Urinary Bladder. Prof. Imran Qureshi

Transcription

1 Urinary Bladder Prof. Imran Qureshi Urinary Bladder It develops from the upper end of the urogenital sinus, which is continuous with the allantois. The allantois degenerates and forms a fibrous cord in the adult called the urachus. The trigone of the bladder is formed by the incorporation of the lower end of the mesonephric ducts into the posterior wall of the urogenital sinus. It is a hollow viscus with strong muscular walls. When empty, it lies in the true / lesser pelvis, behind and slightly superior to the pubic bones. It is separated from these bones by a space called the retropubic space (of retzius). It lies inferior to the peritoneum and rests on the pelvic floor. The bladder is relatively free within the extraperitoneal subcutaneous fatty tissue. Only its neck is held firmly by the lateral ligaments of the bladder and the tendinous arch of pelvic fascia, especially the puboprostatic ligament in males and the pubovesical ligament in females. As it fills, it ascends superiorly into the extraperitoneal fatty tissue of the anterior abdominal wall and enters the true / greater pelvis. A full bladder may ascend to the level of the umbilicus. An empty bladder is roughly tetrahedral in shape. Externally it has an apex, a body, a fundus, and a neck. The four surfaces are a superior, two inferolateral, and a posterior. The apex of the bladder faces anteriorly and points toward the superior edge of the pubic symphysis.

2 The fundus of the bladder lies opposite the apex, and is formed by the fairly convex posterior wall. The body of the bladder is the part between the apex and the fundus. In females, the fundus is closely related to the anterior wall of the vagina. In males, it is related to the rectum. The neck of the bladder is the region where the fundus and inferolateral surfaces converge inferiorly. Its bed is formed on each side by the pubic bones and the fascia covering the obturator internus and levator ani muscles and posteriorly by the rectum or vagina. It is enveloped by loose connective tissue, the vesical fascia. Only its superior surface is covered by peritoneum. Blood supply Blood is supplied from the superior and inferior vesical branches of the internal iliac artery. The vesical veins form a plexus which drains into the internal iliac vein. Lymph drainage Lymphatics drain alongside the vesical blood vessels to the iliac and then para-aortic nodes. Nerve supply Efferent Parasympathetic fibres from S 2 to S 4 accompany the vesical arteries to the bladder. They convey motor fibres to the muscles of the bladder wall and inhibitory fibres to its internal sphincter. Sympathetic efferent fibres are said to be inhibitory to the bladder muscles and motor to its sphincter, although they may be mainly vasomotor in function, so that normal filling and emptying of the bladder are probably controlled exclusively by its parasympathetic innervation. The external sphincter is made up of striated muscle. It is also concerned in the control of micturition and is supplied by the pudendal nerve (S 2, 3, 4 ). Sensory fibres from the bladder, which are stimulated by distension, are conveyed in both the sympathetic and parasympathetic nerves, the latter pathway being the more important.

3 Relations Anteriorly the pubic symphysis. Superiorly the bladder is covered by peritoneum with coils of small intestine and sigmoid colon lying against it. In the female, the body of the uterus flops against its posterosuperior aspect. Posteriorly In the male the rectum, the termination of the vasa deferens and the seminal vesicles. In the female, the vagina and the supravaginal part of the cervix. Laterally the levator ani and obturator internus. The neck of the bladder fuses with the prostate in the male. In the female it lies directly on the pelvic fascia surrounding the short urethra. The muscle coat of bladder is formed by a crisscross arrangement of bundles.the circular component of the muscle coat condenses as an (involuntary) internal urethral sphincter around the internal orifice. The walls of the bladder are composed chiefly of the detrusor muscle. Toward the neck of the male bladder, its muscle fibers form the involuntary internal urethral sphincter. This sphincter contracts during ejaculation to prevent retrograde ejaculation of semen into the bladder. Some fibers run radially and assist in opening the internal urethral orifice. In males, the muscle fibers in the neck of the bladder are continuous with the fibromuscular tissue of the prostate. In females, these fibers are continuous with muscle fibers in the wall of the urethra. The ureteric orifices and the internal urethral orifice are at the angles of the trigone of the bladder. The ureteric orifices are encircled by

4 loops of detrusor musculature that tighten when the bladder contracts to assist in preventing reflux of urine into the bladder. At the apex of its trigone it has a small eminence called the uvula, which is, projecting into the orifice of the urethra. On either side of the bladder the peritoneum shows a depression, named the paravesical fossa. Ligaments. The bladder is connected to the pelvic wall by the endopelvic fascia. In front this fascial attachment is strengthened by a few muscular fibers, the Pubovesicales, which extend from the back of the pubic bones to the front of the bladder; behind, other muscular fibers run from the fundus of the bladder to the sides of the rectum, in the sacrogenital folds, and constitute the rectovesicales. Anteriorly there are three folds: The midian umbilical fold on the midian umbilical ligament, and two lateral umbilical folds on the obliterated umbilical arteries. The reflections of the peritoneum on to the side walls of the pelvis form the lateral false ligaments. Similar reflections of peritoneum posteriorly constitute posterior false ligaments (sacrogenital folds).

5 Applied (Cystoscopy) The interior of the bladder and its three orifices (the internal urethral meatus and the two ureteric openings) can easily inspected by means of a cystoscope. The ureteric orifices lie 1 in (2.5 cm) apart in the empty bladder, but when this is distended for cystoscopic examination, the distance increases to 2 in (5 cm). The submucosa and mucosa of most of the bladder are only loosely adherent to the underlying muscle and are thrown into folds when the bladder is empty, smoothing out during distension of the organ. Over the trigone, the triangular area bounded by the ureteric orifices and the internal meatus, the mucosa is adherent and remains smooth even in the empty bladder. Between the ureters, a raised fold of mucosa can be seen called the interureteric ridge which is produced by an underlying bar of muscle.