Review the anatomy of the male genitalia.
Review the anatomy of the male genitalia.
The shaft of the penis is formed by three columns of vascular erectile tissue: the corpus spongiosum, containing the urethra, and two corpora cavernosa. The corpus spongiosum forms the bulb of the penis, ending in the cone-shaped glans with its expanded base, or corona. In uncircumsized men, the glans is covered by a loose, hoodlike fold of skin called the prepuce or foreskin where smegma, or secretions of the glans, may collect. The urethra is located ventrally in the shaft of the penis; urethral abnormalities may sometimes be felt there. The urethra opens into the vertical, slitlike urethral meatus, located somewhat ventrally at the tip of the glans.
The scrotum is a loose, wrinkled pouch divided into two compartments, each of which contains a testis or testicle. The testes are ovoid, somewhat rubbery structures, about 4.5 cm long in the adult, with a range from 3.5 cm to 5.5 cm. The left usually lies somewhat lower than the right. On the posterolateral surface of each testis is the softer, comma-shaped epididymis. It is most prominent along the superior margin of the testis. The epididymis may be located anteriorly in 6% to 7% of males. Surrounding the testis, except posteriorly, is the tunica vaginalis, a serous membrane enclosing a potential cavity.
The testes produce spermatozoa and testosterone. Testosterone stimulates the pubertal growth of the male genitalia, prostate, and seminal vesicles. It also stimulates the development of masculine secondary sex characteristics, including the beard, body hair, musculoskeletal development, and enlarged larynx with the associated low-pitched voice.
The vas deferens, a cordlike structure, begins at the tail of the epididymis, ascends within the scrotal sac, and passes through the external inguinal ring on its way to the abdomen and pelvis. Behind the bladder it is joined by the duct from the seminal vesicle and enters the urethra within the prostate gland. Sperm thus pass from the testis and the epididymis through the vas deferens into the urethra. Secretions from the vasa deferentia, the seminal vesicles, and the prostate all contribute to the semen. Within the scrotum each vas is closely associated with blood vessels, nerves, and muscle fibers. These structures make up the spermatic cord.
Male sexual function depends on normal levels of testosterone, adequate arterial blood flow to the inferior epigastric artery and its cremasteric and pubic branches, and intact neural innervation from a-adrenergic and cholinergic pathways. Erection from venous engorgement of the corpora cavernosa results from two types of stimuli. Visual, auditory, or erotic cues trigger sympathetic outflow from higher brain centers to the T11 through L2 levels of the spinal cord. Tactile stimulation initiates sensory impulses from the genitalia to S2—S4 reflex arcs and parasympathetic pathways via the pudendal nerve. Both sets of stimuli appear to increase levels of nitric oxide and cyclic GMP, resulting in local vasodilation.
Lymphatics. Lymphatics from the penile and scrotal surfaces drain into the inguinal nodes. When you find an inflammatory or possibly malignant lesion on these surfaces, assess the inguinal nodes especially carefully for en largement or tenderness. The lymphatics of the testes, however, drain into the abdomen, where enlarged nodes are clinically undetectable. See page 452 for further discussion of the inguinal nodes.
Anatomy of the Groin. Because hernias are relatively common, it is important to understand the anatomy of the groin. The basic landmarks are the anterior superior iliac spine, the pubic tubercle, and the inguinal ligament that runs between them. Find these on yourself or a colleague.
The inguinal canal, which lies above and approximately parallel to the inguinal ligament, forms a tunnel for the vas deferens as it passes through the abdominal muscles. The exterior opening of the tunnel—the external inguinal ring—is a triangular slitlike structure palpable just above and lateral to the pubic tubercle. The internal opening of the canal—or internal inguinal ring—is about 1 cm above the midpoint of the inguinal ligament. Neither canal nor internal ring is palpable through the abdominal wall. When loops of bowel force their way through weak areas of the inguinal canal they produce inguinal hernias, as illustrated on pp. 381-382.
Another potential route for a herniating mass is the femoral canal. This lies below the inguinal ligament. Although you cannot see it, you can estimate its location by placing your right index finger, from below, on the right femoral artery. Your middle finger will then overlie the femoral vein; your ring finger, the femoral canal. Femoral hernias protrude here.
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