Lecture Notes: Sexual Differentiation, Sex Determination, and Gametogenesis

5.1. Spermatogenesis

5.1 Location and Timeline

• Occurs within seminiferous tubules of testes.
• Supported by Sertoli cells (“nurse cells”).
• Entire cycle takes ~74 days.
• Continuous from puberty throughout life.

5.2 Phases of Spermatogenesis

1.  Spermatocytogenesis:

a.     Mitotic proliferation of spermatogonia (diploid stem cells) → primary spermatocytes.

§  Type A → stem cells

§  Type B → commit to meiosis

b.    Meiosis I: primary spermatocytes → secondary spermatocytes.

c.     Meiosis II: secondary spermatocytes → spermatids.

2.    Spermiogenesis:

a.     Spermatids transform into mature spermatozoa

b.    Formation of acrosome, flagellum, nuclear condensation.

3. Spermiation

1. 1. Release of mature sperm into lumen.

5.3 Hormonal Regulation

• GnRH (from hypothalamus) → stimulates anterior pituitary to release:
  • FSH → stimulates Sertoli cells
  • LH → stimulates Leydig cells to produce testosterone
• Testosterone + FSH → essential for completion of spermatogenesis
• Inhibin B from Sertoli cells → negative feedback to pituitary