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6.6. & 11.4 Reproduction

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IB Biology 2015

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6.6. & 11.4 Reproduction

  1. 1. 6.6 & 11.4 Reproduction Essential idea: Sexual reproduction involves the development and fusion of haploid gametes.
  2. 2. Understandings Statement Guidance 6.6 U.1 A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone. 6.6 U.2 Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty. 6.6 U.3 Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty 6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones. 11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. 11.4 U.3 Fertilization in animals can be internal or external Fertilization involves the acrosome reaction, fusion of the plasma membrane of the egg and sperm and the cortical reaction. 11.4 U.4 Fertilization involves mechanisms that prevent polyspermy 11.4 U.5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy 11.4 U.6 HCG stimulates the ovary to secrete progesterone during early pregnancy. 11.4 U.7 The placenta facilitates the exchange of materials between the mother and fetus. 11.4 U.8 Estrogen and progesterone are secreted by the placenta once it has formed. 11.4 U.9 Birth is mediated by positive feedback involving estrogen and oxytocin.
  3. 3. Applications and Skills Statement Guidance 6.6 A.1 The use in IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy. 6.6 A.2 William Harvey’s investigation of sexual reproduction in deer 6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions 11.4 A.1 The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis. 11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions.
  4. 4. Male Reproductive System 6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions
  5. 5. Male Reproductive System:Male Reproductive System: 1.1. EpididymusEpididymus:: •Large coiled tube (23 ft. long) that surrounds testes. •Stores sperm (about 20 days). •During ejaculation, about 400 million sperm cells are propelled from epididymis. 6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions
  6. 6. 2.2. Vas Deferens:Vas Deferens: • Long muscular ducts from scrotum to back of bladder. • During ejaculation, the sperm pass from epididymis into these two ducts. *Vasectomy: Each vas deferens is cut to prevent sperm from entering urethra. 3.3. Ejaculatory DuctEjaculatory Duct:: • Short duct after two vas deferens ducts unite. 4.4. UrethraUrethra:: • Deliver sperm to the exterior. • In males, urine and sperm pass through the urethra. 5. Scrotum • maintains temperature (lower than body) that sperm require for normal development
  7. 7. Accessory Glands: Produce semen. Functions of semen: • Activate sperm cells • Provide nutrients for motility • Counteract acidity of vagina and male urethra A. Seminal vesicles (2): Secrete fluid that nourishes sperm. Contribute about 60% of semen volume. B. Prostate gland: Produces a thin milky secretion. • Largest of semen secreting glands. • Contributes 30% of semen volume. C. Bulbourethral glands • Secrete a clear mucus that neutralizes acid from urine in urethra. 6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions
  8. 8. Front View of Male Reproductive SystemFront View of Male Reproductive System
  9. 9. Semen production
  10. 10. 6.6 U.1 A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone. • Initially the development of the embryo is the same in all embryos and embryonic gonads could develop into testis of ovaries. • The developmental pathway for the gonads depends on presence or absence of one gene • When SRY is present the gonads develop into testes. • SRY codes for a DNA binding protein called TDF (testis determining factor). • TDF stimulates the expression of other genes that cause the development of the testis
  11. 11. 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. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  12. 12. 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 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  13. 13. • 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 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  14. 14. 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 (2n) go through Meioses I (n) converting into Secondary Spermatocytes . e) Secondary Spermatocytes go through Meiosis II to produce spermatids (n) *Sertoli cells nourish and allow the spermatids to differentiate to spermatozoa. These are released into the lumen 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  15. 15. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. Spermatogenesis •The male sex cell is designed to deliver just DNA. •The sperm cell contains no cytoplasm and delivers no organelles
  16. 16. Spermatogenesis •It is a process by which spermatogonia are transformed into spermatozoa. It begins at puberty. •At birth: germ cells in the male infant present in the sex cords of the testis are surrounded by supporting cells (Sertoli cells). •At this time the primordial germ cell divides to give spermatogonia. •Spermatogonia gives rise to primary spermatocyte. •1ry spermatocyte by 1st meiotic division gives secondary spermatocyte wg gives haploid spermatids (4 in no.). 11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.
  17. 17. 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. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  18. 18. Spermatogenesis (continued) 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 106 ml-1
  19. 19. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  20. 20. 6.6 U.2 Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty. •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.
  21. 21. Hormonal Control of Spermatogenesis
  22. 22. 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 s • 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. 11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions
  23. 23. Structure of Sperm 11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions
  24. 24. 6.6 U.3 Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty Side View of Female Reproductive System
  25. 25. Major Organs of Female Reproductive System: 1. Ovaries: Produce ova (egg) and sex hormones. »Size and shape of large almond. *Follicles:: A single egg with surrounding cells that nourish and protect it. Women are born with all of their follicles (40,000 to 400,000).
  26. 26. Major Organs of Female Reproductive System: 2. Oviducts (Fallopian Tubes): Transport the egg from the ovary to the uterus. FertilizationFertilization occurs here. 3. Uterus • Has thick walls of smooth muscle responsible for uterine contractions and cramps. • Inner mucous lining, which thickens each month in preparation for pregnancy. If fertilization does not occur, breaks down and is discharged during menstruation. • If fertilization occurs, the egg implants and helps support growth until the placenta develops.
  27. 27. 4. Cervix: Lower portion of the uterus, which projects into the vagina. *Pap smear: Examination of cervical tissue to detect abnormalities. Recommended yearly. *Cervical cancer: Most cases caused by a viral infection. 5. Vagina: Thin walled, muscular chamber. • Receives the sperm and penis • Acid pH kills bacteria and sperm cells • Part of birth canal
  28. 28. Frontal View of Female Reproductive System 6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions
  29. 29. Feedback Regulation of Oogenesis •feedback regulation of female reproductive cycle is negative and positive •leads to female cycles •hypothalamus and pituitary control ovaries •ovarian hormones control uterus 6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.
  30. 30. Two Parts to Female ReproductionTwo Parts to Female Reproduction 1.1. Uterine CycleUterine Cycle • Days 1-5 – Menstruation (“no” steroids) • Days 6-13 - Proliferative phase (Estrogen effect) • Day 14 – Ovulation (LH effect) • Days 15-28 - Secretory phase (Progesterone effect) 2. Ovarian Cycle2. Ovarian Cycle •Follicular Phase - FSH promotes development of an ovarian follicle containing an egg ready to be ovulated secretes increasing levels of estrogen •Luteal Phase –LH promotes ovulation and development of corpus luteum that secretes progesterone 6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.
  31. 31. Ovarian Hormones Regulate Uterine Endometrium • Estrogen stimulates proliferation for implantation of embryo • Progesterone stimulates secretion to nourish embryo until implantation
  32. 32. Female Sex HormoneFemale Sex Hormone Effect on EndometriumEffect on Endometrium • also has effects on breast and other body tissues • PMS: “hormone withdrawal”
  33. 33. Female Cycle
  34. 34. Female Menstrual Cycle /Uterine Cycle : Approximately 28 days. • Menstruation: Days 1-5 of cycle. – Walls of endometrium break down. – Caused by falling levels of progesterone and estrogen. – Can last 3 to 7 days. • Pre-Ovulatory /Proliferative phase (Estrogen effect): Starts around day 6 of cycle. – Rising estrogen levels cause the endometrium to start thickening.
  35. 35. • Ovulation (LH effect) : Occurs around day 14 of cycle. – FSH stimulates growth of ovarian follicle. – LH causes follicle to finish meiosis I (secondary oocyte) and to be released by ovary. – Corpus luteum: Starts to secrete estrogen and progesterone. • Post-ovulatory Secretory phase (Progesterone effect): Starts around day 15. – Endometrium continues to grow in response to rising estrogen and progesterone. – If no fertilization occurs, corpus luteum degenerates and menstruation occurs. – If fertilization occurs, embryo maintains corpus luteum.
  36. 36. 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. 11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.
  37. 37. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.
  38. 38. Ovary structure 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis
  39. 39. 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 1st polar body that will degenerate
  40. 40. 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.
  41. 41. 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 be continues to be part of the follicle. • Zona pellucida surrounds the structure and is composed of glycoproteins. • Cortical granules involved in the acrosome reaction at fertilization. • Follicular cells found round the outside are the follicle. 11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions
  42. 42. 11.4 U.3 Fertilization in animals can be internal or external • Sexual Reproduction – Frogs External fertilization
  43. 43. Fertilization = sperm + egg External Fertilization • Egg shed by female, fert. by male in water • Environmental cues / courtship behavior • Large # gametes  low survival • Eg. fish, amphibians Internal Fertilization • Sperm deposited in female reprod. tract • Cooperative behavior • Dry environment • Fewer gametes, fewer zygotes  greater survival External Devel. •Tough eggshell •Eg. reptiles, birds, platypus Internal Devel. •High parental care •Eg. placentals, sharks, some reptiles 11.4 U.3 Fertilization in animals can be internal or external
  44. 44. Fertilization 11.4 U.4 Fertilization involves mechanisms that prevent polyspermy
  45. 45. 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. 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
  46. 46. 6.6 A.2 William Harvey’s investigation of sexual reproduction in deer • Embryogenesis an early theory of egg development proposed by Aristotle. His idea called the Seed and soil theory, believed that males produce seed, females form an egg which mixes with menstrual blood to develop into a fetus inside the mother • William Harvey tested this idea by shooting deer during mating season • He discovered that it took months for the fertilized egg to develop in the uterus. • This help debunk the idea of Spontaneous generation and lead to a better understanding of embryology. (1578-1657)
  47. 47. Human embryonic development •Conception: in oviduct •Implantation: in uterus •Hormones: – Human Chorionic Gonadotropin (hCG): maintain estrogens in early pregnancy; pregnancy test •Human gestation (pregnancy) = 40 weeks •Egg lodged in oviduct = ectopic (tubal) pregnancy 11.4 U.5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy .
  48. 48. Zygote the fused sperm and egg cell. This cell undergoes rapid mitotic cell division, but these do not increase the size of the zygote Morula Cleavage produces a solid sphere of cells, still surrounded by zona pellucida. Blastocyst At 4.5 to 5 days, cells have developed into a hollow ball of cells. At this stage the cell enters the uterus.
  49. 49. From ovulation to implantation Cleavage starts Fertilization occurs Uterus Ovulation Ovary Endometrium The blastocyst implants Cleavage continues Formation of Zygote
  50. 50. Implantation of blastocyst Blastocyst Endo- metrium Cavity Inner cell mass Trophoblast Early Postfertilization Events
  51. 51. 11.4 U.6 HCG stimulates the ovary to secrete progesterone during early pregnancy. 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
  52. 52. Human Chorionic Gonadotrophin (HCG)
  53. 53. 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.
  54. 54. Functions of the placenta: 1. Transfer gases 2. Transport nutrients 3. Excretion of wastes 4. Hormone production – temporary endocrine organ – estrogen and progesterone 5. Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross 11.4 U.7 The placenta facilitates the exchange of materials between the mother and fetus.
  55. 55. 11.4 U.8 Estrogen and progesterone are secreted by the placenta once it has formed. As the placenta forms and grows, it develops the ability to produce hormones. Between weeks 6-9 of pregnancy, the placenta takes over from the ovaries as the main producer of progesterone and estrogen, vital to the establishment of pregnancy. Progesterone also has many functions during mid to late pregnancy, including: • Preventing the muscles of the womb contracting until the onset of labor • Preventing lactation until after pregnancy • Strengthening the muscles of the pelvic wall in preparation for labor Estrogen the placenta produces several distinct estrogens • Stimulate growth of the myometrium and oxytocin receptors, thereby preparing the uterus for parturition. • Stimulate mammary gland development.
  56. 56. 11.4 U.9 Birth is mediated by positive feedback involving estrogen and oxytocin. Estrogen
  57. 57. 6.6 A.1 The use in IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy.
  58. 58. 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 sterilized 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
  59. 59. 11.4 A.1 The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals. • Altricial "requiring nourishment“, refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born • Precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. These are usually have large body masses. Correlation between maximum lifespan (tmax) and typical adult body mass (M) using all species (n = 1,701)

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