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Animal Science 434

Animal Science 434. Lecture 12: Spermatogenesis. Production of Fertile Sperm. hormonal regulation of the testis mitotic division of spermatogonia meiotic divisions of spermatocytes morphologic transformation of spermatids into spermatozoa. Hormonal Regulation of the Testis. LH. LH. LH.

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Animal Science 434

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  1. Animal Science 434 Lecture 12: Spermatogenesis

  2. Production of Fertile Sperm • hormonal regulation of the testis • mitotic division of spermatogonia • meiotic divisions of spermatocytes • morphologic transformation of spermatids into spermatozoa

  3. Hormonal Regulation of the Testis

  4. LH LH LH LH GnRH GnRH GnRH GnRH FSH FSH FSH FSH

  5. Time of Day (24 hr) Pulses are important !

  6. FSH on Sertoli Cells • estradiol • inhibin • ABP • tight junctions Negative Feedback of Estradiol and Inhibin To Epid. Negative Feedback of Androgens FSH LH ABP + T E2 Inhibin T TJ ABP Hypothalamus GnRH Ant. Pituitary Leydig Cells Sertoli Cells Germ Cells Seminiferous Tubule

  7. Spermatogenesis

  8. Sertoli Cell Myoid Cells

  9. Sertoli Cell

  10. Every 13.5 Days sperm are released from this point Spermatozoa Round Spermatid Secondary Spermatocyte Primary Spermatocyte Every 13.5 Days a new group of cells initiate the cycle Spermatogonia

  11. Typical Sequence of Spermatogenesis A Spermatogonia (A, intermediate, B) A A Spermato-cytogenesis I I B B Primary Spermatocyte Mitosis P P Meiosis S S SecondarySpermatocyte RS RS Round Spermatid Spermio-genesis Spermatozoa SP SP Spermiation Rete Testis

  12. Many Sperm are Produced Potential Sperm Produced 1 A 2 A A 4 I I 8 B B 16 P P 32 S S 64 RS RS SP SP

  13. Mitotic Divisions • species dependent • between 2 and 6 divisions (4 to 64 potential daughter cells produced) • classifications vary among species and investigators • A1, A2, A3, A4, B 1, B2, P • Ad, Ap, B, P • As, A0, A1,A2, I, B, P • cytoplasmic bridges form between daughter cells

  14. Degenerating Spermatogonia (Apoptosis, as high as 75%) Cytoplasmic Bridges Present Among Daughter Cells All develop surrounded by 1 Sertoli cell !

  15. Germ Cells / Sertoli Cell Species Primary Round Max. Potential Spermatocytes Spermatids Spermatids Equine 3.0 ± 0.2 10.9 ± 0.9 64 Bovine 1.2 ± 0.1 5.2 ± 0.6 64 Human 1.3 ± 0.1 4.2 ± 0.2 16

  16. Apoptosis of Germ Cells • Season • Disease • Trauma or heat • Hormone levels • Normal part of spermatogenesis

  17. Stem Cell Renewal • To keep spermatogenesis going indefinitely • Replenish testis incase of injury, trauma, or high heat

  18. FSH Periodic Entry of Cells into Mitosis A2 Spermatogonial Renewal in the Rat and Bull A1 Stem Cell Pool A3 A4 In B P

  19. FSH Ap Spermatogonial Renewal in the Primate Ad Stem Cell Pool B P

  20. Stem Cell

  21. Spermiogenesis

  22. Golgi Phase Development of Acrosome Migration of Centrioles

  23. Cap Phase Acrosome Development Continues Flagellum Elongates

  24. Acrosomal Phase Acrosome Manchette Elongation

  25. Maturation Phase Manchette disapears Mitochondria migrate Dense fibers form

  26. Spermiation

  27. Spermiation

  28. Temporal Relationships of Spermatogenesis

  29. Spermatogenesis 57 days Stallion

  30. Multiple Generations of Germ Cells

  31. Bull Spermatogenesis

  32. Stages • Specific cellular associations within a small segment of a seminiferous tubule • stages are not the same length in time

  33. Bull Spermatogenesis - Stages

  34. Stages • Specific cellular associations within a small segment of a seminiferous tubule • stages are not the same length in time

  35. Bull Spermatogenesis - Stages

  36. Cycle • progression through sequence of all stages

  37. Bull Spermatogenesis - Cycles

  38. Cycle • progression through sequence of all stages • 4.5 cycles to form spermatozoa • some species variation

  39. Bull Ram Boar Stallion Man cycle (days) 13.5 10.4 8.3 12.2 16 Spermatogenesis61 47 39 57 75 Duration of Spermatogenesis

  40. Coordination of Stages Form Waves • some portion of seminiferous tubule is always releasing sperm

  41. Compartmentalization of Spermatogenesisand theBlood Testis Barrier

  42. Seminiferous Tubule andInterstitial Tissue

  43. Blood Vessel Interstitial Tissue • Vascular System Provides • Nutrients • Oxygen • Growth Factors • Hormones

  44. Blood Vessel

  45. Compartments Myoid Cells Tight Junctions Luminal Adluminal Basal

  46. Cycles and Stages

  47. Compartmentalization • Basal • mitosis • spermatogonia (A, I, B) • primary spermatocytes • Adluminal • meiosis • primary spermatocytes • secondary spermatocytes • spermatids • spermiogenesis • Lumen • spermiation

  48. !!!!! Blood Testis Barrier • Sertoli cells and associated tight junctions • first appears at puberty • induced by FSH • after puberty can be maintained by FSH and/or testosterone • essential for meiosis

  49. Tight Junction Role in Meiosis • Sertoli cells can manipulate environment around 1° spermatocyte • Enters meiosis • Completes meiosis • Destruction of TJ causes impairment of meiosis • Heat, heavy metals, pesticides, lack of FSH or Testosterone

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