Food and Digestion

  • Created by: Harry
  • Created on: 16-05-14 12:24

Diagram of digestion


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An explanation of digestion (part 1)


  •  Chemical - Speeded up by enzymes => produced in tissues/glands in the gut, pass out of cells on to gut contents  => act on food


  • Mechanical - Physical breakdown => teeth biting and chewing food, cutting into smaller pieces that have a larger surface area

Muscles (intestine)

  • Circular layer => fibres running in rings around the gut
  • Longitudinal layer => fibres running down the gut
  • Both act to push food along the gut = waves of muscle contraction pass along the gut = Peristalsis
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An explanation of digestion (part 2)


  • Stomach wall secretes HCl => makes stomach contents highly acidic => kills bacteria that are taken into the gut along with food => helps us prevent food poisoning
  • Semi-digested food is held back in the stomach by a ring of muscle at outlet of stomach = sphincter muscle = when it relaxes, releases food into the first part of the small intestine = duodenum
  • Several digestive enzymes are added to the food in the duodenum, made by the pancreas = digest starch, proteins and lipids
  • Liver produces digestive juice = bile = stored in the gall bladder + passes down bile duct on to the food 
  • Bile turns any large liquid globules in food into an emulsion of tiny droplets = increases surface area so lipase enzymes can break it down more easily
  • Bile + pancreatic juice are also alkaline = neutralise the acidic content from the stomach before it moves on in the gut
  • Food passes along intestine + more enzymes are added until food has been broken into soluble end products 
  • Move on to the ileum of the small intestine
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An explanation of digestion (part 3)


  • Highly adapted for absorbing digested food = has a very large surface area = can efficiently absorb soluble products of digestion into the blood
  • Greates increase in surface area is due to tiny projections of the lining = Villi
  • Villi come in the millions = total area of lining thought to be about 300m2 = massive surface area
  • Villi have surface cells called Microvilli = extend surface area even more
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