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In anatomy, the urinary bladder is a hollow, muscular, and distensible (or elastic) organ that sits on the pelvic floor in mammals. It is the organ that collects urine excreted by the kidneys prior to disposal by urination. Urine enters the bladder via the ureters and exits via the urethra.
In males, the bladder is superior to the prostate, and separated from the rectum by the rectovesical excavation.
In females, the bladder is separated from the rectum by the rectouterine excavation, and it is separated from the uterus by the vesicouterine excavation.
Additional recommended knowledge
The wall of the urinary bladder consists of three layers:
When the urinary bladder is relaxed, the epithelium is 5-6 cell layers thick and the superficial cells bulge into the lumen. Thick rigid areas of the plasma membrane fold down within the cytoplasm are called fusiform vesicles.
When the urinary bladder is extended, the epithelium is 3-4 layers thick and has squamous epithelial cells without vesicles. The vesicles have been reinserted in the plasma membrane.
The detrusor muscle is a layer of the urinary bladder wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. When the bladder is stretched, this signals the parasympathetic nervous system to contract the detrusor muscle. This encourages the bladder to expel urine through the urethra.
For the urine to exit the bladder, both the autonomically controlled internal sphincter and the voluntarily controlled external sphincter must be opened. Problems with these muscles can lead to incontinence.
The urinary bladder usually holds 400–620 mL of urine, but it can hold twice this without rupturing if, for example, the outflow is obstructed.
The desire to urinate usually starts when the bladder reaches around 75% of its working volume. If the subject is distracted the desire can fade and return with more urgency as the bladder continues to fill.
The fundus of the urinary bladder is the bottom of the bladder. It is lymphatically drained by the external iliac lymph nodes.
Categories: Pelvis | Organs | Urology | Urinary system
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Urinary_bladder". A list of authors is available in Wikipedia.|