Digestion

[Sonyfan08]

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The stomach has folds, the small intestine has folds and villi, while the large intestine has neither folds or villi. What is the significance of having folds? I know that stomach mainly functions to store food, the villi in small intestine is to increase surface area for re-absorption of materials, while the large intestine reabsorbs water...

 

[Sonyfan08]

Is the absorption of nutrients from the microvilli active? It says on mcat-review.org was active and is moving against the gradient. How so? Arent there more nutrient concentrated in the small intestine?

 

[MiCasaMD]

您读的

 

[fizzgig]

it's a surface area thing. the intestines need lots of surface area for exchange.

the gradient thing might relate to the microenvironment - yes there's lots of nutrients in the intestinal lumen, but the concentration that is right up on the brush border at any given time may not be enough to drive nutrients continuously across the border, and you want good continual absorption. so you have a lot of secondary active schtuff going on as i recall, where you build a gradient of one thing and use it to drag what you want where you want.