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Explain the digestion of food in the body?
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. Food has to be broken down chemically into really small particles before it can be absorbed. Enzymes are needed so that this break-down happens quickly enough to be useful.

The enzymes which take part in digestion are:

  1  carbohydrase or amylase enzymes break down starch into sugar

  2  protease enzymes break down proteins into amino acids

   3 lipase enzymes break down fats into fatty acids and glycerol.

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. If you chew a piece of bread for long enough, the starch it contains is digested to sugar, and it begins to taste sweet.

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. This also kills harmful micro-organisms that may be in the food.
Fats

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.
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 fibre, which is why it cannot be absorbed by the body.

These are the processes that happen in the digestive system:

ingestion (eating) ? digestion (breaking down) ? absorption ? egestion.

Absorption

Digested food molecules are absorbed in the small intestine. This means that they pass through the wall of the small intestine and into our bloodstream. Once in the bloodstream, the digested food molecules are carried around the body to where they are needed.

Only small, soluble substances can pass across the wall of the small intestine. Large insoluble substances cannot pass through.The inside wall of the small intestine needs to be thin, with a really big surface area. This allows absorption to happen quickly and efficiently. If the small intestine had a thick wall and a small surface area, a lot of digested food might pass out of the body before it had a chance to be absorbed.

To get a big surface area, the inside wall of the small intestine is lined with tiny villi (one of them is called a villus). These stick out and give a big surface area. They also contain blood capillaries to carry away the absorbed food molecules.

Egestion

Excess water is absorbed back into the body in the large intestine. What is left then is undigested food. This is stored in the rectum, the lower part of the large intestine, until we are ready to go to the toilet. It then comes out of the rectum through the anus as faeces. This process is called egestion.


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