Urethra function and definition
A narrow, somewhat muscular tube that carries URINE from the BLADDER to the outside of the body. The point of exit is the urinary or urethral meatus. The urethral sphincter MUSCLE at the base of the bladder controls the release of urine into the urethra. Once the urethral sphincter relaxes to let urine pass, the urine flows to the outside of the body until the bladder empties and the urethral sphincter tightens. It may take a few seconds after the sphincter closes for the residual urine in the urethra to make its way out the urethral opening. BLADDER CATHETERIZATION, CYSTOSCOPY, ureteroscopy, and intravesical therapies use the urethra to enter the urinary system (usually with sedation or ANESTHESIA, except catheterization).
In a woman the urethra is about an inch and a half long, extending from the base of the bladder to the external GENITALIA where it exits the body between the CLITORIS and the VAGINA. The urethra’s only role in a woman is to carry urine from the body. In a man the urethra is about eight inches long and extends from the base of the bladder to exit the body at the tip of the PENIS. As it exits the bladder in a man the urethra passes through the PROSTATE GLAND, which encircles the neck of the bladder. The male urethra also carries SPERM during EJACULATION. The VAS DEFERENS, the tube that carries SEMEN from the male reproductive organs, enters the urethra at the prostate gland. A valve at the base of the urethra directs the flow of either urine or semen through the urethra.
For further discussion of the urethra within the context of the urinary system’s structure and function please see the overview section “The Urinary System.”
See also EPISPADIAS; HYPOSPADIAS; RETROGRADE EJACULATION.