Anatomy

The urethra extends from the internal urethral orifice at the bladder neck to the external meatus. In the male it is approximately 15-20 cm long and is divided into three sections (Figure 31.1).

The prostatic urethra is 3-4 cm long, traversing the prostate in a curved manner. Throughout its length, a midline ridge on the posterior wall known as the urethral crest projects into the lumen causing it to appear crescentic on transverse section. The most prominent part of this ridge, close to the midpoint, is called the verumontanum. Here lies the orifice of the prostatic utricle, a short, blind-ending vestigial sac. The openings of the ejaculatory ducts lie on either side of the verumontanum. Prostatic ducts empty into the urethral sinuses, gutters flanking the urethral crest.

The membranous urethra extends from the prostatic apex to the bulb of the penis and measures 1 cm approximately. Small bulbourethral or Cowper's glands lie on either side and secrete into it.

Figure 31.1. Anatomy of the urethra.

The penile urethra measures 10-15 cm and is surrounded by the corpus spongiosum throughout most of its length. It includes the bulbous urethra proximally and the pendulous urethra distally. Scattered mucus-secreting (Littre's) glands are present periurethrally. The distal portion within the glans penis is dilated to form the fossa terminalis, before narrowing at the external meatus.

The female urethra is approximately 4 cm long and extends from the bladder neck to the external urethral meatus, embedded throughout its length in the adventitial coat of the anterior vaginal wall. Like the male counterpart it has a posterior midline ridge, the urethral crest, which gives a crescentic shape on sectioning, and periurethral mucus-secreting (Skene's) glands.

The urethra is lined proximally by urothelium and distally by non-keratinising stratified squamous epithelium and, in males, the intervening membranous urethra (and part of the penile urethra) by pseudostratified columnar epithelium. However, it should be noted that most urethral tissue submitted for pathological examination is diseased or altered by instrumentation and hence highly susceptible to metaplastic change.

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