Sphincter ani

Sphincter ani is a group of muscles situated around the anus in the human body. These muscles are responsible for controlling the expulsion of feces from the body. The sphincter ani is divided into two parts: the Sphincter ani externus and the Sphincter ani internus.

Anatomy

The sphincter ani externus is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the skin surrounding the margin of the anus. The sphincter ani internus is a muscular ring which surrounds about 2.5 cm of the anal canal; its inferior border is in contact with, but slightly above, the upper border of the external sphincter.

Function

The primary function of the sphincter ani muscles is to provide control over the expulsion of feces from the body. The internal sphincter is involuntary, meaning it contracts without conscious control. Conversely, the external sphincter is voluntary, allowing for conscious control over the passage of feces.

Clinical significance

Dysfunction of the sphincter ani muscles can lead to conditions such as fecal incontinence and anal fissure. Fecal incontinence is the inability to control bowel movements, causing stool to leak unexpectedly from the rectum. An anal fissure is a small tear in the thin, moist tissue (mucosa) that lines the anus.

See also

• Anus
• Fecal incontinence
• Anal fissure