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Chapter 48

Chapter 48. Physiology of Reproduction. Meiosis. Gametes Haploid complement (n) Gametogenesis Process of gamete formation with the reduction by half of the chromosome number Homologous chromosome Carries genes for the same traits. Meiosis. Zygote Fertilized egg Diploid (2n) Meiosis I

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Chapter 48

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  1. Chapter 48 Physiology of Reproduction

  2. Meiosis • Gametes • Haploid complement (n) • Gametogenesis • Process of gamete formation with the reduction by half of the chromosome number • Homologous chromosome • Carries genes for the same traits

  3. Meiosis • Zygote • Fertilized egg • Diploid (2n) • Meiosis I • Prophase • 23 tetrads • Homologues chromosomes synapse • Chiasmata or crossover

  4. Meiosis • Metaphase • Anaphase • Homologues separates • Dyads stays together • Telophase • 2 cells with diploid number of chromosomes

  5. Meiosis • Meiosis II • Prophase • No chromosome replication • Cells are diploid • Metaphase

  6. Meiosis • Anaphase • Breaks of the centromeres will result each cell having one chromatid • 4 daughter cells • Crossover and the way in which the homologues align on the spindle equator during the first maturation division introduces a great variability in the resulting gametes

  7. Spermatogenesis • It is the male gamete formation • Starts at puberty and continues throughout life

  8. Spermatogenesis

  9. Spermatogenesis • Steps of sperm formation: • Spermatogonia (2n) • Stem cell • Found in the seminiferous tubules • It undergoes mitosis and forms one primary spermatocyte and one spermatogonium • Phase regulated by FSH

  10. Spermatogenesis • Primary spermatocyte (2n) • It undergoes to a growth phase • It undergoes to meiosis I after the growth phase and forms the secondary spermatocyte • Secondary spermatocyte (n) • It undergoes meiosis II and produces 4 spermatids

  11. Spermatogenesis • Spermatids (n) • Nonfunctional gametes • No motile • They undergo spermiogenesis and form the sperm

  12. Spermatogenesis • Sperm • Motile • Smaller than the spermatid • Head of the sperm • Contain the genetic material • Acrosome

  13. Spermiogenesis

  14. Spermatogenesis • Midpiece • Centriole that gives rise to the filaments that forms the tail • Mitochondria present • Tail • flagellum

  15. Spermatogenesis • Sertoli cells • Support cells responsible for sperm nourishment

  16. Microscopy of the testes • Seminiferous tubes • Spermatogonia • Pale-staining nuclei • Located at the base of the tubule • Spematocytes • Located in the middle of the tubule wall

  17. Spermatogenesis • Spermatid • Small cell • Round and dark nuclei • Located in the lumen of the tubule • Sperm cell • Seeing under oil immersion • Located in the lumen • Head with acrosome • Midpiece and tail

  18. Spermatogenesis • Interstitial cells • Located between the seminiferous tubules • Testosterone-producing cells

  19. Oogenesis and ovarian cycle • It is the female gamete formation • Steps of the oogenesis: • Before birth • Oogonia • Primitive stem cell • it undergoes mitosis many times • It grows in size and becomes a primary oocyte (arrested in prophase of meiosis I)

  20. Oogenesis and ovarian cycle • Primordial follicles • Capsule formed by a single layer of squamouslike cells that surround the primary oocyte • At birth • Oogonias no longer exists • All cells are oocytes encapsulated by a primordial follicle • No more oocytes will be produced

  21. Oogenesis and ovarian cycle • From birth to puberty • Primary oocytes are quiescent • From puberty and on • Increase of FSH levels cause: • Follicle • One or more primordial follicles to undergo maturation (every 28 days)

  22. Follicle

  23. Oogenesis and ovarian cycle • Formation of primary follicle • From the maturation of the primordial follicle • Follicle cells • The epithelium changes from squamous to simple cuboidal • Many layers of cuboidal cells • Granulosa • It secrets estrogen • It contains the primary oocyte

  24. Oogenesis and ovarian cycle • Secondary follicle • Follicle with several layers of granulosa cells • Presence of antrum • Tertiary follicle (Graafian) • Presence of granulosa cells • Corona radiata

  25. Oogenesis and ovarian cycle • It is a mature follicle that continues secreting increasing amounts of estrogen • It contains the secondary oocyte • It expels the secondary oocyte accompanied by the corona radiata at the middle of the 28-day cycle

  26. Oogenesis and ovarian cycle • Corpus luteum • It comes from the rupture Graafian follicle • It produces mainly progesterone • If pregnancy does not occur it will degenerate and will be replaced by scar tissue

  27. Oogenesis and ovarian cycle • Corpus albicans • Scar tissue resulted from the disintegration of the corpus luteum • Oocyte • Primary oocyte • Meiosis I is completed forming one secondary oocyte and one first polar body

  28. Follicle

  29. Oogenesis

  30. Oogenesis and ovarian cycle • Secondary oocyte • Large cell (contains most of the cytoplasm of the primary oocyte) • Haploid • Arrested in metaphase of meiosis II • It is expelled by the Graafian follicle (ovulation) • It is captured by the uterine tube

  31. Oogenesis and ovarian cycle • If penetrated by the sperm, it will complete meiosis II and will produce a large ovum and one small secondary polar body • Ovum • Chromosomes of the ovum and sperm will combine to form a diploid cell

  32. Oogenesis and ovarian cycle • First polar body • Small cell (almost no cytoplasm) • Produced by the division of the primary oocyte • It will disintegrate • Secondary polar body • Produced by the division of the secondary oocyte • It will also disintegrate

  33. Oogenesis and ovarian cycle • Hormonal cycle • Beginning of the menstrual cycle • FSH is the dominant hormone • Low levels of LH • Low levels of estrogen and progesterone

  34. Oogenesis and ovarian cycle • Before ovulation • Estrogen levels increase • Progesterone level remain low • Ovulation • Caused mainly by a peak of LH • After ovulation • Estrogen levels decrease • Progesterone levels increase • FSH and LH levels decrease

  35. Menstrual cycle • Controlled by ovarian hormones • Menstrual phase • Lasts 1-5 days • Sloughing off of the functional layer of the endometrium with bleeding

  36. Oogenesis and ovarian cycle • Proliferative phase • From day 6-14 • Estrogen is the main hormone • Ovarian follicle grows • Endometrium thickens with proliferation of its glands and blood vessels • Ovulation occur at day 14

  37. Oogenesis and ovarian cycle • Secretory phase • From day 15-28 • Progesterone produced by the corpus luteum is the main hormone • Endometrium thickens even more with further proliferation and coiling of the glands • Uterus is getting ready for the embryo implantation

  38. Oogenesis and ovarian cycle • If no implantation occurs the corpus luteum will deteriorate causing lack of ovarian hormones that will cause deterioration of the functional layer of the endometrium

  39. Menstrual cycle

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