The majority gastrointestinal reabsorption of water occurs in:
A. Small intestines
B. The esophagus
C. The colon
D. The stomach
Correct Answer: A. Small intestines
Approximately 85% to 95% of water absorption takes place in the small intestine. The colon absorbs only 500 to 100 cc. Approximately 9 liters of water travels to the gastrointestinal tract per day, and the small intestine absorbs 7 to 8 liters, while the colon absorbs the remaining 1 to 2 liters. Water absorption is thought to occur via osmotic gradients and aquaporins on intestinal membranes.
Option B: Absorption in the esophagus is virtually nil. The mucosa does contain mucous glands that are expressed as foodstuffs distend the esophagus, allowing mucus to be secreted and aid in lubrication. The body of the esophagus is bounded by physiologic sphincters known as the upper and lower esophageal sphincters.
Option C: By the time indigestible materials have reached the colon, most nutrients and up to 90% of the water have been absorbed by the small intestine. The role of the ascending colon is to absorb the remaining water and other key nutrients from the indigestible material, solidifying it to form a stool.
Option D: Contrary to popular thought, the stomach does not contribute to the absorption of any nutrients. This organ can be in the peritoneal cavity, located in the left upper abdominal quadrant, or in the epigastric abdominal region that acts to relay ingested food between the nervous system and the endocrine system.
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