The Digestive System

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  • Digestive System
    • Many of the molecules in our food are polymers and so are insoluble (can't be absorbed directly by the bloodstream) so have to be catalysed by digestive enzymes
    • Organs
      • The Small Intestine: 2 main parts = duodenum and ileum. Chyme is moved along by peristalsis. In the dd. bile and pancreatic juice neutralise acidity of chyme and break into smaller molecules. In the ileum, the smaller molecules are then absorbed through the villi that line the gut wall.
      • The Stomach: Is a small sac with lots of folds allowing stomach to expand. Can hold up to 4 litres of food/liqid. Entrance and exit are controlled by sphincter muscles. Stomach walls produce gastric juice which helps break down food. Peristalsis of the stomach turns food into chyme.
      • Large Intestine: (colon) absorbs water, salts and minerals. Has folded wall for absorption. Bacteria decompose undigested nutrients.
      • Oesophagus: Tube that takes food from mouth to stomach using muscle contractions caled peristalsis. Mucus is secreted for lubrication.
      • Rectum: Faeces are stored here then pass through the sphincter muscles at the anus during defecation.
    • Pancreas: releases pancreatic juice (contains amylase, trypsin, chymotrypsin, lipase) into the duodenum through the pancreatic duct. Contain sodium hydrogencarbonate neutralises stomach acids.
    • Salivary Glands: 3 main pairs of salivary glands in the mouth. They secrete saliva (consists of mucus, mineral salts, salivary amylase).
      • Salivary Amylase breaks down starch into maltos.
    • Enzymes help us to digest food molecules
      • CARBO-HYDRASES catalyse the hydrolysis of carbohydrates
      • PROTEASES catalyse the hydrolysis of proteins


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