What is Food absorption?

Generally, the passage of liquids into solid materials and of gases into liquids and solids. In terms of nutrition, absorption refers to the passage of substances into body fluids and tissues.
Digestion is only the first step in the assimilation of nutrients. This chemical breakdown of food particles releases AMINO ACIDS, GLUCOSE, FATTY ACIDS, VITAMINS, and MINERALS, which must then be absorbed by the intestine in order to be used by the body. Nutrients enter cells lining the intestine (the intestinal mucosa) and then are drawn into underlying cells, where they may enter either the lymph or bloodstream for distribution to tissues throughout the body. Tissues absorb nutrients from blood via capillaries, the smallest blood vessels. Gases, too, are absorbed. Blood becomes oxygenated in the lungs by absorbing oxygen from inhaled air and releasing carbon dioxide that was absorbed from tissues.
Absorption requires a disproportionately large surface area to meet the body’s needs. Consider the total area of the small intestine, which is a highly specialized absorptive organ. Though this tube is only about 20 feet long, it has a highly convoluted surface. Furthermore, the cells lining the surface, VILLI, are covered with microscopic, hairlike projections (MICROVILLI) that dramatically increase the absorptive area to a quarter the size of a football field. The microvilli move constantly, to trap nutrients and partially digested food, which is further digested. The upper regions of the small intestine, the lower DUODENUM, and upper ILEUM, are most active in absorbing nutrients. Other regions of the gastrointestinal tract carry out limited absorption:
The stomach absorbs some ALCOHOL, glucose, ions, and water, and the colon absorbs primarily water and minerals.