Digestion and Absorption

• Digestion is the hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes.
• Fatty acids and monoglycerides are nonpolar molecules that can easily diffuse across the membrane of the epithelial cells.
• Enzymes involved in carbohydrate digestion include amylase in the mouth, maltase, sucrase, and lactase in the membrane of the small intestine.
• The products of carbohydrate digestive enzymes include amylase converting starch into smaller polysaccharides, maltase converting maltose into 2 x glucose, sucrase converting sucrose into glucose and fructose, and lactase converting lactose into glucose and galactose.
• Lipids are digested in the small intestine.
• Certain molecules are absorbed into the ileum despite a negative concentration gradient through co-transport.
• Exopeptidases break between specific amino acids at the end of a polypeptide.
• Endopeptidases break between specific amino acids in the middle of a polypeptide.
• Nutrients are then taken up into the cells along with Na + ions.
• Amino acids and monosaccharides require co-transport.
• Sodium ions (Na + ) are actively transported out of the cell into the lumen, creating a diffusion gradient.
• Lipase hydrolyses the ester bond between the monoglycerides and fatty acids.
• Dipeptidases break dipeptides into amino acids.
• Before lipids can be digested, they must be emulsified by bile salts produced by the liver, which breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area.