Mechanical digestion of food
1. Segmentation of food occurs in the small intestine. Food mixes well with intestinal juices and mucus. Food moves equally everywhere from front to back.
2. Chyme moves slowly through the circulation by peristalsis.
3. Intestinal mucin mixes with food to lubricate it and move it from one place to another.
4. Mucus secreted by Brunner’s glands and goblet cells protects the small intestinal wall from enzyme action.
5. Bile reduces the action of bacteria and increases the speed of bile digestion.
6. The hormone cholecystokinin causes the gallbladder to contract. As a result, bile reaches the small intestine.
7. The brass emulsifies the lubricant into tiny particles like soap suds.
Chemical digestion of food
1. Protein digestion
(i) Amino peptidase enzyme breaks down polypeptides into amino acids.
(ii) Prolidase enzyme cleaves the peptide into proline.
(iii) Dipeptide and amino acids are produced from tripeptide under the action of tripeptidase enzyme.
(iv) Dipeptidase enzyme breaks down dipeptide into amino acids.
2. Carbohydrate digestion
(i) Amylase enzyme breaks down starch and dextin into maltose, maltotriose and minor dextin.
(ii) Maltose and glucose are produced from isomaltose under the action of isomaltase enzyme.
(iii) Maltotriase enzyme breaks down maltotriose into glucose.
(iv) Glucose is produced from maltose under the action of maltase enzyme.
(v) Sucrase enzyme breaks down sucrose into glucose and fructose.
(vi) Glucose and galactose are produced from lactose under the action of lactase enzyme.
3. Lipid digestion
(i) The enzyme lipase breaks down triglycerides and diglycerides into fatty acids, glycerol and monoglycerides.
(ii) Fatty acids and glycerol are produced from monoglycerides under the action of monoglyceridase enzyme.