#17 Enzymes in the Human Body (English)

Food is an essential source of energy for humans. The nutrients that we take in everyday cannot be directly  absorbed and therefore need to be broken down. This is the part where enzymes play a very important rule in the digestion process.

From ingestion to egestion, enzymes break down large food molecules to smaller ones so that they can be absorbed.

1.     Amylase

--> In the mouth

Amylase in the mouth is in charge of breaking down starch into maltose.

•    Salivary gland secrets saliva that contains the enzyme amylase. While mastication (chewing) occurs, the tongue helps to mix the food with saliva so that amylase can collide with the starch molecules.

•   Starch is a long chain of carbon, hydrogen and oxygen. It is too big to be absorbed.

•   Amylase breaks it down into shorter chains, called maltose. 

--> In the small intestine

Further down in the digestive system, amylase breaks down maltose into even smaller molecules of glucose

•   Pancreas secretes pancreatic juice that contains amylase. The pancreatic juice goes through the pancreatic duct into the upper part of the small intestine (duodenum) where the last stage of digestion occurs.

•   Maltose is broken down into glucose, which is small enough to be absorbed.

2.  Pepsin

Pepsin is a type of protease that is in charge of breaking down large protein molecules into shorter chains of polypeptide.

--> In the stomach

•   Pepsin works the best in a low pH environment. This is why it works very efficiently in the gastric juice that contains hydrochloride acid in the stomach.

 •   Protein is a long chain of 20 different amino acids that are made of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur. It is broken down into shorter chains by pepsin.

 
•   Chains of polypeptide are not yet small enough to be absorbed. They still need to be broken down a bit further and this is done by the trypsin.

3.  Trypsin

Trypsin is another type of protease that is in charge of the further break down of polypeptide into amino acids.

--> In the small intestine

 

•   Trypsin is one of the three enzymes that are contained in the pancreatic juice secreted by the pancreas (the other two are amylase and lipase).

•   The pancreatic juice contains sodium hydrogencarbonate that neutralises the acidic gastric juice from the stomach because trypsin (as well as amylase and lipase) can be denatured in acid.

•   Trypsin breaks down chains of polypeptide into amino acids that are small enough to be absorbed. 

4.  Lipase

Lipase breaks down large fat molecules into absorbable glycerol and fatty acid.

--> In the small intestine

•   Lipase is contained in the pancreatic juice secreted by the pancreas.

•   Fat molecules in food are large and insoluble, which make these molecules very hard to be broken down. Fortunately, a substance called bile is produced in the liver and this substance emulsifies large insoluble fat molecules into tiny soluble droplets that can be more easily broken down.

•   Lipase can now break down the fat molecules into absorbable glycerol and fatty acid.