Absorption is the process of transfer of substances from the surface tissues and from the cavity organs in the blood and lymph. This may be due to osmosis, diffusion, and in the intestines due to special pumping function villous apparatus. In the digestive tract absorption of water, salts, nutritional and medicinal substances occurs primarily in the small intestines. For intestinal epithelium size of pores can pass through the molecule of the substances does not exceed 4 A. Absorption depends on the charge of an ion. Multiply charged ions are absorbed poorly.
Nutrients can be absorbed into the blood and lymph only after enzymatic digestion in the stomach and intestines (see Digestion). Carbohydrates are absorbed in the form of simple sugars; products of digestion of proteins in the form of amino acids, fats - in the form of fatty acids, glycerin, and cholesterol. The latter comes from the intestine directly to the lymph. Fats in the intestine are split using lipase on fatty acids and mono - and diglycerides; passing through the epithelial layer of the intestine, they partially exposed resynthesis in neutral fat. The absorption of neutral fat occurs mainly in the lymph. Motor function of the villi are regulated by the hormone - wilikinson formed in the mucosa of the duodenum and exciting movement of the villi. The function of cilia and on absorption function of cells of the intestinal mucosa regulating influence of the hormones of the pituitary gland and the adrenal cortex, and the sympathetic and parasympathetic nervous system, the thalamus and cerebral cortex.