11.4: Reproduction

1. 11.4: Reproduction

2. 11.4.1

4. spermatids Sertoli cell Developing spermatozoa Germinal epithelium cells (spermatogonium) Leydig cell

8. Each time a spermatogonium divides it may either undergo mitosis, to maintain the number of spermatogonia, or spermatogenesis. Spermatogenesis is the production of spermatids by the process of meiosis. Spermatogenesis begins with meiosis I to produce two haploid cells. Each haploid cell divides again during meiosis II to produce a total of 4 spermatids. Spermatids undergo major rearrangements of their cellular components as they differentiate into sperm. Sertoli cells regulate the process of spermatogenesis and nourish the developing sperm. As the spermatids develop they migrate from the outer edge of the seminiferous tubule to the lumen, the central cavity of the tubule. Once mature, sperm are released into the lumen (at a rate of several million per day) and pushed to the epididymis where they acquire motility.

9. 11.4.3 Spermatogensis: LH (secreted by pituitary gland): Stimulates the secretion of testosterone by the testes FSH (secreted by pituitary gland): Stimulates the first division of meiosis Testosterone (secreted by Leydig cell): Stimulates the second division of meiosis and cells to develop into sperm

11. Primary follicle Germinal epuithelium Secondary oocyte Secondary oocyte Mature follicle

13. Primary follicles Secondary oocyte inside mature follicle

15. Polar bodies

16. Gametogenesis Spermatogenesis Oogenesis

17. Gametogenesis Spermatogenesis Oogenesis Mitosis in germinal epithelium cells (oogonium cells) • Mitosis in germinal epithelium cells (spermatogonium cells)

18. Gametogenesis Spermatogenesis Oogenesis Mitosis in germinal epithelium cells (oogonium cells) • Mitosis in germinal epithelium cells (spermatogonium cells)

19. Gametogenesis Spermatogenesis Oogenesis Mitosis in germinal epithelium cells (oogonium cells) Some cells remain as germinal epithelium cells and some undergo meiosis • Mitosis in germinal epithelium cells (spermatogonium cells) • Some cells remain as germinal epithelium cells and some undergo meiosis

20. Gametogenesis Spermatogenesis Oogenesis Mitosis in germinal epithelium cells (oogonium cells) Some cells remain as germinal epithelium cells and some undergo meiosis Cell growth before meiosis • Mitosis in germinal epithelium cells (spermatogonium cells) • Some cells remain as germinal epithelium cells and some undergo meiosis • Cell growth before meiosis

22. Gametogenesis Spermatogenesis Oogenesis Mitosis in germinal epithelium cells (oogonium cells) Some cells remain as germinal epithelium cells and some undergo meiosis Cell growth before meiosis 2 divisions of meiosis to produce eggs [n] • Mitosis in germinal epithelium cells (spermatogonium cells) • Some cells remain as germinal epithelium cells and some undergo meiosis • Cell growth before meiosis • 2 divisions of meiosis to produce spermatids [n] (not differentiated into spermatozoa yet)

23. Gametogenesis Spermatogenesis Oogenesis Commencing in fetal development , a girl is born with approx 400,000 developing egg cells arrested in Prophase I (meiosis is not continuous) surrounded by a layer of follicle cells forming the primary follicle. • Commences at puberty • Meiosis is continuous

24. Gametogenesis Spermatogenesis Oogenesis Meiosis is not continuous. During puberty, once a month, 6-12 primary follicles develop forming two haploid nuclei [n]. Meiosis is arrested in Prophase II. Now the developing egg cell is called a secondary oocyte. As follicle grows it develops a large fluid filled cavity, now it is called a mature follice. Only one mature follicle develops per month. • Meiosis is continuous

26. Gametogenesis Spermatogenesis Oogenesis One viable egg produced per meiosis and three polar bodies. • Four viable spermatids produced per meiosis

27. Gametogenesis Spermatogenesis Oogenesis One viable egg produced per meiosis and three polar bodies. Unequal division of cytoplasm • Four viable spermatids produced per meiosis • Equal division of cytoplasm

28. Gametogenesis Spermatogenesis Oogenesis One viable egg produced per meiosis and three polar bodies. Unequal division of cytoplasm One egg cell on average every 28 days • Four viable spermatids produced per meiosis • Equal division of cytoplasm • Millions produced daily

29. Gametogenesis Spermatogenesis Oogenesis Released on about day 14 of the menstrual cycle • Released during ejaculation

30. Gametogenesis Spermatogenesis Oogenesis Released on about day 14 of the menstrual cycle • Released during ejaculation

31. Gametogenesis Spermatogenesis Oogenesis Released on about day 14 of the menstrual cycle • Released during ejaculation

32. 11.4.6

34. Corona radiata Zona pellucida nucleus Polar body Cortical granules

35. Polar body in orange

36. 11.4.7

37. 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: *adds fluids that neutralise the vaginal acids

39. 11.4.8

42. 1. Attracted by a chemical signal, sperm swim up the uterus and into the oviduct. 11.4.9

43. 11.4.9 2. Sperm wriggle through corona radiata cells

44. 11.4.9 2. When the first sperm contacts the zona pellucida it triggers the acrosome reaction, in which the contents of the acrosome are released.

45. 11.4.9 3. Proteases from the acrosome digest the zona pellucida enabling the sperm to reach the plasma membrane of the egg.

46. 11.4.9 4. When 1 sperm finally contacts the egg, the cell membranes of egg and sperm fuse, and the sperm head is drawn into the cytoplasm of the egg.

47. 5. As the sperm enters it triggers two changes to the egg. First, it triggers the cortical reaction which causes vesicles near the surface of the egg to harden the zona pellucida thereby preventing additional sperm from entering. 11.4.9 6. Second, it causes the egg to undergo a second meiotic division, producing a haploid gamete and a second polar body.

49. 11.4.10

50. 11.4.10