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Digestion enzymes are enzymes that break down polymeric macromolecules into their smaller building blocks. Digestive enzyme are found in the digestive tract of animals (including humans) where they aid in the digestion of food as well as inside cells, especially in their lysosomes. Enzymes are also found in the saliva, which is produced from within the salivary glands.

Digestion enzymes are classified by their substrates: proteases and peptidases split proteins into amino acids, lipases split fat into three fatty acids and glycerol, carbohydrases split carbohydrates such as starch into sugars, and nucleases split nucleic acids into nucleotides.

In the human digestive system, the main sites of digestion are the oral cavity, the stomach, the duodenum, and the jejunum and digestive enzymes are secreted by different glands: the salivary glands, the glands in the stomach, the pancreas, and the glands in the small intestine.

Contents

Oral cavity

Complex food substances taken by animals and humans must be broken down into simple, soluble and diffusible substances before they can be absorbed into the body. In the oral cavity, salivary glands secrete (or create) ptyalin. It is a type of α-amylase, which digests starch into small segments of multiple sugars and into the individual soluble sugars. Secreted by small and large salivary glands.

Salivary glands also secrete lysozyme, which kills bacteria but is not classified as a digestive enzyme.

Summary of the actions of digestive enzymes:

Stomach

The enzymes that get secreted in the stomach are called gastric enzymes. These are the following:

Small intestine

Pancreatic enzymes

The pancreas is the main digestive gland in our body. It secretes the enzymes:

  • Trypsin, is a protease that cleaves proteins at the basic amino acids.
  • Chymotrypsin, is a protease that cleaves proteins at the aromatic amino acids.
  • Steapsin, degrades triglycerides into fatty acids and glycerol.
  • Carboxypeptidase, is a protease that takes off the terminal acid group from a protein
  • 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, and glycogen, degrades most other carbohydrates. Humans lack the enzyme to digest the carbohydrate cellulose.
  • Pancreatic Secretion: Bile from the liver, which emulsifies fat, allowing more efficient use of lipase in the duodenum in converting lipids to smaller more manageable sizes. Bile is not considered an enzyme, but aids macronutrient degradation.

Proper small intestine enzymes

Four types of enzymes degrade disaccharides into monosaccharides:

The intestinal lipase 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.

References








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