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In the anatomy of mammals, the urinary bladder 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.
Anatomy The urinary bladder is a hollow, muscular and distensible or elastic organ that sits on the pelvic floor (superior to the prostate in males). On its anterior border lies the pubic symphysis and, on its posterior border, the vagina (in females) and rectum (in males). The urinary bladder can hold approximately 17 to 18 ounces (500 to 530 ml) of urine, however the desire to micturate is usually experienced when it contains about 5 to 7 ounces (150 to 200 ml). The ureters enter the bladder diagonally from its dorsolateral floor in an area called the trigone. The trigone is a triangular shaped area on the postero-inferior wall of the bladder. The urethra exits at the lowest point of the triangle of the trigone. Detrusor muscle The detrusor muscle is a layer of the urinary bladder wall, made up of smooth muscle fibers. When the bladder is stretched, this signals the parasympathetic nervous system to cause contraction of the detrusor muscle. This then encourages the bladder to expel urine through the urethra. For the urine to finally 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 study of the functional aspects of the detrusor muscle is urodynamics. The wall of the urinary bladder consists of three layers: Diseases of the bladder See also Additional images Image:Illu urinary system.jpg|Urinary system | |||||||||||||||||||||||||||||||||||||
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