Year 11 Biology Digestion 3
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Describe the action of digestive enzymes:
The role of digestive enzymes is to act upon food being eaten and break it down multiple times, until it is small enough to be absorbed into the bloodstream through the villi in the small intestine. The enzymes are released by the pancreas, and different enzymes act on different nutrients to digest.
Why does the small intestine have a large blood supply?
Since nutrients are absorbed through the bloodstream, the more blood in the small intestine, the more nutrients that can be absorbed.
What is absorbed into the blood stream?
Nutrients such as glucose, amino acids, some fatty acids and glycerol are absorbed into the bloodstream through the capillaries in the villi.
What are lacteals?
- - Lacteals are blind extensions of the lymphatic system.
- - Transports glycerol and fatty acids to the veins near the neck to be absorbed into the bloodstream.
Describe the path of the blood after it leaves the small intestine.
The villi absorb the nutrients into the lacteals. These lymph vessels transport the blood, along with glycerol and fatty acids, to the neck veins to be absorbed back into the bloodstream.
What is the function of the jejunum and ileum?
- - Continue digesting food.
- - Cells of the jejunum and ileum secrete aminopeptidases, which complete protein digestion.
- - Cells also secrete enzymes that act on specific carbohydrates, which complete the digestion of disaccharides.
Descibe the structure of the small intestine.
- - The wall lining is made of folds instead of being flat; this increases the SA/V ratio.
- - Each fold is covered in finger-like projections called villi.
- - Each villi is covered in microvilli, this further increases the SA/V ratio of the small intestine.
What process allows the products of digestion to pass through the gut lining, and where do they go?
- -They are absorbed through the cells lining the gut by diffusion.
- - The absorbed products pass through the gut lining and into the lymph and blood vessels below the epithelial cells of the small intestine.
- - Active transport also occurs. The cells absorbing the products must expend energy to absorb the material against a concentration gradient.
What do the capillaries in the villi do?
They transport amino acids and monosaccharides to the liver via the hepatic portal vein.
How much of the total nutrient absorption takes place in the small intestine, and where does the rest occur?
- - Approximately 90% of the absorption of nutrients takes place in the small intestine.
- - The other 10% occurs in the stomach and large intestine.
How much water enters the intestines a day? Describe where they enter from.
- - 2300 mL enters the alimentary canal after being obtained from food and fluids.
- - 7000 mL enters the canal as enzymes and mucus are secreted by the canal wall cells.
- - 9000 mL is absorbed a day, 8500 mL of this is absorbed along with the products of digestion in the small intestine.
What is the cause of diarrhoea?
If the water is not absorbed properly, the continued loss of water dehydrates the body, and causes the faeces to become watery.
By what method is water absorbed by the intestine? How much is left for the large intestine after this has occurred?
- - Osmosis allows water to be absorbed by the cells of the small intestine.
- - After osmosis has occurred, approximately 500 mL of water remains for the large intestine.
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