uretrasfinktern

Uretrasfinktern, commonly referred to as the urethral sphincter, is a muscular mechanism surrounding the urethra that regulates urine flow. In humans it comprises two distinct components with interrelated functions: the internal urethral sphincter and the external urethral sphincter. Together, they help maintain continence and coordinate the act of urination.

The internal urethral sphincter is formed by smooth muscle at the bladder neck. It remains tonically contracted during the storage phase to prevent leakage and relaxes during voiding to allow urine to pass. Its activity is primarily modulated by autonomic (predominantly sympathetic) pathways and local reflexes that respond to bladder filling and bladder outlet resistance.

The external urethral sphincter consists of striated muscle under voluntary control via the pudendal nerve. It provides conscious continence by tightening the urethral opening and can be voluntarily relaxed to initiate urination. In males, portions of the sphincter interact with the prostatic and penile segments of the urethra; in females, the sphincter surrounds the distal urethra as part of the pelvic floor musculature.

Clinical relevance includes the role of the urethral sphincters in urinary continence and retention. Dysfunction or injury to these muscles, such as after pelvic surgery or childbirth, can contribute to incontinence. Management options range from pelvic floor rehabilitation to surgical interventions, including the use of artificial urinary sphincters or other procedures to restore sphincter competence. Understanding sphincter function is also important in evaluating voiding disorders such as detrusor-sphincter dyssynergia.