Gametogenesis – Production of sperm & eggs

1. Gametogenesis – Production of sperm & eggs

2. IB Assessment Statement • Draw and label a diagram of a mature sperm and egg.

3. Structure of Sperm Remember this is a single cell ~50 um long and 3 um wide at the 'head'. The 40 um tail is omitted from this diagram. The acrosome vesicle contains the enzymes required to digest its way though the ovum wall.

4. Structure of Sperm 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 fibres add longitudinal rigidity and provide a mechanism of propulsion.

5. Structure of mature secondary oocyte The haploid nuclei (arrested at prophase II ) sits inside a cell with a large volume of cytoplasm (yolk). 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 fertilisation. Around the outside are the follicular cells.

8. Gametogenesis Introduction • Gametogenesis is the formation of gametes (sperm and egg cells) • The process of gametogenesis is based on meiosis, but differs in females and males • Oogenesis is development of mature ova (egg) • Spermatogenesis is production of mature sperm

9. Gametogenesis Sequence • Multiplication phase – gamete cells reproduce by mitosis. The stage is repeated many times • Growth phase – gamete cells called primary spermatocytes grow and mature • Maturation phase -- Cells undergo meiosis and form haploid cells.

10. Gametogenesis Sequence – Maturation Maturation phase -- Cells undergo meiosis and form haploid cells. • The products of meiosis I are secondary spermocytes and secondary oocytes. • Spermocytes are haploid cells formed in the seminiferous tubules of testes; that will develop in to sperm. • Secondary oocytes are haploid cells derived from a primary oocyte shortly before ovulation in the ovary • The products of meiosis II are spermatids(sperm) and ova (egg)

11. The Structure and Function of the Testis • Spermatogenesis begins at puberty and continues throughout life. • It is the production of sperm.

12. IB Assessment Statement • Annotate a light micrograph of testis tissue to show the location and function of interstitial cell (leydig cells), germinal epithelium cells, developing spermatozoa, and Sertoli cells

18. Seminiferous Tubule of the Testis • Spermazoas • Spermatids • Secondary spermatocytes • Primary spermatocytes

19. IB Assessment statement • Outline the role of the epididymis seminal vesicle and prostate gland in the production of semen. spermatogenesis, including the number of gametes and the timing of the formation and release of gametes.

20. IB Learning Objective • Outline the role of the epididymis seminal vesicle and prostate gland in the production of semen 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 and minerals ions mineral ions

21. Outline the processes involved in spermatogenesis within the testis, including mitosis, cell growth, the two divisions of meiosis and cell differentiation

22. The Structure and Function of the Testis • Testis consists of many seminferous tubules. • These tubules are lined with germinal epithelial cells which divide repeatedly

23. Seminferous tubules. • These tubules are also lined with nutritive cells (Sertoli Cells) • Sertoli cells feed sperm producing cells (spermatocytes, secondary spermatocytes and spermatids) in the seminferous tubules.

25. The Structure and Function of the Testis • Between theses seminferous tubules is connective tissues that contain blood capillaries, with groups of interstitial cells • These interstitial cells are hormone-secreting (endocrine gland)

27. The Structure and Function of the Testis • These semminiferous tubules in the testes the sperm drains into the epididymis. • The epididymis is a very coiled tube that leads to the sperm duct

28. Sequence of Mature Sperm Production • Germinal epithelial cells of the seminiferous tubule undergo mitotic division and produce many diploid cells called primaryspermatocytes. • Primary spermatocytes undergo meiosis I and form haploid secondary spermatocytes.

29. Sequence of Mature Sperm Production • These haploid secondary spermatocytes undergo meiosis II and form spermatids • These spermatids are supported by the serotoli cells • Spermatids become mature sperm called spermatozoa.

30. From spermatid to spermazoan (mature sperm)

31. Sequence of Mature Sperm Production • Spermatids move from the seminferous tubules into the epididymis. • In the Epididymis, spermatids mature and become motile spermazoans • The epididymis is a place where sperm is stored and where it completes it growth and development

33. These epididymis tubules drain into a system of channel which leads to the sperm ducts. • It takes 20 days for the sperm to pass through these complicated epididymis tubules

34. During these 20 days they develop into motile strong cell with the ability to fertilize any egg. • During ejaculation the sperm are propelled from the epididymis through the muscular vas deferens ( a tube that goes from the epididymis to the urethra).

35. Sperm are transported in a nutritive fluid secreted by glands, mainly the seminal vesicles and prostate gland. • Semen is highly basic (alkaline) solution.

37. From spermatid to spermazoan (mature sperm)

39. LE 46-12 Epididymis Seminiferous tubule Testis Cross section of seminiferous tubule Spermatogonium Sertoli cell nucleus Mitotic division, producing large numbers of spermatogonia Differentiation and onset of meiosis I Primary spermatocyte (in prophase of meiosis I) Meiosis I completed Secondary spermatocyte Meiosis II Lumen of Seminiferous tubule Early spermatids Spermatids (at two stages of differentiation) Differentiation Neck Sperm cells Tail Midpiece Head Plasma membrane Acrosome Nucleus Mitochondria

40. Spermogenesis

41. Spermarozoa

42. IB Learning Objective • State the role of LH, testosterone and FSH in spermatogenesis.

43. Roles of Hormones in Spermatogenesis • Puberty is triggered by the hypothalamus part of the brain. • Hypothalamus stimulates the pituitary gland to produce and release FSH hormones and LH hormones. • FSH (follicle-stimulating hormone) initiates sperm production • LH (luteinising hormone) stimulates the endocrine cells of the testes to release progesterone.

44. LE 46-14 Stimuli from other areas in the brain Hypothalamus Anterior pituitary Negative feedback FSH LH Leydig cells make testosterone Primary and secondary sex characteristics Sertoli cells Testis Spermatogenesis

45. Roles of Hormones in Spermatogenesis • Activity of testosterone is regulated by a negative feedback system. • High testosterone levels suppress LH hormones stimulation. • Low LH in blood reduce the release of testosterone.

48. Animation on Spermatogenesis • http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter28/animation__spermatogenesis__quiz_1_.html • http://wps.aw.com/bc_martini_eap_4/40/10469/2680298.cw/content/index.html

49. IB LEARNING OBJECTIVE • Annotate a diagram of the ovary to show the location and function of germinal epithelium, primary follicles, mature follicle and secondary oocyte.