1. Lecture 12: Spermatogenesis
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. Negative Feedback of Androgens
FSH on Sertoli Cells
estradiol
inhibin
ABP
tight junctions
Hypothalamus
Negative Feedback of Androgens
GnRH
Negative Feedback of
Estradiol and Inhibin
Ant.
Pituitary LH
FSH
ABP + T To
Epid. E2
Inhibin
Leydig
Cells
Sertoli
Cells T
ABP TJ
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. Secondary Spermatocyte
Typical Sequence of Spermatogenesis A
Spermatogonia
(A, intermediate, B) A A
Spermato- cytogenesis I I
Primary
Spermatocyte B B
Mitosis P P
Meiosis
Secondary Spermatocyte S S RS RS
Round Spermatid
Spermio- genesis
Spermatozoa SP SP
Spermiation
Rete Testis

12. Many Sperm are Produced
Potential Sperm Produced 1 A A A 2 4 I I 8 B B 16 P P S S 32 RS RS 64 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. All develop surrounded by 1 Sertoli cell !
Cytoplasmic Bridges Present Among Daughter Cells
All develop surrounded by 1 Sertoli cell !
Degenerating Spermatogonia (Apoptosis, as high as 75%)

15. Germ Cells / Sertoli Cell
Species Primary Round Max. Potential Spermatocytes Spermatids Spermatids
Equine 3.0 ± ±
Bovine 1.2 ± ±
Human 1.3 ± ±

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

19. Spermatogonial Renewal in the PrimateAp
Spermatogonial
Renewal in the
Primate Ad
Stem Cell
Pool
FSH 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. Bull Spermatogenesis

30. Stallion Spermatogenesis

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. Stages

34. Stages

35. Stages

36. Stages

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

38. Cycles and Stages
57 days
Stallion

39. Cycles and Stages

40. Cycles and Stages

41. Cycles and Stages

42. Cycles and Stages

43. Cycle
progression through sequence of all stages

44. Cycles and Stages
57 days
(12.2 days/cycle) * (4.7 cycles) = 57 days

45. Duration of Spermatogenesis
Bull Ram Boar Stallion Man
cycle (days)
Spermatogenesis

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

47. Compartmentalization of Spermatogenesis and the Blood Testis Barrier

48. Seminiferous Tubule and Interstitial Tissue

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

50. Blood Vessel

51. Compartments
Tight Junctions
Myoid Cells
Luminal
Adluminal
Basal

52. Cycles and Stages

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

54. 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

55. Compartments
Tight Junctions
Myoid Cells
Luminal
Adluminal
Basal

56. Capacity for Sperm Production
Species Testis Sperm/gm DSP Weight (gm) (X 106) (X 109)
Dairy Bull
Beef Bull
Ram
Boar
Stallion
Man

57. Duration of Spermatogenesis
Bull Ram Boar Stallion Man
cycle (days)
Spermatogenesis

58. Spermatogonial Renewal in the PrimateAp
Spermatogonial
Renewal in the
Primate Ad
Stem Cell
Pool
FSH B P

59. Capacity for Sperm Production
Species Testis Sperm/gm DSP Weight (gm) (X 106) (X 109)
Dairy Bull
Beef Bull
Ram
Boar
Stallion
Man

60. Variation in Sperm Production
Testis Size
Efficiency of spermatogenesis
mitotic division
degeneration of germ cells
Length of spermatogenesis

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

62. Over Population of Spermatogonia
Tight Junction
Sertoli
Sertoli SG SG SG SG SG SG SG SG SG
Basement Membrane
Normal
Apoptosis Inhibited PS SG
Basement Membrane
Sertoli AP SG
Basement Membrane
Sertoli

63. Animation of Spermatogenesis