Urethral sphincters

Muscles controlling the flow of urine through the urethra

Diagram of the male urethra, showing the location of the urethral sphincters

The urethral sphincters are two muscles used to control the exit of urine from the urinary bladder through the urethra. These muscles are critical in maintaining urinary continence and are part of the urinary system.

Anatomy

The urethral sphincters consist of two distinct muscles: the internal urethral sphincter and the external urethral sphincter.

Internal urethral sphincter

The internal urethral sphincter is a smooth muscle that is located at the junction of the urinary bladder and the urethra. It is involuntary and controlled by the autonomic nervous system. In males, it is located at the base of the prostate gland, and it plays a role in preventing the backflow of semen into the bladder during ejaculation.

External urethral sphincter

The external urethral sphincter is a skeletal muscle that surrounds the urethra and is under voluntary control. It is part of the pelvic floor muscles and is responsible for the conscious control of urination. In females, it is located near the middle of the urethra, while in males, it is located just below the prostate gland.

Function

The primary function of the urethral sphincters is to control the release of urine from the bladder. The internal sphincter remains contracted to hold urine in the bladder, while the external sphincter provides additional control to prevent involuntary urination. During urination, the external sphincter relaxes, allowing urine to pass through the urethra and out of the body.

Clinical significance

Dysfunction of the urethral sphincters can lead to urinary incontinence, which is the involuntary leakage of urine. This can occur due to weakening of the pelvic floor muscles, nerve damage, or other medical conditions. Treatments may include pelvic floor exercises, medications, or surgery.

Related pages

• Urinary system
• Urinary incontinence
• Pelvic floor