Absorbed substances pass through the brush border into the capillary, usually by passive transport. Enzymes in the cells convert these disaccharides into monosaccharides that then leave the cell and enter the capillary. Lactose intolerance results from the genetic lack of the enzyme lactase produced by the intestinal cells. Peptide fragments and amino acids cross the epithelial cell membranes by active transport . Inside the cell they are broken into amino acids that then enter the capillary.
Gluten enteropathy is the inability to absorb gluten, a protein found in wheat.
Digested fats are not very soluble. Bile salts surround fats to form micelles that can pass into the epithelial cells. The bile salts return to the lumen to repeat the process. Bile salts are in turn absorbed in the ileum and are recycled by the liver and gall bladder. Fats pass from the epithelial cells to the small lymph vessel that also runs through the villus.