Sperm Production

1. Sperm Production

2. Male Sex Organs • While the male sex organs are present at birth, they only begin to produce spermatozoa at puberty • For most bulls, this is 7-12 mo.’s of age • At 12-18 mo.’s, sperm production is half that of a fully mature bull.~

5. Pathway of Spermatozoa • Spermatozoa are manufactured in the testes (primary sex organs of the bull) • Spermatozoa are the actual genetic material-carrying cells • Semen/sperm is everything – the cells, the fluids, etc. • Testes have two primary functions • 1. production of spermatozoa • 2. production of male sex hormones • Bulls should have two testes, each with their own compartment inside the scrotum. ~

6. Testes • A testis is made primarily of small tubules (the seminiferous tubules) • Where production of sperm takes place • 0.2 mm in width, up to 4.8 km in length! • As spermatozoa mature, they move toward a duct at the center of each tubule • The testes also produce and secrete fluids that nourish and transport the spermatozoa in route to the epididymus. • This is separate from accessory gland fluids! ~

8. Testes • Leydig cells/interstitial cells are dispersed throughout the testes and produce male hormones (androgens) • Testosterone is considered the primary male hormone • Testosterone is released under the influence of LH from the pituitary gland. • Both LH and FSH are needed for sperm production ~

10. Male Hormones • Male Hormones are necessary for: • Onset and maintenance of sperm production • Sex drive (libido) • Development and maintenance of secondary sex characteristics (organs and features) ~

11. Epididymus • After leaving the testes through ducts in the seminiferous tubules, sperm enter the epididymus. • The epididymus is a tubular structure located on one side of the testes. • It is packed with a milky nutritive substance as well as spermatozoa from the testes. • Spermatozoa mature in the epididymus • An assembly line, not a storage unit!~

13. Vas Deferens • From the epididymus, spermatozoa enter the vas deferens. • This carries the spermatozoa into the body cavity towards the urethra • It is surrounded by muscles that contract during ejaculation. ~

15. Ampullae of Henle, Urethra • The vas deferens enlarges inside the pelvis to form the ampullae • Where spermatozoa are stored and mixed with a nutritive substance. • During copulation, sperm is moved into the urethra. • This is a common pathway for both urine and semen (the mix of the products of the testes and accessory glands.) ~

18. Accessory Glands (3) • There are three accessory glands: • 1. Seminal Vesicles – secrete a fluid high in sugars (fructose) to nourish the spermatozoa – feels like a bag of grapes (palpation) • This fluid also dilutes sperm at ejaculation and serves to activate motility • Rich in proteins, fructose, enzymes. • Secretes prostaglandins, causing uterine contractions • 2. Prostate glands – forms bulk of fluid in semen • Creates a basic pH of 7.5-8 – protects sperm • 3. Cowper’s gland – lubricating substance • Cleanse male and female reproductive tracts prior to passage of spermatozoa (King Sperm’s archers) • These secretions are released almost instantaneously • Male sex hormones are crucial for this process. ~

20. Urethra and Penis • The urethra extends to the tip of the penis, where it exits the body. • Urethra surrounded by smooth muscle – crucial for ejaculation. • Penis is composed of sponge-like blood tissue • Under sexual stimulation, this tissue fills with blood, enlarging it and enabling it to be inserted into a female’s vagina. • Otherwise, it is kept inside the body cavity in most species ~

21. Spermatogenesis Topics: • Blood Testes Barrier • Cryptorchidism • Meiosis • Hormone cycles • Environmental androgens • ~

22. Blood Testis Barrier • Sertoli cells have a “tight junction” barrier which serves to prevent the body from destroying the sperm. • Why would the body destroy sperm? • HINT: Chromosome #’s and types • The BTB is a physical barrier between the testes and the seminiferous tubules. • Think of the grapefruit! ~

24. BTB • The Sertoli cells form a barrier that prevents blood from accessing the lumen of the seminferous tubules. • How is this a good thing? • How is this a bad thing? • What would happen if the BTB were breached? • TPS~

26. BTB Destroyers • Anything that destroys the BTB will lead to an impairment of meiosis and spermatogenesis. • BTB Destroyers include: • Heat • Heavy Metals • Pesticides • Low amounts of FSH and/or Testosterone

27. Case study • You were called to the bull barns of ABS Global in DeForest. • One of their bulls appears to have a fertility problem and your diagnosis is needed. • What things should you check for? • When would the cause of infertility happen if we are just seeing symptoms now? • Would this make a diagnosis more difficult? • TPS~

28. Case Study #2 • Heat damages sperm in 2 main ways: • 1: It can cause a breach in the BTB • 2: DNA polymerase in sperm requires a lower temperature; it will degrade at normal body temp and meiosis will be interrupted. • A stallion has been diagnosed with partial cryptorchidism (kript-or-kai-dizm). • The attending vet has recommended that the animal be put down.~

29. Case Study 2 (Cont) • The breeder is furious with the vet’s suggestion, given this is a prize animal. • She has contacted you for a second opinion. • Will you support the first vet’s suggestion of putting this prize animal down, will you perform an operation, or will you leave the animal alone (given it has one good testis)? • TPS!~

30. Cryptorchidism • Remember the importance of reproduction in agriculture! • Remember the one and only job of a male in the dairy, horse, sheep, etc. industry. • As vets, this is you primary concern in regards to bulls, stallions, and rams. • A testis or both testes can fail to descend for a number of reasons.~

31. Cryptorchidism causes • Cryptorchidism is usually a genetic disorder. • The physiological cause can be hormonal, a hernia, or a malformed structure (e.g. blood vessel that is too short). • As such, animals with the disorder should not be used for breeding purposes. • The risk of infertility in future generations outweighs any benefit an animal could otherwise have.~

32. Other Concerns • Sperm cell formation-discussion to come later • Male health and nutrition • Male-orientation – Diagnosis difficult; can still be viable breeders under the right circumstances

33. Spermatozoa Formation • Spermatozoa cells have to have half of the chromosomes that other cells have • Otherwise the baby would have double the number of chromosomes. • The formation of spermatozoa begins in the testes. • Multiple divisions take place (meiosis) until a final division that reduces the chromosomes to half their original number. ~

34. Spermatogenesis • Spermatogenesis starts at the edge of the seminiferous tubules and moves towards the lumen (center) of each ST. • This begins when a germ cell (reproductive cell) undergoes mitosis, becoming spermatogonia • Spermatogonia: stem cells that create sperm cells • Growth, meiosis, and differentiation follow. ~

38. Steps of Spermatogenesis • Step 1: Mitosis - A germ cell divides into two identical cells, then four - spermatogonia~

39. Mitosis Review • Interphase: nucleus of cell is well defined; nothing much going on otherwise • Prophase: chromosomes form as DNA tightens into coils of chromatin. Chromosomes duplicate. Mitotic spindles form, centrosomes move to opposite sides of cell. ~

40. Mitosis • Prometaphase: nuclear envelope disappears. Microtubules attach to chromosomes and attach to the kinetochore of the chromosome. • Metaphase: chromosomes line up~

41. Mitosis • Anaphase: chromosomes separate, move to opposite ends with microtubules • Telophase: chromosomes begin to dissolve; nuclear envelope re-forms. Cell undergoes cytokinesis~

43. Meiosis • Spermatogonia must then undergo meiosis to reduce their chromosome number to half the normal amount • Meiosis starts the same with a Prophase, Metaphase, Anaphase, and Telophase/Cytokinesis. • However, it then undergoes another round of divisions, this time without duplication. ~

47. Spermatogenesis Animation • http://highered.mcgraw-hill.com/olc/dl/120112/anim0043.swf

48. Hormones and sperm production • After puberty, spermatozoa formation is a continuous process. • This process is controlled by the endocrine system. • FSH and LH are important in stimulating the testes to produce spermatozoa and testosterone. ~

49. Male Hormone Loop • Brain releases GnRH • GnRH tells pituitary to release FSH, LH • LH tells Leydig cells to release testosterone, whichstimulates production of sperm.- note negative feedback! ~

50. Briefly – EDC’s • Endocrine Disrupting Chemicals are a serious concern today. • These chemicals have similar chemical conformations to sex hormones and mimic their effects in the body. • What impact would this have on a body; remember negative feedback! ~