Spermatogenesis

Question 1

Testicular anatomy

Answer 1

• Spermatogenesis occurs in seminiferous tubules
• Rete testis receives drainage from seminiferous tubules
• Rete testis empties into epididymis
• Epididymis function is to store sperm, help sperm mature, has 3 regions
  
  • Head: concentration
  • Body: maturation
  • Tail: storage
• Spermatogenesis occurs from basement membrane inward to seminiferous tubule lumen
• Blood-testis barrier formed by tight junctions between Sertoli cells
  
  • Physical barrier between blood vessels and seminiferous tubules
  • Prevents some proteins and toxic agents from entering seminiferous tubules
  • Differentiating germ cells (with 1N haploid DNA) are potentially antigenic/recognizable as foreign - barrier sequesters these cells from the blood environment

Question 2

Spermatogenesis and spermiogenesis

Answer 2

• Spermatogenesis occurs in a cyclical fashion that is continuous: at any given time or place in the seminiferous vesicle, different stages of spermatogenesis will be seen (about 60 different stages in humans)
• Defined as 3 stage process by which spermatogonial stem cells give rise to spermatozoon:
  
  • Proliferative phase: spermatogonia mitotically divide = 1 primary spermatocyte + 1 copy of self
  • Meiotic phase: spermatocytes undergo meiosis that reduce the chromosome number by half
  • Spermiogenic phase / spermiogenesis: haploid spermatid differentiated into mature spermatozoa

Question 3

Spermiogenesis

Answer 3

• Haploid spermatid differentiated into mature spermatozoa
  
  • Golgi phase = G apparatus produces acrosomal vesicles - most prominent cytoplasmic inclusion
  • Cap phase = acrosomal vesicle migrate to one end of spermatid, capping sperm
  • Acrosomal phase
  • Maturational phase
• Spermiation is final step of spermatogenesis in Sertoli cell, in which sperm is released from Sertoli cell into the epididymis (via rete testis)

Question 4

Functions of Leydig (interstitial) cells

Answer 4

• Produce androgens including 95% of testosterone; stimulated to do so by LH
• T synergizes with FSH to stimulate formation of ABP in Sertoli cells
• Synthesis of StAR, SCP, SAP
  
  • Help cholesterol get into cell and make steroids
• Required for spermiogenesis
• Have LH receptors (Gs)

Question 5

Functions of Sertoli (supporting) cells

Answer 5

• Form blood testis barrier via tight juntions
• Produce ABP - dramatically increase effectiveness of testosterone
• Nurture gametes (47 spermatozoa per Sertoli cell)
• Have FSH receptors (Gs)
  
  • Produces estrogens from T via aromatase
  • Produces inhibin and other growth factors
• Support Leydig cells with other growth factors + inhibin

Question 6

Hormonal control of spermatogenesis

Answer 6

• Spermatogenesis stimulated by testosterone, under control of HPT axis