The Alimentary Canal: The Large Intestine

1. Mouth
2. Oesophagus
3. Stomach
4. Small intestine
5. Liver
6. Pancreas
7. Large intestine

7. The Large Intestine

• Although large in diameter, the large intestine is just 1.5m long.
• The function of the large intestine is to re-absorb water. This happens in the colon.
• The appendix and caecum are vestigial organs**.** They were needed for digestion of raw meat and roughage but humans no longer need them.
• They were once important for digesting raw meat and roughage but are no longer essential in humans.
• Faeces is stored in the rectum and egested through the anus.
• Diarrhoea: Occurs when unabsorbed material moves too quickly through the colon, leaving less time for water reabsorption.
• Constipation: Occurs when unabsorbed material moves too slowly through the colon. Too much water is reabsorbed so the faeces are more solid.

Role of Fibre

• Fibre stimulates peristalsis and reduces the risk of constipation.
• Fibre absorbs and stores water.
• This causes the unabsorbed waste to expand.
• The bulk of the waste stimulates the muscles of the intestine to work, and in this way stimulates peristalsis.

Symbiotic Bacteria in the Intestines

• The transverse colon contains trillions of bacteria.
• These bacteria benefit humans in two main ways:
  1. Producing vitamins: including vitamins B and K.
  2. Feeding on waste: assisting in digestion.
• In return, humans provide bacteria with: 3. A place to live. 4. A food supply.
• This relationship is mutualistic, as both organisms benefit.