Biol 1 - Digestive System

Notes on the digestive system - Unit 1 of AQA AS Biology

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  • Created by: Stephanie
  • Created on: 10-05-12 19:36

Digestion

Digestion : The breaking down of large molecules into small molecules
                             OR
                   Polymers --> Monomers

Polymers are insoluble
So need to be hydrolysed into smaller molecules to be absorbed 

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Oesophagus

  • Uses waves of contractions to move food along called 'peristalsis'
  • Mucus is secreted from tissues in the walls for lubrication
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Stomach

  • Small sac with folds allowing expansion
  • Entrance and exit controlled by sphincters
  • Stomach walls secrete Gastric Juice; made of - HCL, Mucus and the precursor for pepsin
    -Pepsin (enzyme) hydrolyses breakdown of proteins and only works in acidic conditions (hence the HCL!)
  • Peristalsis of stomach churns food into 'Acid Chyme' 
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Small Intestine (The Duodenum & Ileum)

  • Acid chyme moved along by peristalsis
  • In Duodenum chyme is neutralized by bile and panreatic juice
    -which breaks it into smaller moleucules
  • In the Ileum small molecules are absorbed by villi in intestinal epithelium (gut wall) 
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Large Intestine (Colon)

  • Absorbs water, salts and minerals
  • Folded wall provides large surface area for absorption
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Rectum!

  • Faeces stored and passed through sphincter muslces
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Salivary Glands

  • Produce Saliva made of; salivary amylase, mucus and mineral salts
  • Salivary amylase (enzyme) breaks starch into maltose
  • Saliva also lubricates food
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Pancreas

  • Secretes pancreatic juice into Duodenum via pancreatic duct
  • Juice contains amylase and other digestive enzymes
  • Also contains sodium hydroxide which neutralises acidity of HCL from stomach acid
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