digestion and absorption

• Digestion is the hydrolysis of large, insoluble molecules, into small soluble ones that can be absorbed across cell membranes.
• The enzymes involved in carbohydrate digestion are amylase, sucrase, maltase, and lactase.
• Amylase converts starch into glucose and maltose.
• Sucrase converts sucrose into fructose and glucose.
• Lactase converts lactose into galactose and glucose.
• Lipids are digested in the small intestine.
• Before lipids can be digested, they must be emulsified by bile salts, that are produced in the liver. This breaks down the lipids into smaller, more soluble molecules called micelles, which increases surface area.
• Lipids are digested by the hydrolysis of ester bonds between monoglycerides and fatty acids.
• The enzymes involved in protein digestion are endopeptidases, exopeptidases, and dipeptidases.
• Endopeptidases break peptide bonds between specific amino acids in the middle of a polypeptide.
• Exopeptidases break peptide bonds between specific amino acids at the end of a polypeptide.
• Dipeptidases break dipeptides into amino acids.
• Molecules are absorbed into the ileum by co-transport.
• Amino acids and glucose are transported by co-transport.
• In co-transport, sodium ions are actively transported out of the cell into the lumen, creating a diffusion gradient. Nutrients are then taken up into the cells along with sodium ions.
• Fatty acids and monoglycerides do not require co-transport, as they are non-polar, and so they can diffuse easily across the membrane of the epithelial cells.