Functions of the large bowel

There are five main functions of the colon:

1. Storage: the colon stores unabsorbed food residue. The longer the food residue stays in the colon the more water is absorbed, causing the stools produced to be harder.

2. Absorption: sodium, water, chloride, some vitamins and drugs, including steroids and aspirin, are absorbed from the ascending, transverse and descending colon. Approximately 1500ml of water enters the colon in a 24 hour period, which is reduced to 150-100ml by absorption in the colon. When the faecal matter enters the sigmoid colon it consists only of body waste, what we call ‘faeces’.

3. Secretion: mucus is secreted by the colon to lubricate the faeces.

4. Synthesis: bacterial colonisation in the colon produces a small amount of Vitamin K, thiamine, folic acid and riboflavin.

5. Elimination: peristaltic movement of faecal matter into the rectum, where its presence is detected by sensory nerve endings and a sensation of fullness is experienced, followed by a desire to defaecate.

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