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Mariah's avatar

Approximately what percentage of water absorption takes place in the small intestine vs. the colon (and a followup question)?

Asked by Mariah (19100 points ) August 21st, 2011

High school biology classes always taught me that the colon does the majority of the water absorption, but I read recently that as much as 90% of water absorption occurs in the small intestine. Anyone know what the correct figures are on this?

And if so much water absorption occurs in the small intestine, why do diseases that only affect the colon, such as ulcerative colitis, often have as a symptom very watery diarrhea?

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2 Answers

Lightlyseared's avatar

The gi tract requires chyme to be pretty liquid in order to be able to move it around through peristalsis. So even though the small bowel does absorb a lot of water from the chyme it is not until the colon that it starts to become solid. In fact the rectum and left colon are much more muscular than the right colon just to deal with the more solid stool.

CWOTUS's avatar

Here is a website (from Colorado State University – the first one I happened to click into) that shows that the figure is 80%. Apparently your high school biology text was incorrect.

And I learned new words today: chyme (and chymus) and ingesta. Oh, happy day!

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