Digestive system

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  • Digestive system
    • Oesophagus
      •  The tube that takes food from the mouth to the stomach 
        • using waves of muscle contractions called peristalsis; the muscle layer is thick to help with this
      • Mucus is secreted from tissues in the walls, to lubricate the food’s passage downwards
    • Stomach
      • A small sac with many folds which allow it to expand
      • The entrance and exit are controlled by the sphincter muscles
      • The gastric juice produced here help digest food
        • It consists of hydrochloric acid, pepsin, and mucus
          • Pepsin hydrolyses proteins into smaller polypeptide chains and only works in acidic conditions
          • The mucus protects the stomach from acid damage and pepsin
      • Peristalsis of the stomach churns the food in a fluid called chyme
    • Small intestine
      • Chyme is moved along it by peristalsis
      • 2 main parts
        • duodenum
          • bile (an alkali) and pancreatic juice neutralises the chyme and breaks it down
            • Bile emulsifies lipids in the food
              • It breaks up large globules into smaller globules = increases surface area
                • Lipase digestion more efficient
        • ileum
          • Small, soluble molecules are absorbed
            • villi in the gut wall by diffusion, facilitated diffusion and active transport
              • villi + microvilli increase surface area so that soluble molecules are absorbed quickly

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