Nutrition and Human Digestive System

• The digestion process happens through the mouth, esophagus, stomach, small intestine, large intestine and anus. It also involves the liver, pancreas and gallbladder.
• Physical digestion is the mechanical breakdown of food into smaller pieces while chemical digestion is the decomposition of complex molecules into simple molecules.
• Foods entering the mouth are mixed with saliva and chewed.

  The saliva is produced by salivary glands. It forms bolus from the food to make it more easily swallowed. It contains salivary amylase which hydrolyses starch into maltose.
• Small Intestine - where most absorption occurs. Contains villi and microvilli. Villi increase surface area for absorption. Microvilli further increases surface area. Enzymes like trypsin, lipase, maltase, sucrase, lactase, and dipeptidase are present here.
• Stomach - churning and mixing of food with gastric juice containing HCl and proteolytic enzyme called pepsin. Pepsin breaks down protein into peptides.
• Liver - produces bile which emulsifies fats and neutralizes acidic chyme. Also stores glucose as glycogen and releases when needed. Produces urea from nitrogenous wastes.
• Pancreas - secretes pancreatic juice that contains enzymes such as amylase (starch), lipase (fat) and proteases (proteins).
• Gall Bladder - stores bile until needed. Bile helps break down fatty acids.
• Large Intestine - absorbs water and electrolytes from undigested material. Formation of fecal matter.
• The stomach lining contains 3 types of cells. Chief cells, parietal cells and mucous cells secretes pepsinogen, HCl and mucus respectively.
• Chief Cells secrete the digestive enzyme pepsinogen which is converted to active form pepsin by hydrochloric acid secreted by Parietal cells.
• Mucous cells secrete mucus to protect the stomach wall from HCl reactions and digestive enzymes.
• The food is churned in the stomach and turned into chymes before entering the duodenum.