The large intestine is mainly devoted to activities like water and Vitamin K absorption, and the rectum acts as a transient storage place for feces prior to their elimination through the anus.
It is not enough for organisms to simply digest food. They must also be able to transport this food to their cells in a form in which it can be utilized for energy. Absorption is the process by which water and other nutrients pass through membranes to cells. Most absorption of nutrients occurs in the small intestine. The most important absorbing agents located here are the villi. These microscopic outpocketings of the lining of the surface of the small intestine significantly increase its absorptive surface. Villi contain capillaries and lacteals (projections of the lymphatic system). They are also covered with microvilli, that further increase surface area and aid in absorption.
Amino acids, small fatty acids, and glucose pass through the villi walls into the capillary system. Some nutrients, such as glucose and amino acids, are actively absorbed (transported into cells using energy), while others are passively absorbed. More than 20 feet of intestine provide a large surface area for absorption.
This animation (Audio - Important) describes the structure of the small intestine.
This animation (Audio - Important) describes the process of absorption.