The bladder

Each Urelerenters the single bladder dose to the neck. The ureters underrun the bladder mucosa for a short distance before opening into the lumen at an oblique angle. This area, known as the triρone.

The bladder is a pear-shaped hollow organ. The rounded end points cranially. while the narrow end or neck points caudally and usually lies within the pelvic cavity. Its function is to collect and store urine. When full, the bladder extends into the abdomen, pulling the neck Ventrally over the edge of the pelvic brim with the ventral surface of the bladder touching the abdominal Iloor; when empty most of the bladder lies in the pelvic cavity.

In cross-section, the bladder consists of an inner lining of Ininsitioiial epithelium which enables the walls to expand when Iilling with urine. Λ submucosal layer of elastic tissue and smooth muscle is arranged in folds to allow^r expansion. The smooth muscle Iibres are continuous with those of the internal bladder sphinc­ter. The bladder is surrounded by a layer of peritoneum which covers only the cranial end lying in the abdomen, ∕∖ll organs in the pelvic cavity arc sur­rounded by connective tissue and muscle and arc not covered in peritoneum.

The neck of the bladder ends in the bladder sphinc­ter. w hose function is to control the Ilow of urine out of the bladder and down the urethra. It consists of tw^,o concentric parts:

1. Internal sphincter - made of smooth muscle: under Involuntaryconlrol

2. External sphincter - rin% of striated muscle: under voluntary control.

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