Large intestine
Last part of the digestive system in tetrapods.
The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water and salts are absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation. Although it is shorter than the small intestine, it is called the large intestine because it is wider in diameter.
- length_in_humans
- about 1.5 metres (5 ft)
- proportion_of_gastrointestinal_tract
- about one-fifth
- rectum_length
- about 12 cm (4.7 in)
- water_arriving_daily
- about 1.5 litres
Lore & Background
The large intestine consists of the cecum (including the appendix), colon, rectum, and anal canal. The colon is the longest part, with sections including the ascending, transverse, descending, and sigmoid colon. The cecum is the first section and is involved in digestion, while the appendix is not involved in digestion and is considered part of gut-associated lymphoid tissue; its function is uncertain, but some sources believe it houses a sample of gut microbiota and can help repopulate the colon if depleted during an immune reaction. The ascending colon runs upward through the abdominal cavity for about eight inches (20 cm), and the transverse colon hangs off the stomach attached by the greater omentum.
Reader's Guide
The large intestine is significant as the terminal segment of the digestive system, responsible for absorbing water and salts and storing waste before defecation. In human medicine, the terms 'large intestine' and 'colon' are often used interchangeably, though most sources define the large intestine as the combination of cecum, colon, rectum, and anal canal. The colon does not play a major role in absorption of foods and nutrients, but about 1.5 litres of water arrive in the colon each day. The structure includes taeniae coli, haustra, and epiploic appendages. Arterial supply comes from branches of the superior and inferior mesenteric arteries, with venous drainage usually mirroring arterial supply. Lymphatic drainage varies by region. The diameters of colonic sections are important diagnostically, with thresholds for megacolon. The sigmoid colon is examined via sigmoidoscopy.
Did You Know?
- The large intestine is called 'large' because it is wider in diameter than the small intestine, though it is shorter.
- The cecum averages slightly less than 9 cm in diameter in healthy individuals, the widest part of the colon.
- The sigmoid colon is S-shaped and its walls contract to move stool into the rectum.
- The appendix has a high concentration of lymphatic cells and may help repopulate the colon with microbiota after an immune reaction.
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