Anal Canal

Anal Canal

The anal canal is the terminal part of the large intestine. It is situated between the rectum and anus, below the level of the pelvis. It is approximately 3.5 centimeters long and is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincter muscles that keep the lumen closed in the form of an anteroposterior slit. It is lined by squamous epithelium, which is capable of both absorptive and secretory functions.

Anatomy

The anal canal starts at the rectum and ends at the anus. It is the final pathway for the elimination of fecal material from the body. The canal is divided into three parts: the upper part, the middle part, and the lower part. The upper part is lined by rectal columnar epithelium, the middle part is lined by transitional epithelium, and the lower part is lined by stratified squamous epithelium.

Function

The primary function of the anal canal is to control the expulsion of feces from the body. The internal and external sphincter muscles allow the anal canal to maintain continence. When the rectum is full, the increase in intra-rectal pressure forces the walls of the anal canal apart allowing for defecation to occur.

Clinical significance

Diseases and conditions that affect the anal canal can cause pain, bleeding, and other symptoms. These include hemorrhoids, anal fissures, anal cancer, and anal abscesses. Diagnosis of these conditions often involves a digital rectal exam or an anoscopy. Treatment can involve medication, dietary changes, or surgery, depending on the severity and nature of the condition.

See also

• Digestive system
• Large intestine
• Defecation