An external sphincter is a skeletal muscle that forms a ring-like structure around a bodily passage, controlling its opening and closing. These muscles are under voluntary control, meaning an individual can consciously decide when to contract or relax them. This voluntary regulation plays a role in maintaining continence and regulating the release of substances from the body.
Locations and Primary Functions
The human body features two primary external sphincters: the external anal sphincter and the external urethral sphincter. The external anal sphincter is an oval tube of skeletal muscle fibers that encircles the anal canal. This muscle is responsible for providing voluntary control over defecation, allowing individuals to consciously hold in stool or release it.
The external urethral sphincter is located in the pelvic floor, surrounding the urethra. In males, it is situated at the level of the membranous urethra, while in females, it is positioned around the mid-urethra. This sphincter’s primary role is to maintain urinary continence by regulating the flow of urine from the bladder, enabling conscious control over urination. Both external sphincters are therefore fundamental for maintaining continence.
How External Sphincters Work
External sphincters operate as skeletal muscles. The brain sends signals through the somatic nervous system to the pudendal nerve, which then innervates these muscles, prompting them to contract or relax. This neural pathway allows for intentional control over defecation and urination.
The external anal sphincter maintains a continuous tonic contraction at rest, preventing the involuntary passage of feces. When the rectum fills and the internal anal sphincter (an involuntary muscle) relaxes, the external anal sphincter can be consciously tightened to delay defecation. Similarly, the external urethral sphincter contracts to keep the urethra sealed, preventing urine leakage, and relaxes voluntarily to allow urination. This coordinated action ensures precise control over bodily elimination.
Common Issues and Causes
Dysfunction of external sphincters can lead to various issues. Urinary incontinence, characterized by involuntary urine leakage, is a common problem. This can manifest as stress incontinence, where leakage occurs with activities like coughing or sneezing due to sphincter weakness, or urge incontinence.
Fecal incontinence, the inability to control bowel movements, is another concern. This can range from mild leakage of gas or liquid stool to complete loss of bowel control. Issues can also include retention, where the sphincter may not relax properly, hindering elimination. Common causes of external sphincter dysfunction include aging, which can lead to muscle weakness, and childbirth, which can cause injury or stretching of the pelvic floor muscles and nerves, such as the pudendal nerve. Nerve damage from neurological disorders or injuries to the lower spine, as well as surgical procedures in the pelvic area, can also impair sphincter function.
Maintaining External Sphincter Health
Maintaining the health of external sphincters involves lifestyle choices and targeted exercises. A healthy weight reduces strain on pelvic floor muscles, which support sphincter function. Staying hydrated and consuming a fiber-rich diet helps prevent constipation, which can stress the anal sphincters during straining.
Specific exercises, particularly Kegel exercises, strengthen the pelvic floor muscles. These exercises involve consciously squeezing and lifting the muscles around the anus and urethra, holding the contraction for a few seconds, and then relaxing. Consistent practice can improve muscle strength and control over time, helping to prevent or alleviate incontinence. If persistent issues arise, seeking medical advice from a healthcare professional is important for diagnosis and treatment.