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Muscles keeping urine in the bladder From Wikipedia, the free encyclopedia
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. When either of these muscles contracts, the urethra is sealed shut.
The external urethral sphincter originates at the ischiopubic ramus and inserts into the intermeshing muscle fibers from the other side. It is controlled by the deep perineal branch of the pudendal nerve. Activity in the nerve fibers constricts the urethra.
In males and females, both internal and external urethral sphincters function to prevent the release of urine. The internal urethral sphincter controls involuntary urine flow from the bladder to the urethra, whereas the external urethral sphincter controls voluntary urine flow from the bladder to the urethra.[2] Any damage to these muscles can lead to urinary incontinence. In males, the internal urethral sphincter has the additional function of preventing the flow of semen into the male bladder during ejaculation.[3]
Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, the urethrovaginal muscle, and the compressor urethrae. The urethrovaginal muscle fibers wrap around the vagina and urethra and contraction leads to constriction of both the vagina and the urethra. The origin of the compressor urethrae muscle is the right and left inferior pubic ramus and it wraps anteriorly around the urethra so when it contracts, it squeezes the urethra against the vagina. The external urethrae, like in males, wraps solely around the urethra.[4]
Congenital abnormalities of the female urethra can be surgically repaired with vaginoplasty.[5]
The urethral sphincter is considered an integral part of maintaining urinary continence, and it is important to understand its role in some conditions:
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