The food we eat has to be broken down into other substances that our bodies can use. This is called digestion. Without digestion, we could not absorb food into our bodies and use it.
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Human digestive system
Digestion happens in the digestive system, which begins at the mouth and ends at the anus.
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Human digestive system
After we swallow, our food passes through these organs in turn: oesophagus or gullet stomach ,small intestine, large intestine
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Stages of digestion
Different things happen to food as it passes through the digestive system: food is digested in the mouth stomach and small intestine ,digested food is absorbed into the bloodstream in the small intestine
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Stages of digestion
Excess water is absorbed back into the body in the large intestine, any undigested food passes out of the anus as faeces when we go to the toilet
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Liver and pancreas
The liver and the pancreas play an important part in digestion. The liver produces bile, which helps the digestion of lipids (fats and oil). The pancreas produces biological catalysts called digestive enzymes which speed up the digestive reactions.
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Digestion and enzymes
Our teeth break food down into small pieces when we chew. This is only a start to the process of digestion, as chewed pieces of food are still too large to be absorbed by the body.
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Digestion and enzymes
Food has to be broken down chemically into really small particles before it can be absorbed. Enzymes are the biological catalysts needed to make this happen quickly enough to be useful.
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Enzymes
Enzymes are not living things. They are just special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients:
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Enzymes
amylase and other carbohydrase enzymes break down starch into sugar ,protease enzymes break down proteins into amino acids, lipase enzymes break down lipids (fats and oils) into fatty acids and glycerol
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Carbohydrates
Carbohydrates are digested in the mouth, stomach and small intestine. Carbohydrase enzymes break down starch into sugars. The saliva in your mouth contains amylase, which is another starch digesting enzyme.
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Carbohydrates
If you chew a piece of bread for long enough, the starch it contains is digested to sugar, and it begins to taste sweet.
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Proteins
Proteins are digested in the stomach and small intestine. Protease enzymes break down proteins into amino acids. Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid.
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Proteins
This also kills harmful microorganisms that may be in the food.
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Lipids (fats and oils)
Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile, made in the liver. Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on. Bile is not an enzym
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Substances that are not digested
Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down, so they are not digested. Digestive enzymes cannot break down dietary fibre, which is why the body cannot absorb it.
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Other cards in this set
Card 2
Front
Human digestive system
Back
Digestion happens in the digestive system, which begins at the mouth and ends at the anus.
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