Porth's Essentials of Pathophysiology, 4e

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Genitourinary and Reproductive Function

U N I T 1 1

Ureter

Bladder

Rectum

Seminal vesicle

Ductus deferens (vas deferens)

Prostate

Glans penis

Bulbourethral gland

Prepuce

Epididymis

FIGURE 39-1. Structures of the male reproductive system, including the testes, scrotum, and excretory ducts.

Scrotum

Testis

Testicular Function The two primary functions of the testes or male gonads are steroidogenesis, or synthesis of androgens or male sex hormones, and spermatogenesis, or sperm produc- tion. 1–3 The testes are paired ovoid organs that lie within the scrotum, which hangs outside the abdominal cavity. The testes are surrounded by two tunics. The outer tunic is the two-layered tunica vaginalis derived from the peritoneum. The inner tunic is the tunica albuginea , the dense connective tissue capsule of the testes (Fig. 39-2).

Septal extensions of the tunica albuginea divide the testes into 200 to 300 wedge-shaped compartments or lobules. Each lobule contains one to four tightly coiled seminiferous tubules, in which sperm are produced, and a connective tissue stroma, in which the androgen-producing Leydig or interstitial cells are located. Hormone Production The testes produce several male sex hormones, includ- ing testosterone, dihydrotestosterone, and androstene- dione. 1–3 Testosterone, which is the most abundant of these hormones, is considered the main testicular hor- mone. The adrenal cortex also produces androgens, albeit in much smaller quantities (<5% of the total male androgens) than the testes. Larger amounts of testosterone are formed from dihydrotestosterone and androstenedione in other tissues of the body, especially the liver. 1 In addition to testosterone, small amounts of estrogens are formed in the male. Some of this estrogen, thought to be formed from testosterone, plays an impor- tant role in spermatogenesis. Testosterone is metabolized in the liver and excreted by the kidneys. In the bloodstream, testosterone exists in an unbound (free) or a bound form. The bound form is attached to plasma proteins, including albumin and the sex hormone–binding protein produced by the liver. Only approximately 3% of circulating testosterone is unbound and therefore able to enter the cell and exert its metabolic effects. 1 Much of the testosterone that becomes fixed to the tissues is converted to dihydrotes- tosterone, especially in certain target tissues such as the prostate gland. Some of the actions of testosterone depend on this conversion, whereas others do not.

Epididymis Ductus deferens

Tunica vaginalis Rete testis

Efferent ductules

Lobules

Septum

Tunica albuginea Seminiferous tubules

FIGURE 39-2. The parts of the testes and epididymis.