Spermatogenesis
Spermatogenesis is the process by which the testes produce mature spermatozoa. It takes place inside the seminiferous tubules and continues from puberty until death. The whole cycle takes about 72 days in humans.
Hormonal Control
- FSH
- Released from the anterior pituitary
- Stimulates spermatogenesis in the seminiferous tubules
- Works by enhancing the action of testosterone on Sertoli cells
- LH
- Released from the anterior pituitary
- Stimulates testosterone production in the interstitial (Leydig) cells
- Testosterone
- Produced by Leydig cells
- Directly stimulates spermatogenesis and supports maturation of sperm
Stages of Spermatogenesis
1. Spermatogonia (Diploid, 2N)
- These are the primordial germ cells found along the basal membrane of the seminiferous tubules
- Undergo mitosis throughout life to maintain the stem-cell pool
- Some differentiate → primary spermatocytes
2. Primary Spermatocytes (Diploid, 2N)
- Enter Meiosis I
- Move slightly toward the lumen
3. Secondary Spermatocytes (Haploid, N)
- Formed after completion of Meiosis I
- Quickly enter Meiosis II
4. Spermatids (Haploid, N)
- Formed after Meiosis II
- Non-motile, immature, round cells
- Located near the lumen
5. Spermiogenesis (not a division — a transformation)
- Spermatids modify their shape and structure to become mature spermatozoa
- Key changes:
- Condensation of nucleus
- Formation of acrosome
- Development of flagellum
- Loss of excess cytoplasm
6. Mature Spermatozoa
- Released into the lumen of the seminiferous tubule
- Fully haploid and motile
Characteristics of Male Gametes (Sperm)
- Haploid cells that carry either X or Y chromosome (1:1 ratio)
- Head contains the nucleus + acrosome
- Midpiece filled with mitochondria
- Tail gives motility for reaching the egg
- Millions are produced per day
- Normal fertility requires 20–50 million sperm/mL of semen