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