Which GI organ absorbs the majority of ingested water? Source needed.
March 13, 2012 4:18 PM   Subscribe

Which GI organ absorbs the majority of ingested water? Source needed.

A doctor today told us that the stomach was the organ that absorbed the majority of ingested water. I thought it was the colon.

She provided an article from 1965 to back up her statement.

From my search now, it seems that we were both wrong - that it is the small intestine. But I'd like a published article to back this up, if it's true. And something more recent than 1965.

I'm not that great at PubMed searches. Any help?
posted by 254blocks to Science & Nature (7 answers total) 3 users marked this as a favorite
I'd recommend looking in a recent physiology textbook for this one over a medical journal.

Sorry - that's not really an answer!
posted by lulu68 at 4:40 PM on March 13, 2012 [1 favorite]

Response by poster: I agree, but I don't have access to one ... I wonder if there's one online? Plus, I thought that maybe someone who had access to a recent physiology textbook could find the answer, then the reference for that answer, and give me *that*. :D
posted by 254blocks at 4:42 PM on March 13, 2012

Response by poster: The answer within said textbook, I meant.
posted by 254blocks at 4:42 PM on March 13, 2012

Back when I took my wEMT course they definitely said that the small intestine was where most water absorption happens. The colon will do it too but most of the work is done by the small intestine I believe. The stomach doesn't really absorb anything, it's lined with mucous to prevent the contents (which of course includes some nasty acids) from touching your actual tissues. Your small intestine is your body's primary interface for absorbing material from the outside (food and water) and incorporating it.
posted by Scientist at 4:46 PM on March 13, 2012

Best answer: Looking at my Human Physiology book now 6th Ed. by Sherwood states that both the small and large intestine absorb water as shown on the chart on pg. 582.

Also, on pg. 613 it states" All products of carbohydrate, protein, and fat digestion, as well as most of the ingested electrolytes, vitamins, and water, are normally absorbed by the small intestine indiscriminately." There is a section on pg. 615-616 tilted 'Energy-dependent Na+ Absorption Drives Passive H20 Absorption,' which states" the absorption of Cl-, H20, glucose, and amino acids from the small intestine is linked to this energy-dependent Na+ absorption."

The large intestine or colon continues to "extract more H20 and salt from the contests" and whose primary function is to store feces before defecation (623). The colon doesn't absorb as much as the small intestine because it has less absorptive surface area. There is a section titled 'The Large Intestine Absorbs Salt and Water, Converting the Luminal Contents into Feces.' on pg 626. "The colon normally absorbs salt and H20. ... Of the 500 ml of material entering the colon per day from the small intestine, the colon normally absorbs about 350 ml, leaving 150 g of feces to be eliminated from the body each day. This fecal material normally consists of 100 g of H20 and 50 g of solid, including undigested cellulose, bilirubin, bacteria, and small amounts of salt" (626)
posted by Mr. Papagiorgio at 5:00 PM on March 13, 2012

From the eTextbooks available to me through my university's medical library, the small intestine appears to be the answer by a large margin. It is probably worth noting that the majority of the water that the GI system handles daily does not come from diet, but instead comes from mucosal secretions that are then reabsorbed back through the small intestine. Perhaps the difference in your sources is based on some sort of technicality.

Regardless, if we are talking about net flow, there is a figure in my book (titled Gastrointestinal Physiology) that makes this pretty clear (I would love to post the image but suspect it would be a copyright violation). To summarize, the average adult's GI tract is presented with ~9L of water per day, 2L of which is from dietary intake. Saliva, gastric juices, pancreatic juices, etc. contribute another 7L. The small intestine absorbs 7L of the total intake (78%, it says), while the colon absorbs 1.9L (21%). The stool contains that final 1% of water.

Source: Barrett KE. Chapter 5. Water and Electrolyte Absorption and Secretion. In: Barrett KE, ed. Gastrointestinal Physiology. New York: McGraw-Hill; 2006. http://www.accessmedicine.com/content.aspx?aID=2307040. Accessed March 13, 2012.
posted by wondercow at 5:57 PM on March 13, 2012 [1 favorite]

Now I'm interested in the 1965 article. What was the title?
posted by Lt. Bunny Wigglesworth at 6:47 PM on March 13, 2012 [1 favorite]

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