Tasks of enzymes in the stomach
The stomach contains mainly the digestive enzyme pepsin. It is produced by the main cells of the stomach mucosa in the form of the precursor pepsinogen. Only the acidic pH value in the gastric juice then leads to the conversion of the pepsinogen into pepsin.
This prevents the pepsin from already acting in the cells of the stomach lining and digesting the body itself. Pepsin splits proteins into peptides, i.e. shorter chains of amino acids. Only in the small intestine are the chains broken down into the actual amino acids.
Pepsin requires chloride as a cofactor. As one of the few enzymes of the digestive tract it can work in the acidic gastric juice. Many other enzymes need an alkaline environment to be able to work.
The enzymes gastric lipase, amylase and gelatinase also occur in small quantities in the stomach. The stomach lipase splits fatty acids from fats, the amylase maltose from starch and the gelatinase gelatin. Gelantine is animal collagen that is absorbed with meat or sweets containing gelatine, for example. It consists of proteins. Ultimately, therefore, amino acids are also released by the gelatinase.
Functions of enzymes in the blood
Blood is the so-called liquid organ. It is used to transport oxygen to the cells and carbon dioxide to the lungs. But other substances and molecules also use blood to move from one organ to the next.
Therefore, enzymes that are found in the blood have to be differentiated whether they are so-called plasma-specific (= blood-specific) enzymes or just “enzymes in transit”. Plasma-specific enzymes not only use the blood as a transport medium, but are actually used in the blood. These include enzymes involved in blood coagulation and enzymes of the fat and cholesterol metabolism.
One of the plasma-specific enzymes is lipoprotein lipase, which is located on the cell walls of blood vessels. Lipoproteins serve fatty acids as transport vehicles in the blood. In order for them to be reabsorbed into the cells, they must be released from the lipoproteins by the lipoprotein lipase. Lecithin-cholesterol acyltransferase is also involved in fat and cholesterol metabolism. It is attached to the outside of a certain type of lipoprotein and enables them to absorb free cholesterol from the blood.
Functions of enzymes in saliva
About 1 to 1.5 litres of saliva are produced daily. The smell or sight of food alone stimulates the production. As the first section of the gastrointestinal tract, the mouth is also involved in digestion.
Therefore, saliva already contains a digestive enzyme, amylase. A distinction is made between a so-called alpha- and a beta-amylase. Both break down polysaccharides into small glucose molecules.
A polysaccharide is composed of many individual sugar molecules. For example, the so-called starch from potatoes or bread is such a polysaccharide. It is broken down by amylase into maltose, which consists of two glucose molecules.
This first step in the digestion process is necessary so that the sugar molecules can later be better digested in the stomach and absorbed in the intestines. Starch is also a very good source of energy, because it contains a lot of energy for little weight. To make this advantage palatable to the brain, amylase splits the rather tasteless starch into sweet maltose, whereupon the brain asks for more. You can also try this effect at home: If you chew a piece of bread 20-30 times, after a certain time it starts to taste much sweeter than when you started. – Alpha-amylase and
- Alpha-glucosidase
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