The urinary bladder is a hollow muscular organ that acts as a reservoir for urine. In adults, its normal capacity is 400-500 ml. The bladder lies behind the pubic bone when empty and rises into the lower abdomen when full. Blood supply comes from branches of the internal iliac artery and veins drain into the internal iliac veins. Nerves involved in micturition include the parasympathetic pelvic splanchnic nerves and sympathetic nerves from T11-L2 that innervate the detrusor muscle and distal sphincter. Coordination of micturition occurs in the pons and midbrain.

1. 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.

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

3. 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.

4. Extending from the dome of the bladder to the umbilicusis a fibrous cord, the median umbilical ligament, whichrepresents the obliterated urachus .

5. Uretersenter the bladder posteroinferiorlyare 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.

9. RELATIONS

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

18. Histology

20. Blood Supply

22. 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.

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

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

25. Physiology

26. The nerves concerned in micturition are as follows. 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.

27. 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 nerveand the sympathetic chains to the inferior hypo gastric plexus, which is situated lateral to the rectum, the bladder

28. 3-Somatic innervations; passes to the distal sphincter throughthe Pudendal nerves and through the inferior hypo gastric plexus .

29. 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. 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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