Large intestine

What and where is it?

The large intestine, which MedlinePlus also calls the colon, is a long hollow tube at the end of the digestive tract where the body makes and stores stool.

It consists of the colon, rectum and anal canal; it begins where the small intestine ends and is wider than it.

What it does

• Absorbing water and salts from what is left of food.
• Turning waste into stool: waste is made of undigested food, fluid and old cells shed from the lining of the digestive tract.
• Breaking down remaining nutrients with the help of bacteria, which also make vitamin K.
• Storing stool in the rectum until a bowel movement.

How it works

1. 1
   ReceptionLeftover food and fluid arrive from the small intestine.
2. 2
   Bacteria at workGut bacteria break down remaining nutrients and make vitamin K.
3. 3
   AbsorbingWater moves from the gut into the bloodstream and the waste becomes stool.
4. 4
   Moving and storingPeristalsis moves stool into the rectum, where it is stored until a bowel movement.
5. 5
   Passing stoolAn involuntary internal anal sphincter and a voluntary external sphincter control the passing of stool.

Common problems that affect it

Tumours

• Colorectal cancer.
• Colonic polyps: extra tissue growing in the colon that can become cancerous.

Inflammation

• Ulcerative colitis: ulcers of the colon and rectum.
• Diverticulitis: inflammation or infection of small pouches in the colon wall.

Functional disorders

• Irritable bowel syndrome: a condition causing abdominal cramping and other symptoms.

Tests used to study it

The colon and rectum are examined from the inside with a colonoscopy:

• EndoscopyProcedure

Keeping it healthy

• The NHS recommends about 30g of fibre a day with enough water: fluid helps waste move through the gut and softens stools, and without it constipation can follow.
• If cereals and grains cause bloating or IBS symptoms, get your fibre from fruit and vegetables instead, says the NHS.
• According to the CDC, quitting smoking lowers the risk of colorectal cancer, and the WHO lists it among the cancers linked to alcohol.