43.4A: Male Hormones
- Explain the function of male hormones in reproduction
Male Hormones
Puberty is a period of several years in which rapid physical growth and psychological changes occur, culminating in sexual maturity. The average onset of puberty is age 11 or 12 for boys. Some of the most significant parts of pubertal development involve distinctive physiological changes in individuals’ height, weight, body composition, and circulatory and respiratory systems. These changes are largely influenced by hormonal activity. Hormones play an organizational role, priming the body to behave in a certain way once puberty begins, and an activational role, referring to changes in hormones during adolescence that trigger behavioral and physical changes.
At the onset of puberty, the hypothalamus begins secreting high pulses of GnRH, or gonadotropin-releasing hormone. In response, the pituitary gland releases follicle stimulating hormone (FSH) and luteinizing hormone (LH) into the male system for the first time. FSH enters the testes, stimulating the Sertoli cells, which help to nourish the sperm cells that the testes produce, to begin facilitating spermatogenesis. LH also enters the testes, stimulating the interstitial cells, called Leydig cells, 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, or the process of sperm production in the testes. Secondary sex characteristics include a deepening of the voice, the growth of facial, axillary, and pubic hair, and the beginnings of the sex drive.
A negative feedback system occurs in the male with rising levels of testosterone acting on the hypothalamus and anterior pituitary to inhibit the release of GnRH, FSH, and LH. 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, allowing the sperm count to increase.
Key Points
- The onset of puberty is signaled by high pulses of GnRH secreted by the hypothalamus; this in turn signals the release of FSH and LH from the pituitary gland.
- FSH causes the Sertoli cells of the testes (which help nurse developing sperm cells) to begin the process of spermatogenesis in the testes.
- LH triggers the production of testosterone from the Leydig cells of the testis; testosterone causes the development of secondary sex characteristics in the male.
- As spermatogenesis and testosterone production increase, the Sertoli cells produce inhibin, which, together with rising levels of testosterone, inhibit the release of FSH and LH from the pituitary gland.
Key Terms
- puberty : the age at which a person is first capable of sexual reproduction
- Sertoli cell : a kind of sustentacular cell which serves as a “nurse” cell of the testes and which is part of a seminiferous tubule
- Leydig cell : one of the interstitial cells, located next to the seminiferous tubules inside the testicle, that produce testosterone
- follicle stimulating hormone : a gonadotropic glycoprotein hormone, secreted in the anterior pituitary, that stimulates the growth of ovarian follicles in female mammals, and induces spermatogenesis in male mammals
- luteinizing hormone : a hormone, produced by part of the pituitary gland, that stimulates ovulation and the development of the corpus luteum in female mammals, and the production of androgens by male mammals
- inhibin : a peptide hormone, secreted by the gonads, which inhibits the secretion of follicle-stimulating hormone
- testosterone : steroid hormone produced primarily in the testes of the male; it is responsible for the development of secondary sex characteristics in the male