Page 130 - Clinical Anatomy

ECA2 7/18/06 6:43 PM Page 115

The urinary tract 115

The urethra
The male urethra (Fig. 87b)

The male urethra is 8in (20cm) long and is divided into the prostatic, mem-
branous and spongy parts.
The prostatic urethra (1.25in (3cm)), as its name implies, traverses the
prostate. Its posterior wall bears a longitudinal elevation termed the ure-
thral crest, on each side of which is a shallow depression, the prostatic sinus,
into which the 15–20 prostatic ducts empty. At about the middle of the crest
is a prominence termed the colliculus seminalis (verumontanum) into which
opens the prostatic utricle. This is a blind tract, about 5mm long, running
downwards from the substance of the median lobe of the prostate. It is
believed to represent the male equivalent of the vagina, a remnant of the
paramesonephric duct (see page 148). On either side of the orifice of the
prostatic utricle open the ejaculatory ducts, formed by the union of the duct
of the seminal vesicle and the terminal part of the vas deferens.
The membranous urethra (0.75in (2cm)) pierces the external sphincter
urethrae (the voluntary sphincter of the bladder) and the fascial perineal
membrane which covers the superficial aspect of the sphincter.
The spongy urethra (6in (15cm)) traverses the corpus spongiosum of the
penis. It first passes upwards and forwards to lie below the pubic symph-
ysis and then in its flaccid state bends downwards and forwards.

Clinical features

1◊◊Where the urethra passes beneath the pubis is a common site for it to be
ruptured by a fall astride a sharp object, which crushes it against the edge of
the symphysis.
2◊◊The external orifice is the narrowest part of the urethra and a calculus
may lodge there. Immediately within the meatus, the urethra dilates into a
terminal fossa whose roof bears a mucosal fold (the lacuna magna) which
may catch the tip of a catheter. Instruments should always be introduced
into the urethra beak downwards for this reason.

The female urethra

The female urethra is 1.5in (4cm) long; it traverses the sphincter urethrae
and lies immediately in front of, indeed embedded in the wall of, the
vagina. Its external meatus opens 1in (2.5cm) behind the clitoris. The
sphincter urethrae in the female is a tenuous structure and vesical control
appears to depend mainly on the intrinsic sphincter of condensed circular
muscle fibres of the bladder.

The mucosa of the urinary tract
The pelvis, ureter, bladder and urethra are lined by a transitional