• Physical digestion: A process that involves mechanical action such as chewing action and peristalsis to break up large pieces of food into small pieces to increase the surface area for the action of digestive enzymes.

  
  

• Chemical digestion: The breaking down of complex molecules into simpler molecules to enable the molecules to be transported into body cells. The process involves a hydrolysis reaction catalyzed by digestive enzymes.

The presence of food in the mouth triggers the salivary glands; parotid gland, sublingual gland, and submandibular gland to secrete salivary amylase that digests starch into maltose

• Mucous cell: Produces mucus to protect the stomach wall from being eroded due to the action of hydrochloric acid.

• Parietal cell: Secretes hydrochloric acid to destroy bacteria and provides an acid medium for pepsin to function optimally.

• Chief cell: Secretes pepsinogen which is later converted into pepsin in the presence of hydrochloric acid to digest protein into the polypeptide.

• Liver: Produces bile which is stored in the gallbladder.

• Gallbladder: Secretes bile which is channeled to the duodenum by a bile duct.

• Duodenum:

  • Pancreatic amylase hydrolyzes starch into maltose

  • Lipase hydrolyzes lipids into fatty acids and glycerol

  • Trypsin hydrolyzes polypeptides into shorter peptides

• Pancreas: Secretes pancreatic amylase, trypsin, and lipase which is channeled to the duodenum by a pancreatic duct.

• Small intestine:

  • Maltase hydrolyzes maltose into glucose.

  • Lactase hydrolyzes lactose into glucose and galactose.

  • Sucrase hydrolyzes sucrose into glucose and fructose.

  • Erepsin hydrolyzes peptides into amino acids