Anus

The terminal opening of the digestive tract, crucial for the expulsion of feces.

The anus is the opening at the end of the digestive tract through which feces are expelled from the body. It is surrounded by sphincter muscles that control its opening and closing. This structure plays a vital role in the body's elimination processes and helps maintain continence.

Terminologia Anatomica

anus

System

Digestive system

Function

The primary function of the anus is to control the excretion of waste products from the body. It serves as the final part of the gastrointestinal tract, where the processed food material, once converted into feces, is expelled from the body. The anus is equipped with two sphincter muscles: the internal anal sphincter, which is involuntary and operates unconsciously to keep the anus closed, and the external anal sphincter, which is voluntary and allows a person to control the timing of bowel movements. This dual system is essential for maintaining bowel continence and enables the body to regulate the release of waste effectively. Additionally, the anal region is sensitive to pressure and stretch, providing feedback to the brain about the state of the rectal contents, which aids in the timing of defecation.

Location

The anus is located at the posterior end of the pelvic cavity, just below the rectum, which is the last section of the large intestine. It lies in the perineal region, between the buttocks, and is positioned slightly anterior to the sacrum. This placement allows for easy passage of feces while also being surrounded by various muscles and tissues that assist in its function. The skin covering the anus is sensitive and can vary in pigmentation, providing an important protective barrier against infection and irritation.

Did You Know?

The anus is part of a larger structure called the anal canal, which is about 2.5 to 4 centimeters long.
In addition to waste excretion, the anal region has a rich vascular supply, making it sensitive to changes and the presence of disease.
The term 'anal' comes from the Latin word 'anus,' which means 'ring' or 'circle,' reflecting the structure's cylindrical shape.
Certain medical conditions, such as hemorrhoids, can significantly affect the function and comfort of the anus, highlighting its importance in digestive health.