Rectum

The rectum is an organ belonging to the digestive system.

Function of the rectum

The rectum is the terminal part of the colon which opens into the anus. The anal sphincter enables storage of a faecal matter in the rectal ampulla before it is excreted.

The rectum is involved in continence, mostly unconscious. Contraction of the rectal ampulla is usually inhibited and the anal sphincter is contracted. The muscles of the rectal ampulla contract during defecation and the sphincter relaxes. However, the mechanism may be consciously inhibited by voluntary contraction of the sphincter.

Structure of the rectum

Despite the etymology of the word, which means "straight" in Latin, the rectum is in fact curved. It is approximately 15 centimetres long. The rectal ampulla itself is approximately 5 centimetres in length.

The rectum is vascularised by three pairs of veins and three pairs of arteries. It also contains lymph vessels.