with head foremost . – The sperm cell is totally devoid of stored food (yolk) and protective envelope. it is also devoid of most cytoplasm organelles such as ribosomes and endoplasmic reticulum. 118
  • 119. The Sperm 1 . Plasma membrane 2 . Outer acrosomal membrane 3 . Acrosome 4 . Inner acrosomal membrane 5 . Nucleus 6 . Proximal centriole 7 . Rest of the distal centriole 8 . Thick outer longitudinal fibers 9 . Mitochondrion 10. Axoneme 11. Anulus 12. Ring fibers A. Head B. Neck C. Mid piece D. Principal piece E. Endpiece Mature sperm 119
  • 120. The Sperm  Semen  Source :  it is ejaculated during the male sexual act. It is composed from the fluids from the vas deferens , the seminal vesicles , the prostate gland and the Cowper’s gland . The major bulk of the semen is seminal vesicle fluid (60%)  The average ph is approximately 7.5 120
  • 121. The Sperm  Semen  Content :  The usual quantity of semen ejaculated averages approximately 3.5 ml and in each ml. of semen is an average of 120 million sperms.  In normal persons , this number can vary from 35 millions to 200 millions . therefore an average of 400 million . Sperms are usually present in each ejaculate . When the number of sperms in each ml falls below approximately 20 million sperms , The person is likely to be infertile . 121
  • 122. • Of the 200 to 300 million spermatozoa deposited in the vagina, only 300 to 500 reach the ovum • Only one sperm fertilizes the ovum. • Other spermatozoa aid the fertilizing sperm in penetrating the ovum barriers by their enzymes. • Only capacitated sperm pass freely through corona radiata 122
  • 123. The Sperm  Transport of sperms – Sperms are non motile while they lie inside the male genital tract , but become motile after ejaculation in the vagina . By the undulating movement of their tails which act as propellers , The sperms ascend in the cervical canal and reach the cavity of the uterus . They are capable of swimming against the current produced by the cilia of the uterus . Few reach The uterine tubes where fertilization takes place . 123
  • 124. The Sperm  Viability of sperms – The sperms discharged in the female genital tract can remain a live and motile . However , the period during which they are able to fertilize the egg (i.e. viable) is variable . It is believed that the sperms remain viable for (1-2)days only . Note :  Human sperms were preserved alive in vitro for 2 weeks . 124
  • 125. The Sperm  Abnormalities of sperms  Numerical abnormalities a. Azo spermia (Aspermia ): No sperms at all , is found in the semen . b. Oligosperms : the number of sperms is few in the semen c. Necrospermia : the sperms are found dead 125
  • 126. The Sperm  Abnormalities of sperms  Morphological abnormalities  The head and the tail may be abnormal , they may be: a. Giants b. Dwarfs c. Some times , sperms are joined in head or in tail d. No tail 126
  • 127. The Sperm  Abnormalities of sperms  Sperms with morphological abnormalities lack motility and don’t fertilize the egg. 127
  • 128. Embryology Gametogenesis (Formation of gametes ) Spermatogenesis=Formation of sperms (Male reproductive system) testis Oogenesis=Formation of Ova (Female reproductive system) ovary 128
  • 129. The female reproductive system  The ovary:  Is the female sex gland . It lies in the ovarian fossa in the side wall of the pelvis . Its function is production of ova . It secretes two hormones: a. Estrogen (sex hormone): responsible for appearing of 2nd female sex characters . This hormone is secreted from Graffian follicle . b. Progesterone (pregnancy hormone):responsible for maintenance of pregnancy by increase the thickness and vascularity of uterine endometrium . This hormone is secreted from corpus luteum after ovulation process . 129
  • 130. The female reproductive system  The uterus:  In which the fetus develop . It lies between the bladder anteriorly and the rectum posteriorly .  is a thick-walled, pear-shaped muscular organ averaging 7 to 8 cm in length, 5 to 7 cm in width at its superior part, and 2 to 3 cm in wall thickness  The uterus consists of two major parts .Body, the expanded superior two thirds Fundus Isthimus .Cervix, the cylindrical inferior one third Cervical canal Internal os External os 130
  • 131. • The walls of the body of the uterus consist of three layers Perimetrium, the thin external layer Myometrium, the thick smooth muscle layer Endometrium, the thin internal layer 131
  • 132. The perimetrium • is a peritoneal layer that is firmly attached to the myometrium. • outer serosa (connective tissue and mesothelium) or adventitia (connective tissue). 132
  • 133. The Myometrium the thick smooth muscle layer 133
  • 134. Endometrium • During the luteal (secretory) phase of the menstrual cycle, three layers of the endometrium can be distinguished microscopically : compact layer spongy layer basal layer 134
  • 135. compact layer • A thin, compact layer consisting of densely packed, connective tissue around the necks of the uterine glands 135
  • 136. spongy layer • A thick, spongy layer composed of edematous connective tissue containing the dilated, tortuous bodies of the uterine glands 136
  • 137. basal layer • A thin, basal layer containing the blind ends of the uterine glands • At the peak of its development, the endometrium is 4 to 5 mm thick. • The basal layer of the endometrium has its own blood supply and is not sloughed off during menstruation. 137
  • 138. functional layer • The compact and spongy layers, known collectively as the functional layer, disintegrate and are shed during menstruation and after parturition (delivery of a baby). 138
  • 140. 140
  • 141. The female reproductive system  Uterine (fallopian tube ): – In which fertilization , cleavage takes place . – It is lined with secretory epithelium for nourishment of ovum . – By its cilliary movement , muscle contraction help picking up of ovum from ovary . – approximately 10 cm long and 1 cm in diameter – extend laterally from the horns (L., cornua) of the uterus 141
  • 142. Parts uterine tube the infundibulum, the ampulla, the isthmus, and the uterine part. 142
  • 143. The female reproductive system Female reproductive system 143
  • 144. Function of U.T • carry oocytes • Sperms (ampulla of the uterine tube ) • conveys the cleaving zygote to the uterine cavity. 144
  • 145. OOGENESIS Oogenesis (ovogenesis) is the sequence of events by which oogonia are transformed into mature oocytes. • This maturation process begins before birth and is completed after puberty. • Oogenesis continues to menopause, which is permanent cessation of the menses (bleeding associated with the menstrual cycles). 145
  • 147. Stage of ooginesis 1. prenatal maturation 2. postnatal maturation 147
  • 148. 1. prenatal maturation • Around the end of the first month primordial germ cells migrates from the yolk sac to the gonadal primordia. • In the gonads these cells divide and transform into oogonia. 148
  • 149. 1. prenatal maturation • Division is so intense that • 2nd -600,000 oogonia, • 5th - >>>7 million. 149
  • 152. 1. prenatal maturation • During early fetal life(3rd month), oogonia proliferate by mitosis. • Oogonia enlarge to form primary oocytes before birth • As a primary oocyte forms, connective tissue cells surround it and form a single layer of flattened, follicular epithelial cells • The primary oocyte enclosed by this layer of cells constitutes a primordial follicle. 152
  • 153. 1. prenatal maturation • Primary oocytes begin the first meiotic division before birth. But instead of proceeding into metaphase They enter diplotene stage of of meiosis I. (Diplotene stage-resting stage during prophase) 153
  • 154. 1. prenatal maturation • The follicular cells (flat) are believed to secrete a substance, oocyte maturation inhibitor, which keeps the meiotic process of the oocyte arrested. Prophase The primary oocytes remain dormant in the ovarian follicles until puberty. 154
  • 155. 1. prenatal maturation By 7th.month • Majority of Oogonia (as well as primary oocytes) degenerate • Most of the Serviving Primary Oocytes (at prophase of meiosis I.) are individually surrounded by a layer of flat epithelial cells & form Primodial follicle (primary oocyte with a layer of flat epithelial cells) 155
  • 156. Postnatal Maturation of Oocytes • As the primary oocyte enlarges during puberty, the follicular epithelial cells become cuboidal in shape and then columnar, forming a primary follicle. • The primary oocyte soon becomes surrounded by a covering of amorphous acellular glycoprotein material, the zona pellucida. • Scanning electron microscopy of the surface of the zona pellucida reveals a regular meshlike appearance with intricate fenestrations. 156
  • 157. Postnatal Maturation of Oocytes • As a follicle matures, the primary oocyte increases in size and, shortly before ovulation, completes the first meiotic division to give rise to a secondary oocyte and the first polar body. • Unlike the corresponding stage of spermatogenesis, however, the division of cytoplasm is unequal. 157
  • 158. Postnatal Maturation of Oocytes • The polar body is a small, nonfunctional cell that soon degenerates. • At ovulation, the nucleus of the secondary oocyte begins the second meiotic division, but progresses only to metaphase, when division is arrested. Zonar pellucida Secondary oocyte First polar body 158
  • 159. Postnatal Maturation of Oocytes • primary oocytes in the ovaries • two million newborn • no more than 40,000 adolescence • Of these, only approximately 400 become secondary oocytes and are expelled at ovulation during the reproductive period. • Few of these oocytes, if any, are fertilized and become mature. 159
  • 160. Postnatal Maturation of Oocytes • Beginning during puberty, usually one follicle matures each month and ovulation occurs 160
  • 161. 161
  • 162. The ovum  The ovum resembles any ordinary cell in its structure . It is large oval cell which varies from (117-142) μ in diameters . 162
  • 163. The ovum  Coverings : a. 2 membranes :an inner thin delicate one called vitelline membrane and an outer thick transparent membrane called zona pellucida . b. Corona radiata: 2 or 3 layers of cells which surround the zona pellucida when the ovum is shed from follicle . 163
  • 165. 165
  • 166. The ovum  Significance of egg membranes: a. provide the protection to the contents of egg b. Prevent polyspermia i.e. Fertilization by more than one sperm . c. Maintain the normal cleavage of the egg. 166
  • 167. FEMALE REPRODUCTIVE CYCLES Commencing at puberty, females undergo reproductive cycles (sexual cycles), involving activities of the hypothalamus of the brain, pituitary gland (L., hypophysis), ovaries, uterus, uterine tubes, vagina, and mammary glands. • These monthly cycles prepare the reproductive system for pregnancy. 167
  • 168. FEMALE REPRODUCTIVE CYCLES • Ovarian cycle • Time during which development of follicles, ovulation, and corpus luteum formation • Menstrual (endometrial) cycle • monthly changes in the internal layer of the uterus 168
  • 169. 169
  • 170. 170
  • 171. Hormonal changes At puberty & Ovarian cycle • Hypothalamus produces hormone • - gonadotropin releasing ( GnRH. ) • GnRH. Acts on Ant. Pituitary • Ant.Pit. --- Secretes FSH.& LH. • -these hormones stimulate & control cyclical changes in ovary • the Ovarian cycle started • -cyclical changes in ovary starting from the onset of puberty 171
  • 172. 172 LH
  • 173. Hormones ( produced by Ant.Pituitary & Ovary) at Puberty Hypothalamus produces Gonadotropin-releasing hormone (GnRH)… Anterior Pituitary produces FSH. & LH. Ovary produces Fr.Follicular/ Theca cells Oestrogen Corpus luteum Progesterone 173
  • 174. Ant.Pit. --- Secretes FSH.& LH. (FSH) stimulates the development of ovarian follicles and the production of estrogen by the follicular cells. (LH) serves as the "trigger" for ovulation (release of secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone. 174
  • 175. OVARIAN CYCLE • FSH and LH produce cyclic changes in the ovaries-the ovarian cycle Which include A. development of follicles, B. ovulation and C. corpus luteum formation. 175
  • 176. A. Follicular Development Development of an ovarian follicle is characterized by: - Growth and differentiation of primary oocyte - Proliferation of follicular cells - Formation of zona pellucida - Development of the theca folliculi 176
  • 177. A. Follicular Development 1. primordial follicles—consist of a primary oocyte enveloped by a single layer of flattened follicular cells 177
  • 178. A. Follicular Development 2. primary follicle Follicular cells divide by mitosis and form a single layer of cuboidal cells; the follicle is then called a unilaminar primary follicle Early primary follicle 178
  • 179. A. Follicular Development • Follicular cells continue to proliferate and form a multilaminar primary or preantral follicle 179
  • 180. A. Follicular Development • A thick amorphous layer, the zona pellucida, surrounds the oocyte. • Filopodia of follicular cells and microvilli of the oocyte penetrate the zona pellucida and make contact with one another via gap junctions. 180
  • 181. A. Follicular Development 3. secondary or antral follicles Liquid (liquor folliculi) begins to accumulate between the follicular cells. The small spaces that contain this fluid coalesce, and the granulosa cells reorganize themselves to form a larger cavity, the antrum . • The follicles are then called secondary or antral follicles. Glycosaminoglycans, progesterone, androgens, and estrogens 181
  • 182. A. Follicular Development • Cells concentrated at a certain point on the follicular wall forms a small hillock of cells, the cumulus oophorus, that protrudes toward the interior of the antrum and contains the oocyte . • A group of granulosa cells concentrates around the oocyte and forms the corona radiata. These granulosa cells accompany the oocyte when it leaves the ovary. 182
  • 183. A. Follicular Development • the fibroblasts of the stroma immediately around the follicle differentiate to form the theca folliculi (theca from Greek, meaning box). • This layer subsequently differentiates into the theca interna and the theca externa 183
  • 184. A. Follicular Development • The theca soon differentiates into two layers, an internal vascular and glandular layer, the theca interna, and a capsule-like layer, the theca externa. 184
  • 185. A. Follicular Development • Thecal cells are thought to produce an angiogenesis factor that promotes growth of blood vessels in the theca interna, which provide nutritive support for follicular development. 185
  • 186. A. Follicular Development • The dominant follicle may reach the most developed stage of follicular growth—the mature, preovulatory, or graafian follicle— and may ovulate. Preovulatory Graafian follicle 186
  • 187. 3. Pre-ovulatory stage i. formation of Graffian follicle about 37 hours b/f ovulation Antrum - enlarges considerably Oocyte -pushed to one side & embeded in a mound of cumulus oophorus Graffian Follicle -with antrum &-cumulus oophoricus 187
  • 188. Maturation of Ovum in each cycle A. changes in Follicle -In each Cycle 15-20 Primodial follicles grow & pass thro’ i.Primary follicle(preantral) ii.Secondary follicle (antral) iii.Graafian follicle (preovulatory) but only One follicle b/c • Mature follicle • FSH. is necessary for maturation of Primary follicles to antral & preovulatory stages • LH.(increase in mid cycle) causes • i.secondary follicle to enter preovulatory stage • Secondary follicle grows rapidly to diameter of 25mm. Under the influence of FSH. & LH. Primodial follicle Primary follicle Secondary follicle antrum Graafia n follicle Granul osa cells zona pelucida Cumulus oophorus 188
  • 189. A. Follicular Development • The early development of ovarian follicles is induced by FSH, but final stages of maturation require LH as well. • Growing follicles produce estrogen, 189
  • 190. A. Follicular Development • Estrogen regulates development and function of the reproductive organs. • The vascular theca interna produces follicular fluid and some estrogen. Its cells also secrete androgens that pass to the follicular cells, which, in turn, convert them into estrogen. 190
  • 191. Oocyte changes at preovulatory stage cont… • With a surge in LH matured follicle (usually one) enters • 3.Preovulatory stage B. formation of Secondary oocyte • -Primary oocyte (arrested in diplotene stage of 1st.meiotic division) enter metaphase (A) • (B) -Secondary oocyte is formed after completion of meiosis I. • (C) -Secondary oocyte enters meiosis II.(arrested at metaphase) Granulosa cells Secondary oocyte in meiosis ii. Primary oocyte in meiosis( I ). A Secondary oocyte & polar bdy 1 B C 191
  • 192. B Ovulation • Defination • -process in which secondary oocyte is released from the ovary • Time of Ovulation • -14 day before next menstruation • (for woman with regular • 28 days cycle) 192
  • 193. B Ovulation • Around midcycle, the ovarian follicle, under the influence of FSH and LH, undergoes a sudden growth spurt, producing a cystic swelling or bulge on the surface of the ovary. • A small avascular spot, the stigma, soon appears on this swelling. • Before ovulation, the secondary oocyte and some cells of the cumulus oophorus detach from the interior of the distended follicle. 193
  • 194. Ovulation Surface bulge stigma 1.High level of estrogen to - hypothalamus & Ant.pituitary LH. surge Ovary Ovulation occurs 194 Ovulation is triggered by a surge of LH production. Ovulation usually follows the LH peak by 12 to 24 hours. The LH surge, elicited by the high estrogen level in the blood, appears to cause the stigma to balloon out, forming a vesicle. The stigma soon ruptures, expelling the secondary oocyte with the follicular fluid.
  • 195. B Ovulation • The expelled secondary oocyte is surrounded by the zona pellucida and one or more layers of follicular cells, which are radially arranged as the corona radiata, forming the oocyte-cumulus complex. 195
  • 196. B Ovulation • The LH surge also seems to induce resumption of the first meiotic division of the primary oocyte. • Hence, mature ovarian follicles contain secondary oocytes 196
  • 197. C Corpus Luteum • Shortly after ovulation, Under LH influence, the walls of the ovarian follicle and theca folliculi collapse and are thrown into folds they develop into a glandular structure, the corpus luteum 197
  • 198. corpus luteum secretes progesterone and  some estrogen, • causing the endometrial glands to secrete and prepare the endometrium for implantation of the blastocyst. 198
  • 199. Type of corpus luteum 1. corpus luteum of pregnancy : 2 corpus luteum of menstruation 199
  • 200. corpus luteum of pregnancy : 1. If the oocyte is fertilized, the corpus luteum enlarges to form a corpus luteum of pregnancy and increases its hormone production. • Degeneration is prevented by human chorionic gonadotropin. • 20 weeks of pregnancy. • the placenta 200
  • 201. 2. corpus luteum of menstruation no fertilization, the corpus luteum involutes and degenerates 10 to 12 days after ovulation. transformed into white scar tissue in the ovary, a corpus albicans. 201
  • 202. Duration of ovarian cycle • Ovarian cycle persist • throughout the reproductive life of women and terminate at menopause, the permanent cessation of menstruation, usually between the ages of 48 and 55. • No ovarian cycle • during pregnancy • menopause 202
  • 203. Menstrual (Endometrial) Cycle • is the time during which the oocyte matures, is ovulated, and enters the uterine tube. • The hormones produced by the ovarian follicles and corpus luteum (estrogen and progesterone) produce cyclic changes in the endometrium. 203
  • 204. Menstrual (Endometrial) Cycle • The average menstrual cycle is 28 days, with day 1 of the cycle designated as the day on which menstrual flow begins 204
  • 205. Phases of menstrual cycle 205 Menstrual Phase. Proliferative phase Luteal Phase 4 to 5 days 9 days 13 days
  • 206. Phases of menstrual cycle 1. Menstrual Phase. (lasts 4 to 5 days) The functional layer of the uterine wall is sloughed off and discarded blood + endometrium= After menstruation, the eroded endometrium is thin. 206
  • 207. Phases of menstrual cycle 2. Proliferative Phase. The proliferative (follicular, estrogenic) phase ~ 9 days coincides with growth of ovarian follicles and is controlled by estrogen secreted by these follicles. • two- to-three fold increase in the thickness of the endometrium and in its water content • Early during this phase, the surface epithelium reforms and covers the endometrium. • The glands increase in number and length, and the spiral arteries elongate. 207
  • 208. Phases of menstrual cycle 3 Luteal Phase. The luteal (secretory, progesterone) phase, ~ 13 days, coincides with the formation, functioning, and growth of the corpus luteum. 208
  • 209. Luteal phase • The progesterone produced by the corpus luteum stimulates the glandular epithelium to secrete a glycogen-rich material. • The glands become wide, tortuous, and saccular, and the endometrium thickens because of the influence of progesterone and estrogen from the corpus luteum and because of increased fluid in the connective tissue.. • As the spiral arteries grow into the superficial compact layer, they become increasingly coiled. • The venous network becomes complex and large lacunae (venous spaces) develop. • Direct arteriovenous anastomoses are prominent features of this stage 209
  • 210. What happen to emdometrium cycle if 210
  • 211. If fertilization does not occur • The corpus luteum degenerates.  Estrogen and progesterone levels fall and  The secretory endometrium enters an ischemic phase. • Menstruation occurs. 211
  • 212. If fertilization occurs • Cleavage of the zygote and blastogenesis (formation of blastocyst) occur. • The blastocyst begins to implant on approximately the sixth day of the luteal phase (day 20 of a 28-day cycle). • Human chorionic gonadotropin, keeps the corpus luteum secreting estrogens and progesterone. • The luteal phase continues and menstruation does not occur. 212
  • 214. Oocyte transport Ovary to in infudibulum  The sweeping action of the fimbriae (move back and forth over the ovary) and  fluid currents produced by the cilia of the mucosal cells of the fimbriae "sweep" the secondary oocyte 214
  • 216. TRANSPORTATION OF GAMETES • infudibulum to ampulla • peristalsis-movements of the wall of the tube characterized by alternate contraction and relaxation-that pass toward the uterus. 216
  • 217. Oocyte transport i.fimbra sweep over the Ovary, & tube contracts ii.Oocyte with cumu pulled into the tube by fimbrae mment iii.Cilia sweep Oocyte • t/w Ut. • Note: • -cumulus lose contact • with oocyte once gets • in the tube 217
  • 218. TRANSPORTATION OF GAMETES • Sperm Transport • In male reproductive tract • Epididymis The urethra The accessory sex produce secretions that are added to the sperm. • Ejaculated sperm • external os & the fornix of the vagina during sexual intercourse. 218
  • 219. The reflex ejaculation of semen two phases: • Emission: • Epd-to-the prostatic part of the urethra ----peristalsis of the ductus deferens • Ejaculation • from the urethra through the external urethral orifice; this results from closure of the vesical sphincter at the neck of the bladder, contraction of urethral muscle, and contraction of the bulbospongiosus muscles. 219
  • 220. Sperm Transport in FRT • external os ----cervical canal By movements of their tails. • Why against?????? • The enzyme vesiculase, produced by the seminal glands, coagulates some of the semen or ejaculate and forms a vaginal plug that may prevent the backflow of semen into the vagina. • When ovulation occurs, the cervical mucus increases in amount and becomes less viscid, making it more favorable for sperm transport. 220
  • 221. Sperm Transport in In FRT • Cervical canal through the uterus to uterine tubes mainly from muscular contractions of the walls of these organs. • Prostaglandins in the semen • stimulate uterine motility at the time of intercourse and assist in the movement of sperms to the site of fertilization in the ampulla of the tube. • Fructose, secreted by the seminal glands, is an energy source for the sperms in the semen. 221
  • 222. 1. The volume of sperm or ejaculate (sperms suspended in secretions from accessory sex glands) averages 3.5 mL, with a range of 2 to 6 mL. 2. Mov’t speed 2-3 mm/min slow- in the acid environment of the vagina more rapid in the alkaline environment of the uterus 3. Duration 1. 5 minutes after their deposition near the external uterine os. 2. Some sperms, however, take as long as 45 minutes to complete the journey. 4. No of sperm that reach the Ampula Only approximately 200 sperms reach the fertilization site. Most sperms degenerate and are resorbed by the female genital tract. 222
  • 223. MATURATION OF SPERMS • In most species, Freshy ejaculated spermatozoa are not capable of fertilization immediately upon entering the female reproductive tract • Sperm must undergo capacitation before they are fertilized Definition: • Morphologic, physiologic, and biochemical changes which occur to the sperm result in sperm capable of penetrating through the corona radiate and zona pellucid of the ovum. (removal of macro-molecular material from the sperm surface) 223
  • 224. MATURATION OF SPERMS Freshy ejaculated sperm must undergo • a .Capacitation-utrus &FT • b .Acrosomal reaction • a. Capacitation • Definition - process in which changes occur in Sperm during its passage thro’female reproductive tract - Changes (during Capacitation) are. - removal of the following from plasma membr. - fr. Plasma membr.of Sperm overlying Acrosome - i. glycoprotein coat - ii. seminal plasma protein - Duration: - -last for about 7 hours 224
  • 225. Capacitation of the sperm • Is a period of sperm conditioning in the female genital tract; mainly in the uterine tube & it takes about 7 hrs. • It entails epithelial interaction between the sperm and mucosal surface of the tube resulting in: - Removal of a glycoprotein coat and seminal plasma proteins from plasma membrane overlying the acrosomal region of spermatozoa. • Only capacitated sperm pass through corona cells & undergo acrosome reaction.
  • 226. Effects of Capacitation on Sperm • Increased rate of metabolism • Flagellum beats more rapidly; Result: Sperm are more motile • Changes in sperm plasmalemma proteins allow sperm-egg binding and occurrence of the acrosome reaction • Pro-Acrosin (inactive) is converted to acrosin (active) • Sperm become capable of chemotaxis 226
  • 227.
  • 228. b.Acrosomal reaction The acrosomal cap contains several enzymes like acid phosphatase, hyaluronidase, which are involved in penetration of the oocyte. Just before approaching the oocyte, the capacitated sperm head establishes multiple contacts and discharges the chemical substances in succession to overcome the barriers around the oocyte. This process of multiple contacts is known as acrosome reaction. Zona pellucida. Perivitellin e space Acrosom e 228
  • 229. Acrosome contains 2 enzymes • Hyaluronidase (corona penetrating enzymes) Protein that breaks down mucopolysaccharides Mucopolysaccharides (hyaluronic acid) is the material that holds the cumulus oopherus cells together. • Acrosin This enzyme plus sperm flagellum aid in penetrating to the perivitelline space 229
  • 230. 230
  • 231. Note the following • Oocyte • It takes about 72 hours for an egg to reach the uterus • If it is to survive, an egg must be fertilixed within 12 to 24 hours for an egg to reach the uterus. • Therefore, in order to fertilize the egg before it dies, sperm must encounter it somewhere in the distal one-third of the uterine tube. 231
  • 232. Sperm • spermatozoa can reach the distal uterine tube within 5-10minutes of ejaculation, but they cannot fertilize an egg for about 10hours. • most sperm are fertile for a maximum of 48hours after ejaculation, so there is little chance of ferilizing an egg if intercourse occurs more than 48 hours before ovulation 232
  • 233. Viability of gametes • human oocytes are usually fertilized within 12 hours after ovulation(12-24hours). • Most human sperms probably do not survive for more than 48 hours in the female genital tract. 233
  • 234. • Of the 200 to 300 million spermatozoa deposited in the vagina, only 300 to 500 reach the ovum • Only one sperm fertilizes the ovum. • Other spermatozoa aid the fertilizing sperm in penetrating the ovum barriers by their enzymes. • Only capacitated sperm pass freely through corona radiata 234
  • 235. Viability of Oocyte &Spermatozoa • Oocyte after ovulation • -24 hours • Spermatozoa after ejaculation • -48 hours • (or may remain viable for several • days in female reproductive tract) • 3 days“Window” better chance for fertilization • b/t.2days b/f. & 1 day after Ovulation 235
  • 237. 237
  • 238. 238
  • 239. 239
  • 240. FERTILIZATION • Defnition • Fertilization is a complex sequence of coordinated molecular events that begins with contact between a sperm and an oocyte and ends with the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of the zygote, a unicellular embryo 240
  • 242. • -Ampullary region • -widest & (longest) • ampulla Ampulla Where does ferti. usually take place ? Why? Uterus Uterine tube 242
  • 243. Zygote A zygote is a highly specialized, totipotent cell that marks the beginning of each of us as a unique individual. 243
  • 244. zygote 244 The unicellular zygote divides many times and becomes progressively transformed into a multicellular human being through cell division, migration, growth, and differentiation.
  • 245. Results of fertilization 1. Restoration of the diploid numbers of chromosomes half from the father and half from the mother . Hence the zygote contains a few combination of chromosomes different from both parents . 2. Determination of the sex of the new individual . An X-carrying sperm will produce a female (XX) embryo , and a Y – carrying sperm will produce a male (XY)embryo . Hence .the chromosomal sex of the embryo . is determined at fertilization.  Chromosome Y contains TDF (Testis determining factor ). 245
  • 246. Results of fertilization 3. The characters , state of health or disease and the features derived father and mother are determined by fertilization and carried to the fetus . 4. Initiation of cleavage : without fertilization , The Oocyte usually degenerates 24 hours after ovulation. 246
  • 247. Cleavage, Blastosis & Implantation 247
  • 248. Cleavage Is a series of repeated mitotic divisions that results in an increase in the number of cells. 248
  • 250. Cleavage • Zygote: • 2-cell stage • 4-cell stage • 8-cell stage • 16-cell stage (morula) Late blastocyst Early blastocyst trophoblasts cavity Inner cell mass morula 8 cells stage 2 cell stage 4 cell stage pellucida
  • 251.
  • 254. 254
  • 255. Compaction After the nine-cell stage, the blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells 255
  • 256. Importance of compaction Compaction permits greater cell-to-cell interaction and is a prerequisite for segregation 256
  • 257. Blastocyst • When does morula • Enter Uterine cavity? • About 4 days aft.ferti. • Formation of Blastocyst • As the morula enters Ut.cavity(4 days) • fluid secreted by endometrial glands (uterine milk) enters morula • Fluid filled cavity- Blastocele • Morula b/c Blastocyst 4 days A. B. C. 257 Pass through zona pellucida
  • 258. Formation of the blastocyst 258
  • 259. 259
  • 260. Blastomeres & derivatives What are the Blastomeres? What are their derivatives? Inner cell mass which will later gives rise to embryo K/s. Embryoblast Outer cell mass k/s-Trophoblast - placenta formation - Production of Human chorionic gonadotropin
  • 261. Blastocyst cont.. • Zona pellucida,is it still necessary? • By 5th.day • A hole is formed in Z.pellucida (by an enzyme) • Blastocyst then squeezes thro’ the hole • rapidly increase in size • Now blastocyst (devoid of investments) is ready for Implantation •
  • 262. 262
  • 264. 264
  • 265. Formation of the hypoblast At approximately 7 days 265
  • 266. 266
  • 267. 267
  • 268. Chronology of Ovum (aft.Ovulation) 14th.day b/f next menstrua. Within 24Hrs.after Ovulation • 4 days after fertilization • 6th. Day after fertilzation • What happen to • -Blastomeres? • -Blastocele ? Day 5. Day 6.
  • 269. 269
  • 270. 270
  • 271. Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast Week Two Bilaminar Germ Disc Hypoblast
  • 272. Day Eight – Bilaminar Disc Inner Cell Mass (embryoblast) Trophoblast Blastocele
  • 273. Day Eight – Bilaminar Disc • Mitotic figures • Cells in the cytotrophoblast divide and migrate into the syncytiotrophoblast, where they fuse and lose their individual cell membranes.
  • 274. Day Eight – Bilaminar Disc • Cells of the inner cell mass or embryoblast also differentiate into two layers: (a) a layer of small cuboidal cells the hypoblast layer; and (b) a layer of high columnar cells epiblast layer • Together, the layers form a flat disc.
  • 275. Day Eight – Bilaminar Disc • a small cavity appears within the epiblast. • This cavity enlarges to become the amniotic cavity. Soon amniogenic (amnion-forming) cells-amnioblasts-separate from the epiblast and form the amnion, which encloses the amniotic cavity
  • 276.
  • 277. 277
  • 278. Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast
  • 279. Day Nine • defect in the surface epithelium is closed by a fibrin coagulum. • vacuoles appear in the syncytium. When these vacuoles fuse, they form large lacunae, and this phase of trophoblast development is thus known as the lacunar stage.
  • 280. Primitive yolk sac Day Nine flattened cells probably originating from the hypoblast form a thin membrane, the exocoelomic (Heuser’s) membrane
  • 281. Exocoelomic cavity: formed when cells from the hypoblast line the cytotrophoblast Will soon become the primary yolk sac and then the secondary yolk sac Day Nine
  • 282. Day Nine Extraembryonic coelom / chorionic cavity: formed by large cavities in the extraembryonic mesoderm
  • 283. Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Primary Yolk Sac Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast
  • 284. Day Eleven & Twelve • the blastocyst is completely embedded in the endometrial stroma, and • the surface epithelium covers the original defect • The trophoblast is characterized by lacunar spaces in the syncytium
  • 285. Day Eleven & Twelve • sinusoids • The syncytial lacunae become continuous with the sinusoids, and maternal blood enters the lacunar system. • As the trophoblast continues to erode more and more sinusoids, maternal blood begins to flow through the trophoblastic system, establishing the primordial uteroplacental circulation.
  • 286. Day Eleven & Twelve • a new population of cells(derived from yolk sac cells) appears between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity. • Primitive yolk sac
  • 287. Day Eleven & Twelve • Development of extraembryonic coelom, • Except where the germ disc is connected to the trophoblast by the connecting stalk .
  • 288.
  • 289. 289
  • 290. 290
  • 291. Day Thirteen – More stuff happens -the hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane. -These cells proliferate and gradually form a new cavity within the exocoelomic cavity. - -This new cavity is known as the secondary yolk sac or definitive yolk sac. -This yolk sac is much smaller than the original exocoelomic cavity, or primitive yolk sac. --During its formation, large portions of the exocoelomic cavity are pinched off. These portions are represented by exocoelomic cysts, which are often found in the extraembryonic coelom or chorionic cavity. Extraembryonic coelom expands and forms the chorionic cavity Connecting stalk: where extraembryonic mesoderm traverses through the chorionic cavity. Develops into the umbilical cord.
  • 293.
  • 294. Day Thirteen – More stuff happens • the extraembryonic coelom expands and forms a large cavity, the chorionic cavity. • The extraembryonic mesoderm lining the inside of the cytotrophoblast is then known as the chorionic plate.
  • 295. Day Thirteen and Fourteen • primary chorionic villi. • The prechordal plate develops as a localized thickening of the hypoblast,
  • 296. Sadler, Langman´s Medical Embryology, 2004 Microphotography: Heuser CH, Rock J, Hertig AT: Contrib Embryol Carnegie Instn, Wash 31:85, 1945 13-day implanted human blastocyst Extraembryonic mesoderm somatic (somatopleuric): attached to the trophoblast – chorionic plate (3) attached to the amnioblasts (4)- amnion splanchnic (splanchnopleuric) attached to the endoderm of the yolk sac (6) exocoelomic cyst (2) Primary chorionic villi Maternal sinusoid Prechordal plate Trophoblast lacunae Extraembryonic coelom (1) Chorionic cavity Trophoblast lacunae 2 1 Amnionic cavity (AC) AC Secondary yolk sac (sYS) sYS Connecting stalk 3 4 6
  • 297. So far – three cavities Amniotic Cavity • Will eventually surround the embryo after folding Secondary Yolk Sac • Formerly primary yolk sac, which was formerly the exocoelomic cavity Chorionic Cavity • Formerly EXTRAembryonic coelom
  • 299. Ectopic Pregnancy Implantation of blastocysts usually occurs in the endometrium of the uterus, superior in the body of the uterus, slightly more often on the posterior than on the anterior wall.
  • 300. Definition Failure of implantation of a fertilized ovum inside the endometrial cavity. OR Development of the pregnancy outside its normal place for implantation. 300
  • 301. Cause 1) Previous Tubal Infections 2) Previous Tubal or Pelvic Surgery 3) Hormonal Factors- interfere with normal tubal motility of the fertilized ovum 4) Contraceptive Failure- interfere with normal tubal motility of the fertilized ovum 5) Stimulation of Ovulation- stimulating drugs for ovulation- These drugs alter the estrogen/progesterone level, which can affect tubal motility 6) Infertility Treatment (with in vitro fertilization (IVF) or gamete intrafallopian transfer (GIFT) since underlying tubal damage is frequently one of the causative factors predisposing one to this type of infertility treatment.) 7) Environmental Effect- Maternal cigarette smoking at the time of conception was found in a case-controlled study, to be associated with an increased risk of an ectopic pregnancy 8) Transmigration of Ovum Migration of the ovum from one ovary to the opposite fallopian tube can occur by an extrauterine or intrauterine route. This can cause a potential delay in transportation of the fertilized ovum to the uterus. Then trophoblastic tissue is present on the blastocyst before it reaches the uterine cavity, and therefore the trophoblastic tissue implants itself on the wall of the fallopian tube. 301
  • 302. Sites of ectopic pregnancy Tubal pregnancy Most common type of ectopic pregnancy with most common location being the ampulla Ampullary 80% Isthmic 12% Fimbrial end 5% Cornoal and interstitial 2% 1/10/2024 302 SFB
  • 303. 303
  • 304. Sites of ectopic pregnancy Abdominal Pregnancy (1.4%) Implantation occurs in the peritoneal cavity Primary Directly in the abdominal cavity Secondary Secondary to tubal rupture and abortion Ovarian pregnancy(.2%) One that develops in the ovary (criteria for diagnosis: gestational sac occupies normal location of the ovary, sac connected to the uterus by uteroovarian ligament, ipsilateral tube intact, ovarian tissue in the wall of the 304
  • 305. Cervical pregnancy(.2%) In the cervical canal below the internal os 305 In very rare cases the fertilized ovum bypasses the uterine endometrium and implants itself in the cervical mucus.
  • 306.
  • 307. 307
  • 308. Quick Summary • Fertilised egg cleaves and implants • Bilaminar disc forms (epiblast and hypoblast) • Cavities start forming (amniotic, yolk sac, chorionic)
  • 309. Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Yolk Sac Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast Ectoderm Mesoderm Endoderm GASTRULATION
  • 310. The second week of development is known as the week of twos: the trophoblast – (the cytotrophoblast and syncytiotrophoblast.) The embryoblast- ( the epiblast and hypoblast). The extraembryonic mesoderm – ( the somatopleure and splanchnopleure). Two cavities-the amniotic and yolk sac cavities, form.
  • 312. Gastrulation The process that establishes all three germ layers in the embryo.
  • 313. What contribute to gastrulation? 315
  • 314. Extensive cell shape changes, Rearrangement, Movement, and Changes in adhesive properties contribute to the process of gastrulation.
  • 315. Epiboly Convergent extension movement of sheets of cells which tend to cover other cells
  • 316.
  • 317.  Rapid development of the embryo from the embryonic disc during the third week is characterized by  Appearance of primitive streak (the first sign of gastrulation)  Development of notochord  Differentiation of three germ layers
  • 319. 325 Thickened linear band the primitive stre
  • 320.
  • 321.
  • 322. As soon as the primitive streak appears, it is possible to identify the embryo's craniocaudal axis, its cranial and caudal ends, its dorsal and ventral surfaces, and its right and left sides. The primitive groove and pit result from the invagination (inward movement) of epiblastic cells-Mesenchymal
  • 323.
  • 324. Shortly after the primitive streak appears, cells leave its deep surface and form mesenchyme, Mesenchyme is a tissue consisting of loosely arranged cells suspended in a gelatinous matrix. Mesenchymal cells are ameboid and actively phagocytic . Mesenchyme forms the supporting tissues of the embryo, such as most of the connective tissues of the body and the connective tissue framework of glands. Some mesenchyme forms mesoblast (undifferentiated mesoderm), which forms the intraembryonic, or embryonic, mesoderm . Cells from the epiblast ,the primitive node and other parts of the primitive streak displace the hypoblast, forming the embryonic endoderm in the roof of the umbilical vesicle. The cells remaining in the epiblast form the embryonic ectoderm.
  • 325. • Mesenchymal cells (pluripotential cells) derived from the primitive streak migrate widely and proliferate and differentiate into diverse types of cells, such as fibroblasts, chondroblasts, and osteoblasts . • In summary, cells of the epiblast, through the process of gastrulation, give rise to all three germ layers in the embryo, the primordia of all its tissues and organs.
  • 326. Fate of the Primitive Streak • The primitive streak actively forms mesoderm by the ingression of cells until the early part of the fourth week; thereafter, production of mesoderm slows down. • The primitive streak diminishes in relative size and becomes an insignificant structure in the sacrococcygeal region of the embryo. • Normally the primitive streak undergoes degenerative changes and disappears by the end of the fourth week.
  • 327. Female infant with a large sacrococcygeal teratoma that developed from remnants of the primitive streak Persistence of primitive streak that proliferates and forms new growth at the sacrococcyg eal area
  • 328. Sperm and secondary oocyte Pronuclei Morula Inner Cell Mass Outer Cell Mass Embryoblast Epiblast Hypoblast Yolk Sac Blastocyst Trophoblast Cytotrophoblast Syncytiotrophoblast Ectoderm Mesoderm Endoderm
  • 330. median cellular cord, the notochordal process
  • 331.
  • 332.
  • 333.
  • 334.
  • 335. NOTOCHORDAL PROCESS AND NOTOCHORD • Prechordal mesoderm(b/n PP &NP) - essential in forebrain and eye induction. • The prechordal plate have a role as a signaling center for controlling development of cranial structures.
  • 336. Function of The notochord 1. Defines the primordial longitudinal axis of the embryo and gives it some rigidity 2. Provides signals that are necessary for the development of axial musculoskeletal structures and the central nervous system 3. Contributes to the intervertebral discs 4. Degenerates as the bodies of the vertebrae form, but small portions of it persist as the nucleus pulposus of each intervertebral disc. 5. The developing notochord induces the overlying embryonic ectoderm to thicken and form the neural plate, the primordium of the central nervous system (CNS).
  • 337. Migration of mesenchym and mesodermal cell From primitive streak and notochordal process 352
  • 338. 353
  • 339. 354
  • 340. 355
  • 341. 356
  • 342. Migration of mesenchym and mesodermal cell 1. laterally and cranially-- margins of the embryonic disc. --Continuous EE mesoderm
  • 343. Cranially On each side of the notochordal process and around the prechordal plate 358
  • 344. 359
  • 345. Migration of mesenchym and mesodermal cell • By the middle of the third week, intraembryonic mesoderm separates the ectoderm and endoderm everywhere except  At the oropharyngeal membrane cranially  In the median plane cranial to the primitive node, where the notochordal process is located  At the cloacal membrane caudally
  • 347. THE ALLANTOIS • The allantois appears on ~ day 16 as a small, sausage-shaped diverticulum (outpouching) from the caudal wall of the umbilical vesicle that extends into the connecting stalk
  • 348. Allantois -It appears on day 16 from caudal end of yolk sac into connecting stalk. -It is involved with early blood formation and associated with urinary bladder development. -It becomes urachus and remains as median umbilical ligament Yolk sac Connecting stalk  umbilical cored
  • 349.
  • 350. NEURULATION FORMATION OF THE NEURAL TUBE 368
  • 351. - The processes involved in the formation of the neural plate, neural folds and closure of the folds to form the neural. - It is completed by the end of the 4th week ,when closure of the caudal neuropore occurs. - The embryo is called neurula during neurulation.
  • 352. Neural Plate and Neural Tube 370
  • 353. 371
  • 354. 372
  • 355. Gastrulation to neurulation Neural plate Precordal plate Neural plate Notochordal plate
  • 356.
  • 357.
  • 358.
  • 359.
  • 361.
  • 362. Formation of Neural Crest Cells Neural tube Notochord Melanocytes Schwann cells; Meninges (pia, arach) Cells of suprarenal medulla Autonomic ganglion cells Surface ectoderm Cranial sensory ganglion cells Posterior root ganglion cells Neural crest 388 forms sensory ganglia of spinal (dorsal root ganglia), cranial nerves (V, VII, IX, X) and ganglia of the autonomic nervous system V, VII, IX, X
  • 363.
  • 364.
  • 365. Secondary neurulation - Neuropores close: -Cranial neuropore (day 24)  forebrain -Caudal neuropore (day 26)  somite 31(S2) -Mesodermal caudal eminence  neural cord  neural tube Neural tube (CNS) and neural crest (PNS) derived from ectoderm Caudal neural tube derived form mesoderm
  • 368. 401
  • 369. 402
  • 371. Paraxial mesoderm is organized, cephalocaudally, into segments known as: – Somitomeres: more loosely organized in the head region forming in association with segmentation of the neural tube into neuromeres – Somites: more compact and defined regions forming from the occipital region caudally; first somite forms on the 20th day, and last pair at the end of the 5th week
  • 372. Somite period of human development
  • 373. About 38 pairs of somites form during the somite period of human development (days 20 to 30). By the end of the fifth week, 42 to 44 pairs of somites are present
  • 374. E21 days E22 days E24 days
  • 375. By the end of the fifth week, 42 to 44 pairs of somites are present
  • 376. Somites ( 44 Pairs) They are- 4 Occipital 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral Coccygeal 8-10 • Later 1st Occipital and last 5 -7 Coccygeal disappear
  • 377. Fate of the Somites Each somite can be divided into two main portions: sclerotome and dermomyotome; it also receives its own segmental nerve component The sclerotome is the ventromedial portion of the somite which forms a loosely organized tissue (the mesenchyme) and migrates around the notochord and spinal cord, forming the vertebral column, in addition to forming tendons for its muscles
  • 378. Intermediate Cell Mass Mesoderm Intermediate mesoderm (nephrogenic cord) differentiates into urogenital Structures (kidney, testis & ovary)
  • 379. Lateral Plate Mesoderm:  spaces appear in it & fuse forming a U- shaped cavity (intraembryonic coelom), formed of 3 parts:  2 longitudinal pleuro- peritoneal canals: gives 2 pleural & 2 peritoneal cavities.  A transverse cranial part: gives pericardial sac.
  • 380. Lateral Plate Mesoderm The lateral plate mesoderm is divided into: Parietal (somatic) layer facing the ectoderm. Together they form the intraembryonic somatopleure. it gives the muscles and connective tissue of the ventral & lateral body wall Visceral (splanchnic) layer facing endoderm. Together they form the intraembryonic splanchnopleure. It gives the smooth muscles of the viscera (gut).
  • 381. The Cranial Part Of Intra- embryonic Mesoderm • The cardiogenic plate: • Cranial to the oral membrane a condensation of intra- embryonic mesoderm is present & called the cardiogenic plate which will give rise to the heart. • The septum transversum: • Cranial to the cardiogenic plate, there is another mass of intra-embryonic mesoderm is called septum transversum which forms the future diaphragm.
  • 382. DEVELOPMENT OF THE INTRAEMBRYONIC COELOM -Intraembryonic coelom (cavity) --fusion of isolated coelomic spaces in the lateral mesoderm and cardiogenic mesoderm into a horseshoe-shaped cavity. -Lateral mesoderm divided into: -A somatic or Parietal layer--together with extraembryonic mesoderm covering amnion and ectoderm called somatopleure, embryonic body wall (upper side) -A splanchnic or Visceral layer--together with extraembryonic mesoderm covering yolk sac and endoderm is called splanchnopleure, embryonic gut wall (lower side) -During the 2nd month, intraembryonic coelom is divided into 3 body cavities: 1. pericardial cavity 2. pleural cavities 3. peritoneal cavity
  • 383.
  • 384.
  • 385. Dr: Azza ZAki Differentiation Of The Endoderm
  • 386. Differentiation Of The Endoderm • 1-The Gut: • The endoderm initially is a flat layer of cells covering the surface of the embryonic disc that faces the yolk sac. • With the formation of the head & tail folds, parts of the yolk sac become enclosed within the embryo. A tube lined by endoderm is formed (primitive gut) from which most of gastrointestinal tract is formed.
  • 387. The part of the gut cranial to communication with the yolk sac is called the foregut& the part caudal to this communication is called the hindgut while the intervening part is called the midgut. The midgut is associated with the yolk sac via the vitelline duct.
  • 388. Communication Of The Gut: The mouth begins as a depression on the surface ectoderm called stomodeum. This is separated from the foregut by the buccopharyngeal membrane which ruptures. The proctodeum is a depression of the surface ectoderm at the tail end of the embryo. This is separated from the hindgut by the cloacal membrane which ruptures.
  • 389. Derivatives Of The Endoderm  Epithelial lining of the alimentary tract.  Epithelium of the glands develop from the alimentary tract; the thyroid, parathyroid, liver& pancreas. • The epithelium lining of the respiratory tract (trachea, bronchi &lung).
  • 390. Derivatives Of The Endoderm • Epithelial lining of the urinary bladder. • Epithelial lining of the pharyngeotympanic tube ,tympanic cavity and mastoid antrum • Tonsil.
  • 391. EARLY DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM
  • 392. WHY early cardiovascular system ? • The urgent need for blood vessels to bring oxygen and nourishment to the embryo from the maternal circulation through the placenta. • During the third week, a primordial uteroplacental circulation develops
  • 393. EARLY DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM Embryonic Nutrition 2nd week -maternal blood by diffusion through the extraembryonic coelom and umbilical vesicle. 3rd week, vasculogenesis and angiogenesis (Gr. angeion, vessel + genesis, production), or blood vessel formation, begins in the extraembryonic mesoderm of the umbilical vesicle, connecting stalk, and chorion.
  • 394.
  • 395. Vasculogenesis and Angiogenesis The formation of the embryonic vascular system involves two processes: 1. Vasculogenesis is the formation of new vascular channels by assembly of individual cell precursors called angioblasts. 2. Angiogenesis is the formation of new vessels by budding and branching from preexisting vessels.
  • 396. Blood vessel formation (vasculogenesis) in the embryo and extraembryonic membranes during the third week may be summarized as follows
  • 397. • The first blood islands appear in mesoderm surrounding the wall of the yolk sac at 3 weeks of development and slightly later in lateral plate mesoderm and other regions
  • 398.
  • 399. • These islands arise from mesoderm cells that are induced to form hemangioblasts, a common precursor for vessel and blood cell formation. • Hemangioblasts in the center of blood islands form hematopoietic stem cells, the precursors of all blood cells, whereas peripheral hemangioblasts differentiate into angioblasts, the precursors to blood vessels. These angioblasts proliferate and are eventually induced to form endothelial cells .
  • 400. 441
  • 401. Blood and Blood vessels • Hemangioblasts- are derived from mesenchymal cells • Central cells become primitive blood cells and peripheral cells form endothelial cells of blood vessels
  • 404. • Mesenchymal cells (mesoderm derived) differentiate into endothelial cell precursors- angioblasts (vessel-forming cells), which aggregate to form isolated angiogenic cell clusters called blood islands, • Small cavities appear within the blood islands and endothelial cords by confluence of intercellular clefts.
  • 405. • Angioblasts flatten to form endothelial cells that arrange themselves around the cavities in the blood island to form the endothelium. • These endothelium-lined cavities soon fuse to form networks of endothelial channels (vasculogenesis). • Vessels sprout into adjacent areas by endothelial budding and fuse with other vessels.
  • 406. Angiogenesis • Once the process of vasculogenesis establishes a primary vascular bed, which includes the dorsal aorta and cardinal veins, additional vasculature is added by angiogenesis, the sprouting of new vessels
  • 407.
  • 409. Embryonic vessels first form mainly in the aorta-gonad-mesonephros area; then in the liver; then the definitive hematopoietic area, the bone marrow
  • 410. The Primitive Circulation The heart begins beating at the beginning of the forth week; the cardiovascular system is the first functional system to develop
  • 411. Hematopoietic stem cells of Hemangioblasts Central cells 452
  • 412. • Cavities appear within the blood island; central cells become hematopoietic stem cells (the ancestor of all types of blood cells) 453
  • 414. Transitory As mentioned, the first blood cells arise in the blood islands of the yolk sac, but this population is transitory. 455
  • 416. • The definitive hematopoietic stem cells arise from mesoderm surrounding the aorta in a site called the aorta-gonad-mesonephros region (AGM). • These cells will colonize the liver, which becomes the major hematopoietic organ of the fetus. Later, stem cells from the liver will colonize the bone marrow, the definitive blood-forming tissue. 457
  • 417. Fused dorsal aortae from 4th thoracic somite to 4th lumbar somite Dorsal aortae 1st aortic arch Aortic sac Heart tube
  • 418. The mesenchymal cells surrounding the primordial endothelial blood vessels differentiate into the muscular and connective tissue elements of the vessels.
  • 419. The Primordial Cardiovascular System the heart -The heart and great vessels form from mesenchymal cells in the cardiogenic area.
  • 420. Early development of Heart and BV Angioblastic cords Heart tubes Endocardial tubes
  • 421.
  • 422.
  • 423. Primordial cardiovascular system -The tubular heart joins with blood vessels in the embryo, connecting stalk, chorion, and umbilical vesicle to form a 464
  • 424. • The cardiovascular system is the first organ system to reach a functional state.
  • 425. • The embryonic heartbeat can be detected using Doppler ultrasonography during the fifth week, approximately 7 weeks after the last normal menstrual period.
  • 426. DEVELOPMENT OF CHORIONIC VILLI • Shortly after primary chorionic villi appear at the end of the second week, they begin to branch. • Early in the third week, mesenchyme grows into these primary villi, forming a core of mesenchymal tissue. The villi at this stage-secondary chorionic villi-cover the entire surface of the chorionic sac
  • 427.
  • 428. Sadler, Langman´s Medical Embryology, 2004 Microphotography: Heuser CH, Rock J, Hertig AT: Contrib Embryol Carnegie Instn, Wash 31:85, 1945 13-day implanted human blastocyst Extraembryonic mesoderm somatic (somatopleuric): attached to the trophoblast – chorionic plate (3) attached to the amnioblasts (4)- amnion splanchnic (splanchnopleuric) attached to the endoderm of the yolk sac (6) exocoelomic cyst (2) Primary chorionic villi Maternal sinusoid Prechordal plate Trophoblast lacunae Extraembryonic coelom (1) Chorionic cavity Trophoblast lacunae 2 1 Amnionic cavity (AC) AC Secondary yolk sac (sYS) sYS Connecting stalk 3 4 6
  • 429. • Some mesenchymal cells in the villi soon differentiate into capillaries and blood cells. • They are called tertiary chorionic villi when blood vessels are visible in them. The capillaries in the chorionic villi fuse to form arteriocapillary networks, which soon become connected with the embryonic heart through vessels that differentiate in the mesenchyme of the chorion and connecting stalk.
  • 430. • Capillaries in tertiary villi make contact with capillaries developing in mesoderm of the chorionic plate and in the connecting stalk . • These vessels, in turn, establish contact with the intraembryonic circulatory system, connecting the placenta and the embryo. • Hence, when the heart begins to beat in the fourth week of development, the villous system is ready to supply the embryo proper with essential nutrients and oxygen.
  • 431.
  • 432. • By the end of the third week, embryonic blood begins to flow slowly through the capillaries in the chorionic villi. • Oxygen and nutrients in the maternal blood in the intervillous space diffuse through the walls of the villi and enter the embryo's blood. Carbon dioxide and waste products diffuse from blood in the fetal capillaries through the wall of the chorionic villi into the maternal blood.
  • 433. cytotrophoblastic cells cytotrophoblastic shell, which gradually surrounds the chorionic sac and attaches it to the endometrium. Villi that attach to the maternal tissues through the cytotrophoblastic shell are stem chorionic villi (anchoring villi). Those that branch from the sides of stem villi are free (terminal) villi, through which exchange of nutrients and other factors will occur
  • 434. • The villi that grow from the sides of the stem villi are branch chorionic villi (terminal villi). It is through the walls of the branch villi that the main exchange of material between the blood of the mother and the embryo takes place. The branch villi are bathed in continually changing maternal blood in the intervillous space.