Water Absorption

[maikelm]

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Where does water absorption happen primarily? Is it the large or small intestine? I've always thought it was the large intestine, and that's how I was taught.

 

[yeasureyoubetcha]

Where does water absorption happen primarily? Is it the large or small intestine? I've always thought it was the large intestine, and that's how I was taught.

It's all over. By the time contents reach the large intestine most contents have been absorbed so all that's left is water and some ions, then whatever is being excreted. Don't forget the kidney plays a major role in water reabsorption though


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[maikelm]

It's all over. By the time contents reach the large intestine most contents have been absorbed so all that's left is water and some ions, then whatever is being excreted. Don't forget the kidney plays a major role in water reabsorption though


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Would there be some cotransporters in the small intestine that could transport water to the bloodstream? Even a small amount? Maybe the osmotic gradient made by "pulling" most ions?

 

[yeasureyoubetcha]

Would there be some cotransporters in the small intestine that could transport water to the bloodstream? Even a small amount? Maybe the osmotic gradient made by "pulling" most ions?

There's an osmotic gradient for water. Transport happens thru aquaporins. No cotransport. Intestinal cells also interdigitate with each other on their lateral surfaces. This increases surface area for distention. Sodium is pumped out into the lateral interstitial space within the interdigitations and water follows. The increased pressure in this space distends the sides forcing fluid down into the lamina propria of the gut tube where it gets picked up by the vasculature.


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