Fertilization is the union of a sperm and an egg to form a zygote. There are two types: external fertilization, where gametes are released into the environment, and internal fertilization, which occurs in nearly all terrestrial animals. For internal fertilization to occur, sperm must undergo a process of transport and capacitation to prepare for fertilizing the egg. Upon fertilization, a series of cellular events take place to prevent polyspermy, including cortical reaction, acrosomal reaction, and nuclear reaction, leading to the formation of a diploid zygote.
INTRODUCTION
DEFINATION
GAMETES
STRUCTURE OF GAMETES
SPERM
OVUM
RECOGNITION OF EGG AND SPERM
CAPACITATION
ACROSOME REACTION
SPECIES-SPECIFIC RECOGNITION
GAMETE BINDING AND RECOGNITION
GAMETE FUSION
PREVENTION OF POLYSPERMY
ACTIVATION OF GAMETE METABOLISM
FUSION OF THE GENETIC MATERIAL
SIGNIFICANCE OF FERTILIZATION
CONCLUSIONS
REFERENCES
Polyspermy describes an egg that has been fertilized by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy
The first issue that an egg and a sperm of any organism type face in successfully producing an embryo is the possibility of polyspermy. Polyspermy is the fertilization of an egg by multiple sperm, and the results of such unions are lethal.
If multiple sperm fertilize an egg, the embryo inherits multiple paternal centrioles. This causes competition for extra chromosomes and results in the disruption of the creation of the cleavage furrow, thus causing the zygote to die. As an important model organism in the study of fertilization and embryonic development, polyspermy in sea urchins has been studied in detail. The sea urchin’s methods of polyspermy prevention have been broken down into two main pathways. These two primary pathways are known as the fast block and the slow block to polyspermy
After the sperm’s receptors come into contact with the egg’s jelly layer and the acrosomal enzymes are released and break down the jelly layer, the sperm head comes into contact with the vitelline and plasma membranes of the egg. When the two plasma membranes contact one another, signals in the egg are initiated.
First, Na+ channels in the egg open, allowing Na+ to flood into the egg. This causes a depolarization of the egg from it’s normal resting potential of -70 mV.
While depolarization is occurring, the remainder of the jelly layer is dissolving. With the dissolution of the jelly layer and the depolarization of the plasma membrane, the first block to preventing fertilization by multiple sperm is put into place.
These two simple changes are part of the first block to polyspermy, known as the fast block. Within 1/10th of a second of contact, the fast block t
INTRODUCTION
DEFINATION
GAMETES
STRUCTURE OF GAMETES
SPERM
OVUM
RECOGNITION OF EGG AND SPERM
CAPACITATION
ACROSOME REACTION
SPECIES-SPECIFIC RECOGNITION
GAMETE BINDING AND RECOGNITION
GAMETE FUSION
PREVENTION OF POLYSPERMY
ACTIVATION OF GAMETE METABOLISM
FUSION OF THE GENETIC MATERIAL
SIGNIFICANCE OF FERTILIZATION
CONCLUSIONS
REFERENCES
Polyspermy describes an egg that has been fertilized by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy
The first issue that an egg and a sperm of any organism type face in successfully producing an embryo is the possibility of polyspermy. Polyspermy is the fertilization of an egg by multiple sperm, and the results of such unions are lethal.
If multiple sperm fertilize an egg, the embryo inherits multiple paternal centrioles. This causes competition for extra chromosomes and results in the disruption of the creation of the cleavage furrow, thus causing the zygote to die. As an important model organism in the study of fertilization and embryonic development, polyspermy in sea urchins has been studied in detail. The sea urchin’s methods of polyspermy prevention have been broken down into two main pathways. These two primary pathways are known as the fast block and the slow block to polyspermy
After the sperm’s receptors come into contact with the egg’s jelly layer and the acrosomal enzymes are released and break down the jelly layer, the sperm head comes into contact with the vitelline and plasma membranes of the egg. When the two plasma membranes contact one another, signals in the egg are initiated.
First, Na+ channels in the egg open, allowing Na+ to flood into the egg. This causes a depolarization of the egg from it’s normal resting potential of -70 mV.
While depolarization is occurring, the remainder of the jelly layer is dissolving. With the dissolution of the jelly layer and the depolarization of the plasma membrane, the first block to preventing fertilization by multiple sperm is put into place.
These two simple changes are part of the first block to polyspermy, known as the fast block. Within 1/10th of a second of contact, the fast block t
cell commitment and differentiation, stem cell,types of differentiationshallu kotwal
The commitment of cells to specific cell fates and their capacity to differentiate into particular kinds of cells.
Cellular differentiation is the process in which a cell changes from one cell type to another. Usually, the cell changes to a more specialized type. Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover.
Vittelogenesis is a word developed from Latin vitellus-yolk, and genero-produce
Vitellogenesis (also known as yolk deposition) is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction of lecithotrophic organisms. In insects, it starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein.
Yolks is the most usual form of food storage in the egg.
Yolks appear in the oocyte in the secondary period of their growth called vittelogenesis.
Thus,the formation and deposition of yolks is known as vittelogenesis
Characteristic
Yolks is a complex variable assembled component.
The principle component are protein,phospholipid and fats in different combination.
Depending upon these component yolks is distinguished into protein yolks and fatty acid
For eg- the avian contain 48.19% water , 16.6 % protein, 32.6% phospholipids and fats and 1% carbohydrates.
Slides about Cell Fate, Cell Potency, Differentiation, Specification, Modes of Specification, Role of Cytoplasm. Cell Interactions, Regulation in Development
cell commitment and differentiation, stem cell,types of differentiationshallu kotwal
The commitment of cells to specific cell fates and their capacity to differentiate into particular kinds of cells.
Cellular differentiation is the process in which a cell changes from one cell type to another. Usually, the cell changes to a more specialized type. Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover.
Vittelogenesis is a word developed from Latin vitellus-yolk, and genero-produce
Vitellogenesis (also known as yolk deposition) is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction of lecithotrophic organisms. In insects, it starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein.
Yolks is the most usual form of food storage in the egg.
Yolks appear in the oocyte in the secondary period of their growth called vittelogenesis.
Thus,the formation and deposition of yolks is known as vittelogenesis
Characteristic
Yolks is a complex variable assembled component.
The principle component are protein,phospholipid and fats in different combination.
Depending upon these component yolks is distinguished into protein yolks and fatty acid
For eg- the avian contain 48.19% water , 16.6 % protein, 32.6% phospholipids and fats and 1% carbohydrates.
Slides about Cell Fate, Cell Potency, Differentiation, Specification, Modes of Specification, Role of Cytoplasm. Cell Interactions, Regulation in Development
USMLE GENERAL EMBRYOLOGY 008 First week of development A embryo .pdfAHMED ASHOUR
The initial week of embryonic development is a vital period commencing with fertilization, leading to the creation of the zygote and early cell divisions. It's noteworthy that, throughout this week, the developing embryo remains in the pre-implantation stage, journeying from the fallopian tube toward the uterus. Key events such as fertilization, cleavage, and the formation of the blastocyst are crucial for the embryo's early development.
These events lay the foundation for subsequent processes in the following weeks. The successful implantation of the blastocyst into the uterus marks the transition from the first week to the second week of embryonic development.
3 GEN EMBRYOLOGY third Week 3 germ layer .pptxAkhilaV16
third wk there is formation of three germ layers. primitive streek and prochordal plate forms the intra embyyonic mesoderm. the epiblast cells replace all the 3 germ layers. iem is converted to paraxial, intermediate and lateral plate mesoderms
1. COLLEGE OF HEALTH SCIENCE
DEPARTMENT OF PHYSIOLOGY
ADVANCED REPRODUCTIVE PHYSIOLOGY
Molecular BASIS OF
FERTILIZATION
By TEKETEL ERISTU
1Molecular Basis of Fertilization
3. Objectives
At the end of the presentation you will be able to:
Define Fertilization
Know the types of Fertilization
Describe Cellular Events
Explain Sperm Transport and Capacitation
Discuss ovum reaction to Sperm Penetration
3Molecular Basis of Fertilization
5. 23
46
46 23
23
23
23
23 46
sperm
mother
cell
ovum
mother
cell
sperms produced
by meiosis
fertilization
zygote
ova produced by meiosis
but only one develops to
maturity
46 46
46 46
46 46 4646
46 46 46 46
4646
46 46
4646
Early EmbryoFertilization:
Union of a Spermatozoal nucleus, of
paternal origin, with an egg nucleus, of
maternal origin, to form the primary nucleus
of an embryo.
5Molecular Basis of Fertilization
7. Types of Fertilization
1.External Fertilization:
is common in aquatic animals
Parents release their gametes into the environment
7Molecular Basis of Fertilization
8. Internal Fertilization
occurs in nearly all terrestrial animals
Sperm are deposited in or close to the female
reproductive tract
Gametes unite within the tract following mating
CONT….
8Molecular Basis of Fertilization
9. 1.3 Cellular Events
a) Ovum Maturation
Cell
Type
Ploidy Process Process Completion
Oogoniu
m
diploid Oocytogenesis
(mitosis)
3rd trimester (forming
Oocytes)
Primary
Oocyte
diploid Ootidogenesis
(Meiosis 1)
(Folliculogenesis)
Halts in prophase 1
Seconda
ry Ocyte
haploid Ootidogenesis
(Meiosis 2)
Halted in metaphase 2
untill fertilization
Ovum haploid 9Molecular Basis of Fertilization
10. CONT…
2N (diploid) cell replicates its
DNA, resulting in a 4N cell
(meiosis I)
2N cells
(meiosis II)
1N (haploid) cells
10Molecular Basis of Fertilization
11. b) TransportThree Stages:
• 1. Ovulation
Expulsion of the oocyte
Captured the Ciliated fimbriated end of the fallopian tube
The Ciliary action and Peristaltic waves of oviduct
musculature bring the ovum into the ampulla of the
fallopian tube
Fertilization Normally occurs in the ampulla ( ampulary-
isthmic junction) of fallopian tube and Usually within 24 hrs
of after ovulation.
Cont...
11Molecular Basis of Fertilization
12. CONT…
b.Transportation (utero-tubal Junction, junction b/n Uterus and
Oviduct) and Implantation of the Zygote
C.Utetro tubal junction uterine cavity
12Molecular Basis of Fertilization
13. Cont….
1. Follicle in Ovary is ready
to ovulate
2. New corpus Luteum
3. Ovulated Ovum in the
second meiotic division
4. Formation of second
polar body after
fertilization
5. Fusion of egg and sperm
Pronuclear; and
6. Beginning of first mitotic
division of zygote.
13Molecular Basis of Fertilization
14. 1.4 Sperm Transport and Capacitation
a. Transport:
• Velocity = 1-4mm/min (300 x106 200 sperms reach the oviduct).
• Flaggelar movement (to-and-fro) + ATP
The sperm are first deposited in the vagina:
they then pass up this cavity and through the cervix into the uterus ,
up the uterus, through the junction between the uterus and oviduct
(Uterotubal Junction), and up the isthmus of the oviduct to the usual
area of fertilization in the oviduct: the ampullary –isthmic junction.
14Molecular Basis of Fertilization
15. Cont…
1.Vaginal Sperm
After about one minute of deposition in the Vagina
the semen becomes thicker and less liquid
( Coagulation).
After about 20 minutes, the semen again liquefies,
Stimulates some sperm to swim more rapidly.
15Molecular Basis of Fertilization
16. Cont…
• The environment in the vagina is usually acidic
( about PH 4.2) and this level of acidity inhibit semen
motility.
The presence of semen in the vagina, however,
increases the vaginal PH to a basic 7.2, which in turn
increase sperm motility.
16Molecular Basis of Fertilization
17. Cont…
2. Cervical Sperm
The cervical canal is lined by a complicated series
of narrow folds and crypts and
is blocked by a sticky mass of cervical mucus and
tiny cervical fibers.
Estrogen cause the mucus to become more liquid
and makes gaps wider.
17Molecular Basis of Fertilization
18. CONT…
• The cervical fibers vibrate in rhythm with the tail
beat frequency of normal sperm,
this may allow the normal sperm to move through the
cervix;
where as sperm with abnormal or absent tail beats
are detained.
Other sperms enter cervical Crypts, where they may
die or lost or they remain as a reservoir of sperm
that may enter the uterus.
18Molecular Basis of Fertilization
19. Cont…
3. Uterine Sperm
Upon leaving the cervix, the sperm travel up the
uterus to the uterotubal junction.
The uterus fluid is watery but sparse
The swimming rate of sperm (3mm/min) cannot
account to climb up uterine lumen.
19Molecular Basis of Fertilization
20. The muscle contraction and movement of cilia in the
female reproductive tract that facilitate sperm
transport.
Uterotubal junction allows the gradual entrance of
sperm in the isthmus of the oviduct.
About half of the sperm enter the wrong oviduct and
only a few hundred make it to the general proximity
of the waiting egg.
CONT..
20Molecular Basis of Fertilization
22. b.Capacitation
• Sperms cannot fertilize oocytes when they are newly
ejaculated. Thus Capacitation
• Is a process of sperm becoming fertile
• a process of essential changes in the spermatozoa that
enables them to fertilize the egg.
• occurs during transport in female genital tract
• capacitated sperm have the ability to fertilize the egg
• The process of capacitation takes 5-7 hours.
22Molecular Basis of Fertilization
23. Major Changes in sperm cell membrane during Capacitation
Changes in surface glycoproteins, caused by secretion of FGT
Cholesterol is removed- increase Fluidity
Glycoproteins are lost- expose zona binding proteins
Proteins are phosphorylated
Fluctuations occur in the intracellular levels of calcium ions-
essential for hyperactivation.
Cont.
23Molecular Basis of Fertilization
24. Effects of Capacitation on Sperm
• Increased rate of metabolism
• Hyperactivation: flagellum beats more rapidly
• Changes in sperm glycoproteins allow sperm egg binding
• Pro-Acrosin (inactive) is converted to acrosin (active)
CONT….
24Molecular Basis of Fertilization
25. 1.5 Ovum Reaction to sperm penetration
• Zona Binding
• Zona proteins: ZP1, ZP2, ZP3
• Initiates acrosome reaction
a) Acrosomal Reaction
After binding to the corona radiata the
sperm reaches the zona pellucida.
Sperm head binds to a ZP2 glycoprotein in the zona pellucida.
This binding triggers the acrosome to burst, releasing
enzymes that help the sperm get through the zona
pellucida. 25Molecular Basis of Fertilization
26. Cont…
The acrosome reaction is associated with the release of
acrosome enzymes that facilitate fertilization
Acrosomal enzymes: esterases, acrosin,hyaluronidase ,and
neuraminidase cause lysis of the zona pellucida
26Molecular Basis of Fertilization
27. On binding sperm is induced to undergo the acrosomal reaction (ZP3)
Influx of Ca2+ into the sperm cytosol
Contents of the acrosome are released (+ exocytosis)
i. Proteinases/acrosin) + hyaluronidase penetration of ZP.
ii. Exposes other proteins on the sperm surface that bind to ZP2 help
the sperm maintain the binding to zona
iii.Exposes a protein in the sperm plasma membrane that mediates the
binding and fusion of this membrane with that of the egg.
• Penetration thru ZP 15-25min.
27Molecular Basis of Fertilization
32. B. Cortical Reaction
• Once sperm penetrates zona pellucida, the zona
reaction occurs:
– This reaction makes the zona pellucida impermeable to
other sperms.
• Egg Activation
• Cortical Reaction
– exocytosis of cortical granules
• Zona block
-biochemical changes eliminates
sperm binding
This prevents fertilization of an
egg by more than one sperm. 32Molecular Basis of Fertilization
33. Mechanisms:
Two mechanisms can operate to ensure that only one sperm
fertilizes the egg.
1.Primary block to polyspermy
Rapid depolarization of the egg plasma membrane
prevents further sperm from fusing and
thereby acts as a fast primary block to polyspermy.
But the membrane potential returns to normal soon after
fertilization, so that a second mechanism is required to
ensure a longer-term, secondary block to polyspermy
Cont…
33Molecular Basis of Fertilization
34. ii. Secondary block to polyspermy
• A local increase in cytosolic Ca2+ (spreads in a wave).
• prolonged Ca2+ oscillations.
• Activate the egg to begin development,
• The cortical granules release their contents by exocytosis
Proteolytic cleavage of ZP2 and the hydrolysis of sugar
groups on ZP3
• The zona becomes “hardened,” so that sperm no longer
bind to it.
CONT…
34Molecular Basis of Fertilization
36. C. Nuclear Reaction
• Cortical reaction pulls the sperm nucleus.
• Loses the membrane that surround the head.
• Tail incorporated into the egg cytoplasm.
• Naked nucleus male pronucleus
• Approaches haploid nucleus of the ovum female
pronucleus
• Male pronucleus + female pronucleus diploid zygote
• GENOME of a NEW ORGANISM… mitotic process….36Molecular Basis of Fertilization
37. 2 References
1. Human Reproductive Biology Richard
E.JONES, 3rd edition.
2. Advanced Reproductive Physiology Lecture
notes, Dr. Getahun
3. Different internet Sources
37Molecular Basis of Fertilization
