The Reproductive System

1. The Reproductive System George Liapakis, PhD

2. Reproduction depends on the union of male and female reproductive (or germ) cells • Germ cells are called gametes. Gametes Spermatozoa(or sperm) in males Ova (or eggs) in females

3. GAMETOGENESIS • Gametogenesis: The production of gametes in reproductive organs (spermatogenesis, oogenesis) • Gonads: reproductive organs, in which gametogenesis takes place. • The gonads in both sexes secrete sex hormones, which are steroids.

4. Gonads Females Ovaries They produce eggs (or ova) They produce and secrete the sex hormones estrogen and progesterone Males Testes They produce sperm They produce and secrete the sex hormone testosterone

5. Reproductive system in both males and females 1 Gonads Reproductive tract A system of ducts, which serve to transport or house the gametes after their production. 2 Accessory sex glands They empty their secretions into the reproductive tract. 3

6. Puberty • It begins sometime between the ages of 10 and 14 • It lasts 3 to 5 years • Arousal and maturation of a previously immature and nonfunctional reproductive system in males and females. • Secretion of sex hormones

7. The Reproductive System of the Male George Liapakis, PhD

8. Testes • They are located in a skin-covered sac which is called scrotum. • Testes are located outside the abdominal cavity

9. Testes • Testes need to be in a cooler environment than the rest of our body. • Spermatogenesis is temperature sensitive and cannot occur at normal body temperature (2°C below body temperature). • Scrotal muscles are under the control of atemperature-sensitive spinal reflex mechanism

10. Location of testes before and after birth • Testes exit the abdominal cavity at the end of the fetal life. • The descent of testes from the abdomen into the scrotum is induced by testosterone. • After birth testosterone secretion ceases. The remainder of the reproductive system remains immature and nonfunctional until puberty • Cryptorchidism • Undescended testes, which cannot produce viable sperm

11. The testes during puberty • The testes start secreting testosterone again • Under the influence of testosterone the testes enlarge and produce sperm (spermatogenesis) for the first time • Under the influence of testosterone the accessory sex glands enlarge and become secretory • After puberty testosterone production and spermatogenesis occur continuously throughout the male’s life.

12. More effects of testosterone • It helps maintain the sex drive in the adult male. • It gives male characteristics, such as beard and chest hair, a deep voice, thick skin • It shapes the male body by promoting muscle growth.

13. Spermatogenesis • Production of sperm (or spermatozoa) from spermatogonia • Spermatogonia : Relatively undifferentiated, initial or primary germ cells • Spermatozoa: Highly differentiated, extremely specialized, mobile cells • Spermatogenesis encompasses three major stages: mitotic proliferation, meiosis, and packaging

14. Mitotic proliferation Mitotic division of a spermatogoniumresults in the creation of two daughter cells. One of the daughter cells remains as an undifferentiated spermatogonium, thus maintaining the germ-cell line The other daughter cell divides (2 mitotic divisions) to finally give four identical cells, which are called primary spermatocytes.

15. Meiosis Theprimary spermatocytes through a meiotic division give the secondary spermatocytes. Thesecondaryspermatocytesthrough a meiotic division yield the spermatids

16. Spermiogenesis The spermatids do not further divide but rather are remodeled into spermatozoa (spermiogenesis). Spermiogenesis: Packaging of the cell elements of spermatids,which aims to produce from spermatids extremely specialized, mobile spermatozoa that are able to accomplish fertilization.

17. Where does spermatogenesis take place? • Germ cells are located within specific tubules, the seminiferous tubules of testes • Mitotic and meiotic divisions, as well as packaging of spermatogenesis take place within the seminiferous tubules.

18. The seminiferous tubules Outermost layer of the tubule

19. Spermatogenesis Spermatogonia are located in the outermost layer of the tubule After a mitotic division a spermatogoniumgives two daughter cells One daughter cell remains at the outer edge of the tubule as an undifferentiated spermatogonium, thus keeping stable the number of spermatogonia. The other daughter cell starts moving toward the lumen while undergoing the various steps required to form sperm

20. Spermatogenesis During spermatogenesis, developing sperm cells arising from spermatogonia migrate toward the lumen of the seminiferous tubule, undergoing their further divisions during this migration

21. Spermatogenesis The highly differentiated extremely specialized, mobile spermatozoa are in the lumen, with the various stages of sperm development between the lumen and the outermost layer of the tubule

22. Supportive role of Sertoli cells in spermatogenesis Sertoli cells are located within the seminiferous tubules of testes Each Sertoli cell spans the entire distance from the outer surface of the seminiferous tubule to the lumen The sperm cells migrate in close association with adjacent epithelial cells, which are called Sertoli cells and provide crucial support for spermatogenesis. Lumen of the tubule Outermost layer of the tubule

23. Supportive role of Sertoli cells in spermatogenesis The Sertoli cells envelop the migrating sperm cells, which remain buried throughout their development. Sertoli cells protect the sperm cells from various sperm cell harmful substances in the blood. Sertoli cells nourish the sperm cells and destroy (phagocytosis) the defective ones.

24. Hormonal control of Spermatogenesis In Spermatogenesis two hormones play an important role: Testosterone Follicle-stimulating hormone (FSH).   FSHis needed for spermatid remodeling. Testosteroneis essential for the division of germ cells Both exert their effects on spermatogenesis by acting on Sertoli cells

25. Secretion of testosterone • Testosterone is produced and secreted by the Leydig, or interstitial, cells. • Leydig cellsare located in the connective tissue between the seminiferous tubules, which is called the interstitial tissue. • Some of the testosterone is secreted into the blood and acts on target cells, whereas the largest portion goes into the seminiferous tubules, where it plays an important role in sperm production.

26. Secretion of testosterone • The secretion of testosterone is under the control of the luteinizing hormone (LH), which is secreted from the anterior pituitary. LHacts on the Leydig cells. • LH secretion is stimulated by the hypothalamic gonadotropin-releasing hormone (GnRH) Testosterone exerts its effects on spermatogenesis by acting on Sertoli cells

27. Follicle-stimulating hormone (FSH) • FSH is secreted from the anterior pituitary. • FSH secretion is stimulated by GnRH. FSH exerts its effects on spermatogenesis by acting on Sertoli cells

28. Both testosterone and FSH exert their effects on spermatogenesis by acting on Sertoli cells

29. Negative-feedback loops Testosterone inhibits directly the secretion of LH by acting on the anterior pituitary Testosterone inhibits indirectly the secretion of both FSH and LH, by acting on hypothalamus, where it inhibits the secretion of GnRH. Inhibin is secreted by Sertoli cells and inhibits only FSH secretion by directly acting on the anterior pituitary.

30. Hormonal secretion and Puberty • After birth the testes become dormant until puberty. During this period, LH and FSH are not secreted at adequate levels to stimulate any significant activity in testes and GnRHactivity is inhibited • Secretion of high levels of GnRH, LH and FSH starts at puberty.

31. What is the fate of sperm after its production?

32. As they leave the testis, sperm cells are not capable of either moving or fertilizing. • Specific secretions from the accessory sex glands, are important to the viability and motility of the sperm. • These glands include the seminal vesicles and the prostate • The seminal glands supply the sperm cells with nutrients and the prostate gland secretes a fluid that contributes to the viability of sperm into the vagina.

33. SUMMARY Introduction of the reproductive system in both males and females: gonads (ovaries, testes), reproductive tract and accessory sex glands Gametes (ova, sperm) Gametogenesis (spermatogenesis, oogenesis) The gonads in both sexes secrete sex hormones (estrogen and progesterone in females, testosterone in males) Puberty

34. SUMMARY Location of testes-Scrotum Spermatogenesis is temperature sensitive Descent of testes from the abdomen before birth. Role of testosterone Cryptorchidism The reproductive system remains immature and nonfunctional after birth until puberty The testes during puberty Spermatogenesis: Production of spermatozoa from spermatogonia, through mitotic divisions, meiosis and packaging (spermiogenesis)

35. SUMMARY Location of spermatogenesis Supportive role of Sertoli cells in spermatogenesis Hormonal control of Spermatogenesis Negative-feedback loops Hormonal secretion and puberty The accessory sex glands, are important to the viability and motility of the sperm

36. NEXT LECTURE The Reproductive System