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urinary sphincter

(urethral sphincter) A muscular structure that regulates the outflow of urine from the bladder into the urethra. When the muscles contract, the urethra narrows, and urination stops or slows. Therefore, it is critical for the maintenance of urinary continence. (Compositions) • internal urethral sphincter • external urethral sphincter (Internal urethral sphincter) • Located at the bladder's inferior end and the urethra's proximal end at the junction of the urethra with the urinary bladder, a continuation of the detrusor muscle. It remains relaxed to allow the bladder to store urine, and contracts during urination to release urine. • It is made of smooth muscle, therefore, it is under involuntary control of the autonomic nervous system. • This is the primary sphincter for prohibiting the release of urine. (External urethral sphincter) • Located in the deep perineal pouch, at the bladder's distal inferior end in females, and inferior to the prostate (at the level of the membranous urethra) in males. • It is made of skeletal muscle, therefore, it is under voluntary control of the somatic nervous system. • It is a secondary sphincter to control the flow of urine through the urethra. Neurogenic bladder dysfunction is characterized by overactive bladder, urinary urgency, frequency, incontinence, or difficulty passing urine, due to disease or injury of the central nervous system or peripheral nerves involved in the control of urination.