What are Digestive Enzymes?
Digestive enzymes are the chemical catalysts that break down food into simpler nutrients so that it can be absorbed. These enzymes make up a crucial part of the digestive process known as chemical digestion and acts along with mechanical digestion (chewing and churning) to allow for maximum absorption.
Digestive Enzyme Glands
The alimentary tract, also known as the gastrointestinal tract or gut, is structured in a manner that allows for optimal digestion and absorption of foods. Digestive enzymes are secreted from alimentary glands that lie in the lining of the gastrointestinal tract or may travel to the gut from external organs and glands like the liver, salivary glands and pancreas.
The alimentary tract is lined with specialized cells that lie on the surface or deep within pits and recesses, all of which play an important role in the secretory functions of the gut. Mucus is secreted throughout the tract and while this compound does not have any enzymatic activity, it does assist with lubrication needed for propelling the food through the gut. In addition, the mucus protects the lining of the gut from chemical digestion. In total the digestive juices (enzymes and mucus) secreted by the entire gastrointestinal tract (mouth to colon) is between 6 to 7 liters per day.
There are various factors which stimulate and inhibit the secretion of digestive enzymes, including the presence of certain types of foods, digestive hormones and nerve impulses (discussed under Stomach Nerves). Any disorder that affects the production, secretion and action of these enzymes or hormones will result in a number of digestive problems.
List of Digestive Enzymes from Organs
- Ptyalin containing alpha-amylase
- The salivary glands which includes the parotid, submandibular and sublinguals glands.
- Small glands in the lining of the mouth, known as the buccal glands, also play a role.
- Approximately 1 liter per day and includes mucus, various ions and lysozyme for antibacterial protection, the total secretion.
- Mucus but no digestive enzymes.
- Hydrochloric acid (HCL) – parietal cells
- Pepsinogen – chief cells
- Intrinsic factor – parietal cells
- Oxyntic glands
- Approximately 1.5 liters and includes mucus, water and ions from other stomach glands.
- Cholesterol esterase
- Refer to Pancreatic Enzymes for an explanation of each type of enzyme.
- Pancreas (exocrine)
- Approximately 1 liter including water and bicarbonate ions from the pancreas.
Liver and Gallbladder Secretions
- Bile itself is not an enzyme but bile acids have a detergent action which increases the surface area of fatty foods so that other digestives can act upon it.
- Approximately 1 liter per day including water and bicarbonate ions from the ducts.
Small Intestine Enzymes
- Enterocytes within the crypts of Lieberkuhn
- Approximately 2 liters and includes water, ions and mucus from the Brunner’s glands.
Large Intestine Secretions
- The large intestine also has crypts of Lieberkuhn but these glands only secrete mucus.
- Approximately 200 milliliters of mucus with bicarbonate ions and water.