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The urethral sphincters are two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are either the male or female external urethral sphincter and the internal urethral sphincter .
The muscle helps maintain continence of urine along with the internal urethral sphincter which is under control of the autonomic nervous system.The external sphincter muscle prevents urine leakage as the muscle is tonically contracted via somatic fibers that originate in Onuf's nucleus and pass through sacral spinal nerves S2-S4 then the pudendal nerve to synapse on the muscle.
During urination, the detrusor muscle contracts, the external urinary sphincter and muscles of the perineum relax, and urine flows through the urethra [13] and exits the penis or vulva through the urinary meatus. [11] The urge to pass urine stems from stretch receptors that activate when between 300 - 400 mL urine is held within the bladder. [13]
The external urethral sphincter is a striated muscle that allows voluntary control over urination. [5] The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, receives its nerve supply by the sympathetic division of the autonomic nervous system. [6] The internal sphincter is present both in males ...
When the external urinary sphincter is relaxed urine is released from the urinary bladder when the pressure there is great enough to force urine to flow out of the urethra. The micturition reflex normally produces a series of contractions of the urinary bladder. The flow of urine through the urethra has an overall excitatory role in micturition ...
The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle , [ 1 ] [ 2 ] but anatomically and functionally fully independent from it. [ 3 ]
Conditions involving low output of urine are oliguria (< 400 mL/day) and anuria (< 100 mL/day). The first step in urine formation is the filtration of blood in the kidneys. In a healthy human, the kidney receives between 12 and 30% of cardiac output , but it averages about 20% or about 1.25 L/min.
The American Urological Association reports studies showing rates as low as 7% to as high as 27% in men and rates as low as 9% to 43% in women. [1] Urge incontinence was reported as higher in women. [1] Older people are more likely to be affected, and the number of symptoms increases with age. [1]