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Digestive Enzymes

Complex foods must be broken down into simple, soluble, and diffusible substances before they can be absorbed. Digestive enzymes are substances that help break down food so that it can be absorbed by the body. They are found in the digestive tract as well as inside of cells. Most enzymes are secreted by the salivary glands in the mouth, secretory cells in the pancreas, secretory cells in the stomach, and secretory glands in the small intestine.


Types of Digestive Enzymes

  • Proteases and peptidases split proteins into amino acids.
  • Lipases split fat into three fatty acids and a glycerol molecule.
  • Carbohydrases split carbohydrates such as sugar and starch into simple sugars such as glucose.
  • Nucleases split nucleic acids into nucleotides.

Digestive Enzymes in the Mouth

There are two salivary glands in the mouth that secrete digestive enzymes:
1. Mixed glands: these glands contain mucous and serous cells. Their secretion is mucinous and thick.
2. Serous Glands: these glands produce a secretion rich in enzymes, water, and electrolytes.

The following enzymes and substances are released by the mixed and serous glands in the mouth. As you will see, it is very important to chew your food thoroughly to aid digestion and preserve the health of the digestive system:
  • Amylase (Ptyalin) - Carbohydrate digestion begins in the mouth with Amylase as it breaks down complex carbohydrates into simple sugars and smaller chain carbohydrates.
  • Haptocorrin (R-factor) - Though released in the mouth, haptocorrin binds to vitamin B12 in the stomach to protect it from the acids there. In the duodenum the haptocorrin is separated from the B12 so it can the bind to intrinsic factor and be absorbed in the terminal ileum by cubam receptors.
  • IgA - IgA are actual antibodies produced by the body that the digestive system uses against bacteria and viruses. Any bacteria or viruses coated with IgA are attacked by white blood cells.
  • Lingual lipase - Lipid and fat digestion begins in the mouth with the release of lingual lipase.
  • Lysozyme - Lysozyme acts as an antiseptic.
  • Mucin - The purpose of mucin is to make food movement through the esophagus easier by lubricating it.
  • Potassium bicarbonate - Bicarbonate prevents acid from damaging the lining of the esophagus, neutralizes acidity to preserve the teeth, and neutralizes bacteria toxins.

Gastric Enzymes

Gastric enzymes are enzymes that are secreted in the stomach. There are four types of cells in the stomach:
  • G Cells - G Cells produce gastrin which is a hormone which in turn causes the parietal cells to excrete. It does this in response to food entering the stomach.
  • Gastric chief cells - These cells produce pepsinogen which is the primary gastric enzyme that, when mixed with stomach acid, turns into its active form, pepsin. Pepsin breaks down proteins into amino acids and peptide fragments.
  • Goblet cells - Goblet cells secrete bicarbonate and mucin to protect the stomach lining from irritants and acids.
  • Parietal cells - Parietal Cells produce hydrochloric acid and intrinsic factor. Hydrochloric acid is the stomach acid which turns pepsinogen into pepsin, helps break down proteins, and kills bacteria and viruses.

    Intrinsic factor binds Vitamin B12 in the duodenum, creating a Vit. B12-IF complex. This is then absorbed in the terminal ileum by cubam receptors.

Pancreatic Enzymes

The pancreas releases enzymes via the pancreatic duct into the duodenum. It contains the following enzymes:
  • Several elastases that degrade the protein elastin and some other proteins.
  • Pancreatic lipase that degrades triglycerides into fatty acids and glycerol.
  • Cholesterol esterase
  • Phospholipase
  • Several nucleases that degrade nucleic acids, like DNAase and RNAase
  • Pancreatic amylase that breaks down, besides starch and glycogen, most other carbohydrates.
  • Trypsinogen - Trypsinogen is activated by enterokinase in the duodenum and turns into Trypsin. As Trypsin, it helps break down proteins at the basic amino acid level.
  • Chymotrypsinogen - Chymotrypsinogen is activated in the duodenum and helps break down proteins at their aromatic amino acids.
  • Carboxypeptidase - Carboxypeptidase is a protease that takes off the terminal amino acid group from a protein

Duodenum Enzymes

The following enzymes and hormones are produced or activated in the duodenum:
  • Secretin - Secreting is an endocrine hormone produced by the duodenal "S cells" in response to high acidity of the stomach contents.
  • Cholecystokinin (CCK) - Cholecystokinin's role is to increase secretion of acinar cells and increase production of pancreatic juice. CCK also increases gallbladder contraction, causing release of pre-stored bile into the cystic duct, and eventually into the common bile duct and via the ampulla of Vater into the second anatomic position of the duodenum. CCK also decreases the tone of the sphincter of Oddi, which is the sphincter that regulates flow through the Ampula of Vater. CCK also decreases gastric activity and decreases gastric emptying, thereby giving more time to the pancreatic juices to neutralize the acidity of the gastric chyme.
  • Gastric inhibitory peptide (GIP) - GIP decreases gastric motility and is produced by duodenal mucosal cells.
  • Motilin - Motilin increases gastrointestinal motility via specialized receptors called "motilin receptors."
  • Somatostatin - Somatostatin is a hormone that is produced by duodenal mucosa and also by the delta cells of the pancreas. Its main function is to inhibit a variety of secretory mechanisms.
  • Sucrase - located throughout the small intestine
  • Lactase - Lactase is a significant brush border enzyme in that a majority of Middleastern and Asian population lack this enzyme and also this enzyme decreases with age, and as such lactose intolerance is often a common abdominal complaint in the Middleastern, Asian, and older population, manifesting with bloating, abdominal pain, and osmotic diarrhea.
  • Maltase - located throughout the small intestine

Digestive Enzyme Supplements

Research is ongoing and this area will be updated.

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