Reproductive hormones in males

Spermatogenesis is controlled by FSH, LH, and testosterone:

• FSH enters the testes and stimulates the Sertoli cells to begin facilitating spermatogenesis using negative feedback, as illustrated below.
• LH enters the testes and stimulates the interstitial cells of Leydig to make and release testosterone into the testes and the blood.
• Testosterone, the hormone responsible for the secondary sexual characteristics that develop in the male during adolescence, stimulates spermatogenesis. These secondary sex characteristics include a deepening of the voice, the growth of facial, axillary, and pubic hair, and the beginnings of the sex drive.
• The hypothalamus releases GnRN, causing the anterior pituitary to release LH and FSH. FSH and LH both act on the testes.

• FSH stimulates the Sertoli cells in the testes to facilitate spermatogenesis and to secrete inhibin.
• LH causes the Leydig cells in the testes to secrete testosterone. Testosterone further stimulates spermatogenesis by the Sertoli cells but inhibits GnRH, LH, and FSH production by the hypothalamus and anterior pituitary. Inhibin secreted by Sertoli cells also inhibits FSH and LH production by the anterior pituitary.
• The Sertoli cells produce the hormone inhibin, which is released into the blood when the sperm count is too high.
• This inhibits the release of GnRH and FSH, which will cause spermatogenesis to slow down. If the sperm count reaches 20 million/ml, the Sertoli cells cease the release of inhibin, and the sperm count increases.