THE URINARY BLADDER ANATOMY AND PHYSIOLOGY Dr. Ali Kamal M. Sami M.B.Ch.B. M.A.U.A. F.I.B.M.S. M.I.U.A.

A hollow muscular organ A reservoir for urine The adult bladder normally has a capacity of 400–500 ml.

When empty, bladder lies behind the pubic symphysis &it is a pelvic organ. In infants and children, it is situated higher. When it is full, it rises above the symphysis and can readily be palpated or percussed. When over distended, as in acute or chronic urinary retention, it may cause the lower abdomen to bulge visibly.

Extending from the dome of the bladder to the umbilicus is a fibrous cord, the median umbilical ligament, which represents the obliterated urachus.

Ureters enter the bladder posteroinferiorly are about 5 cm apart. The orifices,situated at interureteric ridge that forms the proximal border of the trigone, are about 2.5 cm apart. The trigone occupies the area between the ridge and the bladder neck.

The internal sphincter, or bladder neck, is not a true circular sphincter but a thickening formed by interlaced and converging muscle fibers of the detrusor as they pass distally to become the smooth musculature of the urethra.

RELATIONS In males, the bladder is related posteriorly to the seminal vesicles, vasa deferentia, ureters, and rectum. In females, the uterus and vagina are interposed between the bladder and rectum. The dome and posterior surfaces are covered by peritoneum. So in this area the bladder is related to the small intestine and sigmoid colon.

The bladder is related to the posterior surface of the pubic symphysis, and, when distended, it is in contact with the lower abdominal wall.

Histology The mucosa of the bladder is composed of transitional epithelium. Beneath it,is a submucosal layer formed of connective and elastic tissues Beneath it,is a submucosal layer formed of connective and elastic tissues External to the submucosa is the detrusor muscle

the detrusor muscle which is made up of a mixture of smooth muscle fibers arranged at random in a longitudinal, circular, and spiral manner without any layer formation or specific orientation Except close to the internal meatus, where the detrusor muscle assumes 3 definite layers: Inner longitudinal, middle circular, and outer longitudinal.

Blood Supply

A. ARTERIAL 1-Superior Vesical, 2-Middle Vesical, 3-Inferior Vesical arteries, which arise from the anterior trunk of the internal iliac (hypogastric)artery, 4-The obturator artery. 5-The inferior gluteal artery. In females, the 6-uterine and 7-vaginal arteries also send branches to the bladder.

B. VENOUS Surrounding the bladder is a rich plexus of veins that ultimately empties into the internal iliac (hypogastric) veins.

Lymphatics The lymphatics of the bladder drain into 1-the vesical, 2-external iliac, 3-internal iliac (hypogastric), 4-common iliac lymph nodes.

Physiology

The nerves concerned in micturition are as follows. 1- The parasympathetic input; 1- The parasympathetic input; derived from the anterior primary divisions of the second, third and fourth sacral segments ( S2,S3,S4). These fibers pass through the pelvic splanchnic nerves inferior hypo gastric plexus, from which they are distributed to the bladder. The pelvic plexus is easily damaged during excisions of the rectum, following which disturbances of micturition and sexual function may occur.

2-The sympathetic input 2-The sympathetic input ; These nerves arise in the 11th thoracic to the second lumbar segments (T11,T12,L1,L2). Pass via the presacral hypo gastric nerve and the sympathetic chains to the inferior hypo gastric plexus, which is situated lateral to the rectum, the bladder

3-Somatic innervations ; distal sphincter throughPudendal nerves inferior hypo gastric plexus. passes to the distal sphincter through the Pudendal nerves and through the inferior hypo gastric plexus.

sympathetic nerves afferent painful The sympathetic nerves convey afferent painful stimuli following over distension of the fundus, from the mucosa where they respond to touch, temperature and pain, and also from the muscle of the detrusor and lamina propria where they convey stretch information. These afferents pass via the inferior hypo gastric plexus. pelvic parasympathetics Pons midbrain Efferent fibers pass via the pelvic parasympathetics. Normal micturition is coordinated in the Pons in the midbrain where detrusor contraction is timed with inhibition of the distal sphincter mechanism.

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