The principal function of the intestinal tract is to absorb water, electrolytes and nutrients from food. The quantity of water that reaches the colon in 24 h is about 9 L (Fig. 1). About 150 mL of this is found in the feces; 99% is absorbed, most by the jejunum, less by the ileum and about 15% by the colon (Binder 1989). Only a small volume (2 L) of this liquid is swallowed during the day, while most of it (7 L) is secreted throughout the digestive tract: saliva, 1.5 L; gastric juice, 2.5 L; bile, 0.5 L; pancreatic juice, 1.5 L; intestinal juice, 1.0 L). This liquid lubricates the stomach and intestine and eases the movement of the chyme through the gastrointestinal tract. The fluid also helps to remove residual food left in the intestinal passages (a washing function) and thus keeps bacteriological flora at physiological levels. Moreover, these secretions facilitate the movement of immunoglobulins from the crypts to sites more exposed to the lumen. When the absorption of fluid is excessive or when physiologic secretion is impaired, the feces become dehydrated and transit through the bowel may be slowed. On the other hand, when laxatives are given orally, fluid accumulates in the intestinal lumen, the rate of transit is increased and defecation is facilitated.
KeywordsIrritable Bowel Syndrome Vasoactive Intestinal Peptide Platelet Activate Factor Vasoactive Intestinal Polypeptide Crypt Cell
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