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Urethra and Penis


Urethra and Penis
The figure shows the entire length of the male urethra as it traverses the prostate, pelvic diaphragm, and the penis. The natural curvature (see Plate 2-1) of the penis has been removed. The fascial relationships among tissues in the penis are not emphasized here but can be found in Plates 2-2 through 2-4. The pendulous, or penile urethra, and bulbous urethra extend through the center of the spongy tissue called the corpus spongiosum that joins with the paired corpora cavernosa to form the penile shaft. Each of the three spongy bodies is enclosed in a fibrous capsule, the tunica albuginea (see lower portion of Plate 2-3). The cavernosal and spongiosal bodies have a separate blood supply and there are normally no vascular anastomoses between them. Vascular shunts between these bodies may occur with trauma, however. The spongy tissue of the corpora cavernosa and spongiosum is composed of large venous sinuses that become widely dilated and engorged with blood during penile erection.

The urethral epithelium varies in different anatomic segments of the urethra. From the bladder neck to the triangular ligament (pars prostatica), the funnel-shaped coning of the trigone as it progresses distally into the prostatic urethra, the epithelium is transitional in character. In the membranous urethra (pars membranacea) that traverses the urogenital diaphragm, the epithelium assumes a stratified columnar form. The epithelium of the penile urethra (pars cavernosa) is composed of pseudostratified and columnar cells. Distally, in the fossa navicularis, the epithelial cells are stratified squamous in nature. The urethral mucosa is surrounded by the lamina propria that consists of areolar tissue with venous sinuses and bundles of smooth, unstriated muscle.
Urethra and Penis

The floor of the prostatic urethra contains numerous orifices that represent the terminal ducts of the prostatic acini. Also on the prostatic urethral floor is an obvious elevation called the verumontanum, colliculus seminalis, or prostatic utricle. This mound of tissue contains a small pocket or utricle that represents the fused ends of each of the müllerian ducts (see Plate 1-2). In fact, the utricle is considered the male remnant of the female uterus. Just distal and lateral to the utricle are the slit-like orifices of the paired ejaculatory ducts, the obstruction of which is a well-defined cause of male infertility.
Within the penile periurethral tissue are many small, branched, tubular glands, the epithelia of which contain modified columnar, mucus-secreting cells. These glands of Littré are more numerous in the roof than the floor of the penile urethra. Also found in the roof of the penile urethra are many small recesses called the lacunae of Morgagni, into which the glands of Littré empty. These lacunae and glands may become chronically infected following urethritis, resulting in recurring symptoms and urethral discharge.
The pea-sized bulbourethral glands of Cowper lie laterally and posteriorly to the membranous urethra between the fasciae and the urethral sphincter within the urogenital diaphragm (see Plate 2-5). The ducts of these glands, about an inch long, pass obliquely forward and open on the floor of the bulbous urethra. The secretions from these glands form part of the seminal fluid during ejaculation.