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Human Reporduction Topics 6.6&11 reprod
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Human Reporduction Topics 6.6&11 reprod






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Human Reporduction Topics 6.6&11 reprod Human Reporduction Topics 6.6&11 reprod Presentation Transcript

  • Human Reproduction Topic 6.6/11.4
  • Structure of the reproductive system
    • Male Reproductive System
  • Structure of the Testis
    • Each testis is composed of a tubular structure. It is from these seminiferous tubules where sperm are produced.
    • From puberty these tubules will produce sperm cells throughout the life of the man.
    • Note the basement membrane which surrounds each tubule.Inside the basement membrane can be seen various cells which are the stages of the developing spermatozoa.
  • Micrograph of testis
    • This light micrograph shows the cross section of seminiferous tubules, blood vessels and also the interstitial Leydig cells.
    • Leydig cells are responsible for the production of testosterone
    • Each testis is composed of a tubular structure. It is from these seminiferous tubules that sperm are produced.
    • From puberty these tubules will produce sperm cells throughout the life of the man.
    • Note the basement membrane which surrounds each tubule.
    • Inside the basement membrane can be seen various cells which are the stages of the developing spermatozoa.
    • Between the seminiferous tubules are groups of cells called interstitial or Leydig cells that produce the male sex hormone, testosterone.
    Please Sing a Song for Me
    • This image is of the wall of a seminiferous tubule.
    • a) Basement membrane
    • b) Germinal epithelium (2n) which divide by mitosis to produce
    • c) Spermatogonium (2n) which grow and enlarge
    • d) Primary spermatocytes (4n) go through Meioses I to Secondary Spermatocytes (2n). Secondary Spermatocytes go through Meiosis II to produce spermatids (n)
    • e) Sertoli cells nourish and allow the spermatids to differentiate to spermatozoa. These are released into the lumen
  • Spermatogenesis
  • Spermatogenesis
    • • Spermatogonium are found at or near the basement membrane.
    • • They have a high rate of cell division by mitosis to produce spermatogonia.
    • • Primary Spermatocytes are large diploid cells which form from rapidly growing spermatogonia.
    • • The Primary spermatocytes separate the homologous pairs of chromosomes in meiosis I(reduction division) to form the haploid Secondary Spermatocytes.
    • • The spermatids are formed from the separation of the sister chromatids in meiosis II.
  • Spermatogenesis
    • • The spermatids are found in association with the sertoli cells which nourish the spermatids as they differentiate into spermatozoa.
    • • The rate of spermatozoa is high and continuous throughout the life on the sexually mature male.
    • • The average number of spermatozoa in ejaculated semen is 32 x 10 6 ml -1
  • Spermatogenesis
  • Hormonal Control of Spermatogenesis
    • • There are two hormones secreted from the anterior pituitary FSH and LH.
    • • FSH stimulates the primary Spermatocytes which carry out meiosis I (reduction division) to separate homologous pairs of chromosomes and produce haploid secondary spermatocytes.
    • • LH stimulates the interstitial cells to produce testosterone
    • • Testosterone stimulates the maturation of secondary spermatocytes through meiosis and differentiation to spermatozoa.
  • Hormonal Control of Spermatogenesis
  • Structure of Sperm
    • • The acrosome vesicle contains the enzymes required to digest its way though the ovum wall.
    • • Haploid nuclei (n=23) containing the paternal chromosome set
    • • The 'mid-section' of the sperm contains many mitochondria which synthesis ATP to provide the energy for the movement of the tails structure.
    • • Protein fibers add longitudinal rigidity and provide a mechanism of propulsion.
  • Structure of Sperm
  • Semen production
    • Epididymis:
    • • Testicle fluids are removed and the sperm concentrated
    • • Sperm mature here and develop the ability to swim
    • Seminal vesicles:
    • • Adds nutrients that include fructose sugar for respiration
    • • Mucus to protect sperm in the cell
    • Prostate:
    • • Fluids that neutralize the vaginal acids and minerals ions
    • • Mineral ions
  • Semen production
  • Female Reproductive System (a) Ovary (b) Oviduct C Myometrium (d) Uterus (e) Cervix (f) Vagina (g) Endometrium
  • Female Reproductive System
  • Menstrual Cycle:
    • Sexual maturity in women is marked by the beginning of the menstrual cycles. These cycles coordinate the development and release of an egg with the conditions required in the uterus to support a pregnancy.
    • The cycle is controlled by hormones from both the brain and the ovary.
    • The natural cycle repeats until there is either a pregnancy or the woman reaches menopause and the end of the reproductive phase of her life.
    • FSH and LH are two hormone that are active at significant phases of human development including primary and secondary sexual characteristics. They are both significant hormones in the primary sex determination. Following puberty human become fertile and in females this is manifest as the menstrual cycle.
  • Anterior Pituitary Hormones:
    • Follicle Stimulating Hormone (FSH)
        • Stimulates the development of a primary follicles (oocytes).
        • Increases the number of follicular cells which in turn produce oestrogens.
        • Produces follicular fluids.
        • Develops the oocyte in the follicle
    • Luteunizing Hormone (LH):
        • surges in mid cycle (12 days) to bring about ovulation.
        • high LH is associated with a resumption of meiosis in the oocyte. Meiosis has been arrested in Prophase I since the embryonic stage. Only at the point of fertilization does meiosis complete.
        • stimulates the development of the corpus luteum.
  • Ovarian Hormones
    • Estrogen:
    • Stimulates the development of the endometrium (lining of the uterus) and it associated blood supply.
    • During the first half of the cycle there is positive feedback through increased sensitivity of the follicle cells to FSH (Up-regulation of receptors on the follicular cell plasma membrane).
    • During the second half of the cycle (high estrogen) there is negative feedback on FSH and LH.
    • Progesterone :
    • maintains the lining of the endometrium
    • negative feedback on FSH and LH
  • Menstrual Cycle
  • Menstrual Cycle:
    • A) Follicle Stimulating Hormone (FSH) is secreted by the pituitary gland of the brain and stimulates the development of a primary follicle.
    • B) Primary follicle cells secrete estrogen which in turn increase the secretion of FSH in a positive feedback.
    • C) The estrogen thickens the lining of the uterus in preparation for a fertilized egg.
    • D) The peak of estrogen secretion causes the pituitary to release a surge of LH. This loosens the now mature egg which is released in ovulation
    • • LH reduces the secretion of estrogen
    • • LH stimulates the empty follicle to develop into
    • the corpus luteum
  • Menstrual Cycle:
    • (e) Progesterone and estrogen together stop any more LH and FSH being secreted from the pituitary. (negative feedback)
    • • This prevents further follicle development or
    • ovulation.
    • (f) Progesterone maintains the lining of the thickened endometrium in preparation for the implantation of a fertilized egg.
    • (g) If implantation does not take place then the Corpus luteum degenerates and fails.
    • The progesterone production stops
          • • The endometrium breaks down and the menstrual
          • period begins
          • • The inhibition of FSH and LH by ovarian hormones
          • has been removed and so they begin their
          • secretions again of FSH.
          • • A new cycle has begun.
  • Ovary structure
    • A)Primary follicles in the medulla region (center) each one contains an oogonia arrested at prophase I.
    • b) Sequence showing the development of the primary follicle (PI) into the secondary follicle (MII).
    • c) The mature secondary follicle is also known as a graffian follicle. The size of this follicle will make the wall of the ovary bulge prior to ovulation. Note the exclusion of the 1 st polar body that will degenerate
    • d) Ovulation, with the rupture of the follicle wall the oocyte is released into the oviduct.
    • e) The Oocyte moves into the oviduct. This oocyte is at metaphase II and will complete meiosis only with fertilization.
    • f) The Corpus luteum forms from the now empty secondary follicle. This structure is responsible for the production of higher levels of progesterone.
    • The light microscope image shows the mature secondary follicle.
    • At the centre of the follicle is the oocyte.
    • Note the Zona pellucida which surrounds the oocyte. This surrounds the oocyte and is composed glycoproteins that take part in the acrosome reaction
    Ovary Structure
  • Oogenesis
    • Oogonium (2n) divide by mitosis to produce many oogonia
    • Each oogonia grows within the follicle of cells. Meiosis begins but stops in at prophase I. The oogonia are found within the primary follicles.
    • There are approx 400,000 primary follicles present in the ovary prior to puberty.
    • A Primary Follicles (prophase I) may develop to secondary follicles (metaphase II) under the influence of FSH.
    • Note that the first polar body ( haploid set chromosomes) does not progress beyond metaphase II.
    • The Oocyte does not progress to the end of meiosis unless fertilization takes place.
  • Mammalian Oocyte
    • During follicle development unequal division of the cell during meiosis produces the 1st polar body that can be seen outside the plasma membrane. This will not develop.
    • The Zona pellucida surrounds the structure and is composed of glycoproteins. With the cortical granules they will be involved in the acrosome reaction at fertilization.
    • Around the outside are the follicular cells .
  • Fertilization
  • Fertilization
    • a) The cumulus is a thick loose grouping of cells in a gelatinous matrix. The sperm cell must penetrate this mass to reach the zona pellucida, a glycoprotein matrix surrounding the egg plasma membrane.
    • (b) Contact between the zona pellucida and proteins in the sperm cells membrane trigger a the acrosome reaction.
    • (c) The acrosome vesicle fuses with the sperm plasma membrane and releases enzymes that digest a path through the zona pellucida.
  • Fertilization
    • d) The membrane of the sperm cell and the ovum fuse together. This causes a prominent raising of the egg membrane. At the same time this results in a release of Ca2+ from the endoplasmic reticulum.
    • (e) The cortical vesicle fuse with the plasma membrane releasing enzymes that destroy the sperm binding proteins on the zona pellucida. This prevents polyspermy. The release of Ca2+ also activate meiosis and prepare the cell for completion of reduction division , MII and cell division
  • Human Chorionic Gonadotrophin (HCG)
    • a) The fertilized egg has developed into a blastocyte that will implant into the endometrium
    • b) Implantation of the blastocyst which begins to secrete human chorionic gonadotrophin (hCG)
    • c) hCG passes into the maternal blood. The concentration doubles every 2-3 days and reaches a peak at 8-10 wk's.
    • d) The hCG targets the ovary and the corpus luteum.
    • e) The corpus luteum secretes progesterone and estrogen at high levels .
    • f) The estrogen and progesterone continue to inhibit FSH and LH secretion from the pituitary.
    • g) The progesterone's prevent the breakdown of the endometrium and so the embryo can continue its development into a fetus
  • Human Chorionic Gonadotrophin (HCG)
  • Embryonic Development
    • The fertilized cell divides by mitosis into 2 then 4 then 8 and so on.
    • By day 7 this has formed a hollow ball of cells called the blastocyst.
    • The blastocyst implant into the endometrium and begins to develop towards the early fetal stages
  • Embryonic Development
    • The image represent the stages in the early development of the embryo.
  • Placental membranes
    • This is an ultra sound image of a two month twin pregnancy
  • Placental membranes
    • The image shows the position of the endometrium and two fetus
    • There is amniotic fluid surrounding each fetus to protect and support the fetus
    • The fluid is retained by an amniotic membrane
    • In this example there are two amniotic membranes one for each fetus.
  • Placenta The placenta grows from the embryonic tissue. It attaches to the endometrium of the uterus. Unlike other mammals the human placenta is invades the endometrium very deeply.
  • Placenta
    • a) Umbilical cord attaches the fetus to the placenta
    • b) Umbilical arteries carry deoxygenated blood to the maternal blood to be re-oxygenated. The fetal blood has a much stronger affinity for oxygen than maternal blood
    • c) Umbilical veins carry the oxygenated blood back to the circulatory system of the fetus.
    • d) Placental tissue deep in the endometrial tissue
  • Placenta
    • e) Myometrium
    • f) Endometrium which already has the placenta
    • g)Maternal blood supply
    • h) open ended arterioles forming pools of blood(i)
    • j) Chorionic villi embedded deep in the endometrium and in close association with maternal blood
  • Placenta
    • Exchange a cross the placenta from mother to
    • fetus:
    • Glucose by passive diffusion
    • Amino acids by active transport
    • Lipids by membrane lipid diffusion
    • Oxygen is released by the maternal hemoglobin. The hemoglobin of the fetus has a higher affinity for the oxygen.
    • From Fetus to Mother:
    • carbon dioxide is taken up by the maternal plasma and transported to the lungs of the mother for excretion
    • urea pass's into the maternal blood and passes to her kidneys for excretion
  • Birth and its hormonal control
    • After nine months in the uterus the fetus is fully grown and takes up all the space available.
    • • These cramped conditions push the baby down stretching the lower walls of the uterus. This sends impulses to the mother brain.
    • • The fetus responds to the cramped conditions by producing hormones from the placenta (prostaglandin) which causes myometrial contraction
    • • Progesterone is the hormone of pregnancy and at this stage the high levels of this hormone become less active.
    • All these changes stimulate the secretion of oxytocin from
    • the pituitary and this causes the myometrial contractions of
    • labor
  • Birth
  • Positive feedback :
    • • In this system the stimuli to the brain increases the oxytocin production
    • • In turn the oxytocin stimulate myometrial contraction
    • • Myometrial contraction further stimulates the pituitary of the mother to release more oxytocin
    • • The strength and frequency of the myometrial contractions is further increased.
    • • In turn this further stimulates more oxytocin production
    • • The process builds with stronger and stronger contractions
    • • Final the child passes though the cervix and vagina to be born
    • • Contractions continue for a further period until the placenta is delivered (after birth).
  • Family planning and Contraception
    • (a) Contraceptive pills: a chemical method of contraception. One version uses a combination of progesterone and estrogen that inhibits ovulation. Others are single hormones that require very careful management when taken.     
    • (b) Interuterine device (IUD) placed inside the uterus an exact understanding how this works is unclear. A possible explanation is that it 'irritates' the endometrium such that rejects implantation of embryo's. The device is made from plastic or copper and inserted by a doctor. Nevertheless this device is very effective.
    •   (c) Condom prevents the sperm from reaching the egg. Composed of a thin barrier of latex placed over the penis.
    • (d) The cap,barrier method again made from latex the cap is placed over the cervix to prevent the entry of sperm in semen. It does not a barrier against the transmission of sexual diseases.   
    •   (e) Sterilization is a surgical solution. In men this involves cutting the vas deferens (vasectomy) and prevent sperm entering the semen. In women the surgery cuts or ties the oviducts thus preventing sperm from reaching the egg in fertilization.
    • (f) A behavioral form of contraception is abstinence That is the individual makes the choice to delay sexual intercourse.
  • Ethical Issues of Family planning and contraception
    • The decision on whether to use any method will be determined by an individuals circumstances. Opinions differ on the use of contraceptives and will be affected by a number of different factors including:
            • • Health &Medical
            • • Age
            • • Status
            • • Religion
            • • Legal
  • Amniocentesis Technique that allows the prenatal diagnosis of abnormal development of the fetus.The amniotic fluid is removed with a syringe. It is normal to remove the fluid with the aid of ultrasound imaging that will help reduce the case of striking the fetus or placenta.
    • • Amniotic fluid is removed from the 15th - 18th week
    • • 1ml per week of gestation
    • • Test include karyotyping for Down's Syndrome (mothers 35 have 1/178 chance, 40 have a 1/63 chance, 48 a 1/8 chance)
    • • Test Alpha fetal proteins as a marker for neural tube disorders such as Spina biffida
    • • Complication which cause the spontaneous abortion of the foetus (due to testing) are 1/200 risk
    • • Results take up to 7 days
    • Remember that for any abnormal condition
    • Amniocentesis provides a diagnosis not a cure.
  • Ethical Issues with in vitro fertilization
    • Advantages of IVF: there are as many reasons for this treatment as there are people seeking this treatment. As examples
    • • over comes infertility
    • • allow families for people who must be sterilised e.g.. radiography/chemo therapy cancer patients
    • Disadvantages of IVF:
    • • what happens to unwanted embryo's•what happens to orphaned embryo's
    • • should infertility be by-passed