CHAPTER 13: Male Reproductive System

MALE REPRODUCTIVE SYSTEM

BIG PICTURE

The male reproductive system primarily consists of the paired testes and the penis. In addition, accessory sex glands contribute to seminal fluid. The male reproductive system matures during adolescence and remains active for the remainder of the lifespan of the male.

MALE EXTERNAL GENITALIA

The external genitalia have the following structures (Figure 13-1A–D):

• Penis. The male copulatory organ, composed of erectile tissue, transports urine and semen via the urethra; the penis is highly innervated by perineal nerve branches and becomes engorged with blood and erects during stimulation. The penis erects in the anatomical position (i.e., when the penis is flaccid, its dorsal surface is positioned anteriorly). The penis consists of the following parts:

  • Glans penis. Formed by the terminal part of the corpus spongiosum; projects posteriorly over the end of the corpora cavernosa; covered by a free fold of skin called the prepuce. Circumcision is the surgical removal of the prepuce.

  • Body (corpus). The free pendulous part of the penis; contains the single corpus spongiosum and the paired corpora cavernosa.

    • Corpus spongiosum. Erectile tissue surrounding the spongy urethra (transports urine and semen) on the ventral surface of the penis; expands distally into the glans penis. During an erection, the corpus spongiosum prevents the urethra from being pinched closed, thereby maintaining the urethra open for transporting semen during ejaculation.

    • Corpora cavernosa. Paired erectile tissues that form most of the body of the penis on its dorsal surface; less pliable than the corpus spongiosum because the corpora cavernosa fill with the majority of blood during erection.

  • Root. The attached part of the penis consisting of the bulb and two crura:

    • Bulb of the penis. Attached in the midline to the perineal membrane; the bulb is the dilated root of the corpus spongiosum and is surrounded by the bulbospongiosus muscle.

    • Crura of the penis. Paired structures attached to the ischiopubic rami on either side of the bulb; the crura are the roots of the corpora cavernosa and are surrounded by the ischiocavernosus muscles.

• Testes. The primary male sex organ; produces spermatozoa and sex hormones (e.g., testosterone).

• Epididymis. Consists of a head, body, and tail; located on the superior pole of each testis; stores sperm during the maturation process.

• Ductus deferens. A thick-walled tube in the spermatic cord that transports sperm from the epididymis through the inguinal canal to the ejaculatory ducts in the prostate gland.

  • Innervation. Sympathetic nerves from the inferior hypogastric plexus cause peristaltic contractions in the thick smooth muscle wall to propel sperm during emission.

• Ejaculatory ducts. Formed by the union of the ductus deferens and ducts from the seminal vesicles. The ejaculatory ducts open into the prostatic urethra.

• Seminal vesicles. Lobular glands located on the base of the bladder. During emission and ejaculation, the seminal vesicles empty their secretions (e.g., fructose, citric acid, prostaglandins, and fibrinogen) into the ejaculatory duct as sperm ...