The urethral sphincter is a muscle group that controls the release of urine from the bladder. Located at the base of the bladder, it encircles the urethra—the tube through which urine exits the body. This muscle’s primary job is to contract and close off the urethra to prevent urine from leaking out. Its proper function is fundamental for maintaining urinary continence, which is the ability to control urination. When the sphincter relaxes, it allows urine to pass from the bladder.
Anatomy of the Urethral Sphincter
The urethral sphincter is a complex composed of two distinct parts: the internal and external urethral sphincters. The internal sphincter is located at the neck of the bladder where it connects to the urethra. It is made of smooth muscle, meaning its actions are involuntary and not under conscious control. This muscle is a continuation of the bladder’s detrusor muscle, forming a ring-like structure at the bladder outlet.
The external urethral sphincter is situated further down the urethra within a region known as the deep perineal pouch. Unlike the internal sphincter, the external sphincter is composed of skeletal muscle, which is under voluntary control. This allows for the conscious decision to hold or release urine. The structure of the external sphincter is more complex in females, where it is intertwined with muscles that also constrict the vagina. In males, the external sphincter is located just below the prostate gland, and the internal sphincter is more defined, also serving to prevent semen from entering the bladder during ejaculation.
How the Sphincter Controls Urination
The control of urination is a coordinated effort between the internal and external sphincters, which function like a two-gate system. During the bladder’s filling and storage phase, the internal sphincter remains involuntarily contracted. This is regulated by the autonomic nervous system, which sends continuous signals to keep the bladder outlet securely closed as the bladder expands.
Simultaneously, the external sphincter is in a state of constant, low-level contraction, providing an additional layer of security. This muscle is governed by the somatic nervous system, which allows for conscious control. When the urge to urinate arises, the voluntary strength of the external sphincter allows a person to delay urination until it is convenient.
When a person decides to urinate, the brain sends signals through the somatic nervous system to voluntarily relax the external sphincter. This is followed by a signal from the autonomic nervous system that causes the internal sphincter to relax and the bladder’s detrusor muscle to contract. This coordinated sequence opens the urethral passage completely, allowing urine to flow out.
Causes of Sphincter Weakness or Damage
Weakening or damage of the urethral sphincter muscles can impair their ability to maintain a tight seal. Common causes include:
- Physical stress from childbirth or chronic conditions that increase abdominal pressure, such as persistent coughing or obesity.
- Surgical procedures, such as a prostatectomy in men or a hysterectomy in women, which can damage nearby muscles, supportive structures, or nerves.
- Neurological conditions like multiple sclerosis, Parkinson’s disease, or spinal cord injuries that can interfere with the communication between the brain, bladder, and sphincter.
- Age-related changes, as muscle mass and tone naturally decline over the years, which can affect the strength of the external sphincter.
Improving Sphincter Function
Strengthening the urethral sphincter, particularly the external voluntary muscle, is possible through targeted exercises and lifestyle adjustments. The most recommended method is performing Kegel exercises, which are designed to isolate and strengthen the pelvic floor muscles. To identify the correct muscles, one can try to stop the flow of urine midstream; these are the muscles to target.
Once identified, the exercises involve contracting these muscles, holding the contraction for a few seconds, and then relaxing. This should be done while breathing normally and without tightening the stomach, thigh, or buttock muscles. Regular practice with multiple repetitions performed throughout the day can gradually build muscle strength and improve urinary control.
Certain lifestyle factors can also support sphincter function. Maintaining a healthy weight reduces pressure on the bladder and pelvic floor. It is also helpful to avoid bladder irritants, such as caffeine, alcohol, and spicy foods, which can increase urinary urgency and put extra strain on the sphincter.