Chapter 33: The ureter, bladder and urethra
The upper half of the ureter is in the abdomen proper; the lower half is in the pelvis. The ureter descends retroperitoneally on the lateral pelvic wall. At the level of the ischial spine, it turns forward and medially. In the male, the ureter lies in the sacrogenital fold and is crossed medially by the ductus deferens. In the female, the ureter is at first related to the posterior border of the ovary; it then lies in the uterosacral ligament and is crossed anteriorly by the uterine artery. It passes about 2 cm lateral to the cervix uteri (and hence may be endangered in hysterectomy) and courses in front of the lateral border of the vagina. A ureteric stone at this level may even be palpable per vaginam. On entering the back of the bladder, the ureter is embedded for about 2 cm in the wall of that organ. There the ureteric lumen is narrowest, and the muscular coats of the ureter and bladder are continuous. The slit-like opening ofthe ureter on the trigone may be catheterized through a cystoscope, and a radio-opaque medium may be injected (ascending, or retrograde, pyelography). Alternatively, the ureters may be examined after injection of a radio-opaque medium into the blood stream (descending, or intravenous, pyelography).
The bladder (L., vesica; hence the adjective vesical) varies in size, shape, and position with the amount of contained urine (figs. 33-1, 33-2, and 38-2). The empty bladder in vivo lies almost entirely within the pelvis and rests on the pubis and pelvic floor. As the organ fills, it ascends into the abdomen proper and may reach the level of the umbilicus. In infancy, however, even the empty bladder lies mostly within the abdomen proper.
The empty bladder is less rounded and is commonly said to have four surfaces: superior, right and left inferolateral, and posterior (or base) (fig. 33-2). The superior surface and the upper part of the base are covered by peritoneum. As the bladder fills and ascends, the peritoneum is lifted off the abdominal wall; hence the reflection becomes higher. The peritoneal relations are important in rupture of the bladder, which may result in either intraperitoneal or extraperitoneal extravasation of urine (see fig. 33-1). Behind, the peritoneum forms the rectovesical (or uterovesical) pouch (see fig. 31-9). The superior surface is related to the intestine and the body of the uterus. The inferolateral surfaces are related to the retropubic space, which contains veins and a pad of fat. The base faces backward and downward and is related to the seminal vesicles, ductus deferentes, and rectum or to the vagina and supravaginal cervix.
The apex of the bladder is connected to the umbilicus by the median umbilical ligament, which is a remnant of the urachus. The bladder is connected to the umbilicus also by the right and left medial umbilical ligaments, which are the obliterated umbilical arteries (see fig. 25-9). The main part of the bladder is termed its body. The lowest part, or neck, of the bladder is attached to the pelvic diaphragm and is continuous in the male with the prostate. This region is anchored by localized thickenings of the superior fascia of the pelvic diaphragm: the medial and lateral puboprostatic (or pubovesical) ligaments. Another fascial support, the lateral ligament, extends backward on each side from the base of the bladder to the sacrogenital fold.
The triangular area formed between the orifices of the right and left ureters and the internal urethral orifice is termed the trigone. Its mucosa is smooth, flat, red to pink, and firmly attached. Muscle fibers between the two ureteric orifices raise a fold known as the interureteric ridge. Behind the internal urethral orifice, a median fold (the uvula) formed by muscle fibers, the middle lobe of the prostate, or by both may develop with increasing age. The interior of the bladder may be viewed in vivo by an electrically lit instrument termed a cystoscope. Access to the bladder may be gained by either urethral catheterization or suprapubic puncture (see fig. 33-1). A calculus may be removed through a suprapubic incision (lithotomy). Perineal lithotomy ("cutting for stone") is a very ancient operation.
The bladder is supplied mainly by the superior and inferior vesical arteries, which arise directly or indirectly from the internal iliac artery. The veins drain into the internal iliac vein. The lymphatic vessels go to the various iliac nodes.
Innervation (fig. 33-3).
The bladder is supplied by branches of the vesical and prostatic plexuses, which are extensions of the inferior hypogastric plexuses. The branches include (1) parasympathetic motor fibers to the detrusor (i.e., the muscular coat); (2) sensory fibers that are stimulated by stretching, causing a sensation of fullness and activating reflexes; and (3) sympathetic fibers to blood vessels.
Micturition (or urination) is preceded by contraction of the diaphragm and abdominal wall. The neck of the bladder descends, the detrusor contracts reflexly, and urine is expelled from the bladder.
The urethra is a fibromuscular tube that conducts urine from the bladder (and semen from the ductus deferens) to the exterior. It begins at the neck of the bladder, traverses the pelvic and urogenital diaphragms, and ends at the external urethral orifice.
The female urethra, about 4 cm in length, is fused with the anterior wall of the vagina. It ends between the clitoris and the vagina.
The male urethra, about 20 cm in length, comprises three parts: prostatic, membranous, and spongy (see figs. 34-1 and 38-4). The prostatic part, which is the most dilatable, descends through the prostate. Its posterior wall presents a median ridge, the urethral crest, the summit of which is termed the colliculus seminalis (or the verumontanum). A diverticulum, the prostatic utricle (probably corresponding to portions of the uterus and vagina) opens on the colliculus, as do the ejaculatory ducts. The prostatic ducts open into a groove, the prostatic sinus, on each side of the urethral crest. The membranous part descends from the apex of the prostate to the bulb of the penis and is surrounded by the sphincter urethrae. The lowermost part of the membranous urethra is liable to rupture or to penetration by a catheter. The spongy part lies in the corpus spongiosum and traverses the bulb, body, and glans of the penis. It is slightly dilated near its origin (intrabulbar fossa) and termination (navicular fossa). The two bulbourethral glands (which are situated bilaterally in the sphincter urethrae and behind the membranous urethra) open into the proximal portion of the spongy urethra. The external urethral orifice is the narrowest portion of the entire urethra. The interior of the urethra may be viewed in vivo by an electrically lit instrument termed a urethroscope.
33-1 How does the distended bladder differ from the empty organ?
33-2 How does the bladder of a child differ from that of an adult?
33-3 How does the trigone differ from the rest of the bladder?
33-4 What is lithotomy?
33-5 Which is the narrowest portion of the urethra?
33-6 Which structures open into the urethra?
Figure 33-1 The urinary bladder empty (A) and full (B). The peritoneum is stripped away from the anterior abdominal wall as the bladder fills. Hence access to a full bladder may be gained extraperitoneally (t, trocar; in B). Rupture may be intraperitoneal (i) or extraperitoneal (e). In A, the prostate is being palpated per rectum. (Based on Testut and Latarjet.)
Figure 33-2 The bladder and urethra. A, Posterior view, showing the prostate and seminal vesicles. B, Right lateral view. The blue areas are those covered by peritoneum. C, Coronal section, showing the trigone and colliculus seminal is on the posterior walls of the bladder and urethra, respectively. Cf. Fig. 34-3A.
Figure 33-3 Nerve supply of the urinary bladder and related structures. The preganglionic parasympathetic fibers (interrupted lines) to the smooth muscle (detrusor) of the bladder synapse with ganglion cells in the wall of the organ. Most of the afferent fibers (blue) from the bladder and urethra course in the pelvic splanchnic nerves. A few pain fibers from the bladder ascend in the hypogastric plexuses to the upper lumbar part of the spinal cord. The sympathetic supply is not shown. Pain fibers from the urethra course in the pelvic splanchnic and pudendal nerves. The red lines represent motor fibers to the levator ani and sphincter urethrae.