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 TJ
Sertoli
Cells T
ABP
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