How does Absorption Occur? The inside of the small intestine is made of a membrane that will allow molecules to pass through. To increase the absorbing surface, the intestine wall has many folds that contain projections, as pictured in the diagram.
Each of the many thousands of projections contains a network of structures that will accept the molecules and transport them away to other parts of the body. These structures include tiny blood vessels called capillaries and a tube called a lacteal.
Capillaries absorb amino acids, simple sugars, and water; they also absorb some fatty acids, vitamins, and minerals. Lacteals accept glycerol and the remaining fatty acids and vitamins.
The remaining food material continues its journey to the large intestine, most of which is called the colon. Absorption, mainly of water, continues in the first half of the colon, and the remaining material is transported on. Bacterial action converts the material into feces, which eventually reach the rectum, where they are stored until defecation occurs.