DIGESTION REVISION BLOCKS. MECHANICAL & CHEMICAL DIGESTION. PERISTALSIS. As food is broken down, it needs to be transported through each part of the digestive system.
As food is broken down, it needs to be transported through each part of the digestive system.
To get from the mouth to the stomach, the food has to travel down the oesophagus. It is not gravity that pulls the food down, it is waves of peristalsis. Peristalsis is the contraction and relaxation of circular muscles in the wall of the gullet.
Peristalsis is also used in the stomach to break up the chunks of food into a mush as part of mechanical digestion.
There are two types of digestion: mechanical and chemical.
Mechanical digestion is when food is ground up using the teeth. Another example of mechanical digestion is when the food is churned by the movements in the alimentary canal.
Chemical digestion is the breaking down of food using enzymes. Enzymes break large food molecules into smaller ones.
The point of digestion is to break down large, insoluble food molecules into smaller, soluble ones that can be easily absorbed into the bloodstream. Enzymeshelp to do this. There are different types of enzymes which each break down different food substances.
Carbohydrates are broken down by the enzyme carbohydrase. It is found in saliva in the mouth and in the pancreatic juice that is poured into the small intestine from the pancreas. It breaks down starch molecules into glucose molecules.
Proteins are broken down by the enzyme, protease. This is found in the pancreatic juice and also in gastric juice which is found in the stomach. This enzyme breaks protein molecules into amino acid molecules.
Fats and oils, or lipids, are broken down by the enzyme lipase. This is found in the pancreatic juice. Lipase breaks fat molecules into fatty acid and glycerol molecules.
The juices that are found in the digestive system contain enzymes to break down food molecules. However, different enzymes work more efficiently when they are at their different optimum pHs.
In the gastric juice found in the stomach, there is an enzyme called protease. The juice also contains hydrochloric acid to kill bacteria and to make the juice acidic; the optimum pH for protease.
The enzymes that break down the food in the small intestine, however, work more efficiently in an alkaline. Therefore, a juice called bile is added. It is made by the liver and is stored in the gall bladder. It also emulsifies fats.
Food that cannot be digested is passed into the large intestine.
The first part of the large intestine is the called the colon. This is where the water in the large intestine is absorbed back into the blood, making the remaining food in the large intestine into semi solid faeces.
This is stored in the part of the large intestine called the rectum.
Finally, the faeces are passed out of the body altogether through the last part of the digestive system: the anus.
Small intestine (ileum)
Small intestine (duodenum)
Carbohydrates and proteins
VITAMINS + SALTS
FATS + OILS
Glucose and simple sugars
Glycerol and fatty acids
Keeping the body in good health
Many uses in the body
Excess broken down in liver
Excess stored in liver as glycogen
Energy produced in cell respiration
Stored under the skin
Form proteins in the body
Passed to the kidneys by blood for removal as urine
Some out in sweat