Digestive Enzymes

Digestive enzymes are enzymes in the digestive system that break down food so that the body can absorb it. They are secreted by different glands: the salivary glands, the glands in the stomach, the pancreas, and the glands in the small intestines.
In the mouth, salivary glands secrete ptyalin. It is an alpha-amylase, which digests starch into small segments of multiple sugars and into the individual soluble sugars.
The enzymes that get secreted in the stomach are called gastric enzymes. These are the following:
Pepsin is the main gastric enzyme. As it breaks proteins into smaller peptide fragments, it is a peptidase.
Gelatinase, degrades type I and type V gelatin and type IV and V collagen, which are proteoglycans in meat.
Gastric amylase degrades starch, but is of minor significance.
Gastric lipase is a tributyrase by its biochemical activity, as it acts almost exclusively on tributyrin, a butter fat enzyme.
The pancreas is the main digestive gland in our body. It secretes the enzymes:
Trypsin, is a peptidase, that breaks down peptides in the small intestine.
Chymotrypsin, also a peptidase
Steapsin, degrades triglycerides into fatty acids and glycerol.
Carboxypeptidase, splits peptide fragments into individual amino acids. It is a protease.
Several elastases that degrade the protein elastin and some other proteins.
Several nucleases that degrade nucleic acids, like DNAase and RNAase
Pancreatic amylase that, besides starch, glycogen and cellulose, degrades most other carbohydrates.
Bile from the liver, which emulsifies fat, allowing more efficient use of lipases in the duodenum; in converting lipids to their component fatty acid and glycerol molecules
Lower in the small intestine are secreted several peptidases.
The jejunum and ileum secretes a juice called succus entericus which contains the following: Six types of enzymes degrade disaccharides into monosaccharides:
Sucrase, which breaks down sucrose into glucose and fructose
Maltase, which breaks down maltose into glucose.
Isomaltase, which breaks down maltose and isomaltose
Lactase, which breaks down lactose into glucose and galactose (tends to be low in adults)
Intestinal lipase, which breaks down fatty acids.
The small intestine receives lipase, trypsin and amylase from the pancreas. They are transported from the pancreas to the duodenum through the pancreatic duct. Protein, fats and starch are broken down into smaller molecules. However, they are not fully broken down yet. This causes the enzymes of the small intestine to act upon them. These enzymes include peptidase, which breaks down peptides into amino acids and the enzyme maltase acts upon maltose which produces glucose. These molecules are absorbed by the villi in the small intestine and according to the molecule they are either absorbed by the lacteal or blood capillaries.
This is the normal course of events in the digestive tract of humans. However, as you can see, there are a lot of enzymes involved in the process; lack of any of them may impede digestion. This becomes more likely as you get older. Digestive enzymes supplements simply fill in the most common gaps in the process.