Large intenstine diameter is larger than small intenstine?

Question

all content that is received by large intenstine is coming from small intenstine.large intenstine doesnt secreate anything,and it absorb water so the content it has to keep is reduced in volume than in the small intenstine.then why i lumen larger in the 1st one.is it that small intenstine is longer.hense it s volume is larger?

Answer 1

It needs more surface area.  A longer skinnier tube will will more surface area than a fat shorter tube.

Answer 2

Yep--what the PP said.  You need a ton of surface area to extract all the nutrients from what you eat, and if the lumen of the small intestine was bigger, not only would it be harder for the villi that line it to be in contact with the food, it wouldn't be able to be all packed into the abdomen in all those loops and coils.  The large intestine is also very linear compared to the small intestine--it doesn't need to be as long either.

The large intestine is...how shall I put this delicately?...also responsible for a certain amount of storage of waste products, at least until such time as is convenient to expel them.  You wouldn't want too small a lumen or things would get stuck too easily, and it would get distended and painful very quickly.