Sphincter urethrae

A cylindrical muscle that plays a crucial role in urine control and the regulation of urine flow.

The sphincter urethrae is a skeletal muscle located around the urethra, responsible for voluntarily controlling the release of urine from the bladder. This muscle creates a constricting action around the urethra during times when urination is not desired, thus preventing the involuntary loss of urine.

Terminologia Anatomica

sphincter-urethrae

System

Urinary system

Function

The primary function of the sphincter urethrae is to maintain continence by controlling the passage of urine through the urethra. It operates under voluntary control, allowing individuals to decide when they are ready to urinate. This mechanism is essential for both urinary function and social convenience, as it enables a person to hold urine until they can reach a suitable location to relieve themselves. During urination, the sphincter relaxes, allowing urine to flow from the urinary bladder through the urethra and out of the body. This muscle works in coordination with the bladder's detrusor muscle, which contracts to expel urine. Dysfunction of the sphincter urethrae can lead to urinary incontinence, highlighting its importance in maintaining engaged bodily control over this critical function.

Location

The sphincter urethrae is located in the pelvic region, encircling the urethra as it exits the bladder. In males, it surrounds the prostatic urethra and extends down to the membranous urethra, transitioning as it descends. In females, the sphincter is positioned more centrally in relation to the urethra, surrounding the entire length of the female urethra just below the bladder neck. While it is part of the urogenital diaphragm, its precise placement varies slightly according to sex and pelvic anatomy, which results in a unique functional significance in both males and females.

Did You Know?

The sphincter urethrae is also referred to as the external urethral sphincter, differentiating it from internal sphincters that are involuntary.
Weakness of the sphincter urethrae can contribute to postpartum urinary incontinence in women.
This muscle can be consciously controlled, allowing individuals to halt urine flow or initiate it at will.
The coordination between the sphincter urethrae and the bladder's detrusor muscle is vital for normal urination, illustrating the complexity of urinary control.