Male Reproductive System - Testosterone
• Under the influence of FSH and testosterone, Sertoli cells produce androgen-binding protein (ABP) that binds to testosterone and maintains high levels of the hormone near spermatogenic cells. • Testosterone stimulates the final stages of spermatogenesis. • In addition, testosterone is converted into to dihydrotestosterone (DHT), another hormone that may promote sperm cell formation. • Testosterone and DHT both bind to the same intranuclear receptors. • Together, the androgens regulate male prenatal development and the development of male sexual characteristics. • Male pattern of development (before birth) • Enlargement of male sex organs and expression of male secondary sex characteristics (starting at puberty) • Anabolism (protein synthesis) Negative feedback control of testosterone • Sertoli cells release the protein hormone inhibin when the level of spermatogenesis required for male reproductive functions has been attained. • Inhibin is delivered by the blood to the gonadotrophic cells within the anterior pituitary. • Inhibin acts on the gonadotrophs to reduce FSH secretion, decreasing the rate of spermatogenesis. • Similarly, testosterone acts in a negative feedback manner on anterior pituitary gonadotrophs to suppress the secretion of LH. • The negative feedback effect of testosterone also involves its effect on the hypothalamus, which results in decreased secretion of GnRH. • Decreased secretion of GnRH causes a corresponding decrease in the secretion of both LH and FSH. • The decrease in LH causes a decrease in the secretion of testosterone by the Leydig cells in the testes. • Low levels of testosterone reduce spermatogenesis. • Conversely, an excessive decrease in testosterone allows the hypothalamus to increase its secretion of GnRH. • This secretion causes an increase in anterior pituitary secretion of LH and FSH, and an increase in secretion of testosterone by the testes.
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