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 uterus by the vesicouterine excavation.
Detrusor muscle
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. If the amount of urine reaches 100% of the urinary bladder volume, the voluntary sphincter becomes involuntary and the urine will be ejected instantly. The body cannot afford having the urinary bladder burst.
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.
Since the urinary bladder has a transitional epithelium, compared to the intestine mucosa, the urinary bladder does not produce mucus. [1]
Fundus
The fundus of the urinary bladder is the superior surface of the bladder. It is lymphatically drained by the external iliac lymph nodes. The peritoneum lies superior to the fundus.
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Additional images
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Organs of the female reproductive system.
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Coronal section of pelvis, showing arrangement of fasciæ. Viewed from behind.
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Dissection of side wall of pelvis showing sacral and pudendal plexuses. (Bladder visible at lower left.) |
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The peritoneum of the male pelvis.
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Median sagitta section of male pelvis.
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Male pelvic organs seen from right side.
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Median sagittal section of female pelvis.
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Vertical section of bladder wall.
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Fundus of the bladder with the vesiculæ seminales.
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Vertical section of bladder, penis, and urethra.
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Female pelvis and its contents, seen from above and in front.
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Topography of thoracic and abdominal viscera.
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The bladder can be seen highlighted in yellow in the illustration.
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Layers of the urinary bladder wall and cross section of the detrusor muscle.
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