Intestinals

Intestinals are the best way for organisms for increasing the contact surface, so things like absorbtion will go faster.
Increasement of contact surfaces by intestinals occur often in a body: think about the pulmonary alveoluses in the lungs, the mitochondrion ...

Because this is so important to survive, the intestinal occur on different levels: on cell-mediated, on microscopic and on the normal level.

This applied on the small intestine.
When we cut the small intestine, we immediately see that the inner wall of the small intestine wrinkles. These are called the intestinal valleculas.

When we look to it at microscopic level, we see that these intestinal valleculas are wrinkled again: they are called intestinal villi.

At cell-mediated level every cell is wrinkled again: these are the microvilli.