McKenna's Pharmacology for Nursing, 2e

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P A R T 7  Drugs acting on the reproductive system

Urinary bladder

Ureter

Urethra

Seminal vesical

Corpus cavernosum

Rectum

Corpus spongiosum

Prostate

Glans penis

Epididymis

Testis

Epididymis (body)

Scrotum

Vas deferens

Epididymis (body)

Testis

Sperm

Seminiferous tubules

Epididymis (body)

Interstitial or Leydig cells

Testosterone

FIGURE 39.4  The male reproductive system.

The Sertoli cells also produce a substance called inhibin , an oestrogen-like molecule. Upon the sensing of inhibin by the hypothalamus and anterior pituitary, a negative feedback response occurs, decreasing the circu- lating level of FSH. When the FSH level falls low enough, the hypothalamus is stimulated to again release GnRH to stimulate FSH release. This feedback system prevents overproduction of sperm in the testes (Figure 39.5). Inhibin has been investigated for many years as a possible male birth control drug because it is thought to affect only sperm production.

The LH stimulates the interstitial (Leydig) cells to produce testosterone. The concentration of testoster- one acts in a similar negative feedback system with the hypothalamus. When the concentration is high enough, the hypothalamus decreases GnRH release, leading to a subsequent decrease in FSH and LH release. The levels of testosterone are thought to remain within a fairly well-defined range of normal. With age, the seminiferous tubules and intersti- tial cells atrophy and the male climacteric, a period of lessened sexual activity and loss of testosterone effects,