Digestive Enzymes: Definition, Types and Functions

Digestive enzymes can be defined as a group of enzymes that cause the breakdown of polymeric macromolecules (food molecules) into smaller components that our digestive system can absorb.

• Digestive enzymes are present in the organs of humans like gall bladder, stomach, pancreas, liver, and even in saliva.
• Our body is incapable of digesting food, therefore enzymes are present to make the process easier.
• Amylase, lipase, sucrase, and hydrolase are some of the digestive proteins found in the body.

In this article, we will discuss the definition, types, and functions of enzymes in the digestive system along with some important questions.

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What are Digestive Enzymes?

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The substances that help in the digestion of food are called digestive enzymes. These substances disintegrate food materials into simpler components to facilitate their absorption by the body. The digestive enzymes are primarily hydrolases and are present in the digestive tracts of all animals and plants.

Food is broken down into simpler molecules like sugars, fatty acids, amino acids, etc.

• Different enzymes are produced by different parts of the body. However, some digestive disorders prevent your body from making enough of them.
• It is essential to a have sufficient amount of enzymes as its deficiency can cause malnutrition. 
• Supplements or natural sources of digestive enzymes are used to improve digestion.

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Types of Digestive Enzymes

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On the basis of the target substrate, the enzymes in the digestive system can be classified into the following types:

Amylase

It is found in the human mouth as well as the pancreas. This digestive enzyme breaks down carbohydrates like starch into sugar.

• Pancrease produces pancreatic amylase which travels to the small intestine through a duct and completes the conversion of carbohydrates into glucose.
• Foods like rice and potato contain huge amounts of starch which gets broken down by the enzyme, amylase, into maltose.

Protease 

Protease enzymes are also known as peptidases. It is primarily found in the human stomach and pancreas. This breaks down peptide bonds present in proteins into smaller components called peptides. 

• Trypsin, Chymotrypsin, and Pepsin are the three types of protease enzymes.
• Pepsin is produced in the stomach, while trypsin and chymotrypsin are produced in the pancreas. 

Lipase 

It is primarily found in the human mouth, stomach, and pancreas. This enzyme helps to digest fats present in foods into simpler molecules.

• It breaks down dietary lipids – fats and oils – into smaller molecules like glycerol and fatty acids.
• The stomach produces a small quantity of lipase enzyme called gastric lipase.
• When dietary fats are converted into fat globules by bile juice, pancreatic lipases convert them into glycerol and fatty acids.

Nuclease

This enzyme helps in the breakdown of nucleic acids like RNA (ribonucleic acid) and DNA (deoxyribonucleic acid) into nucleotides by disintegrating the phosphodiester bonds.

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Functions of Digestive Enzymes

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Digestive enzymes are found in all parts of the human body. Some of these enzymes are: 

Digestive Enzymes in the Mouth

When we chew food, the salivary glands secrete various digestive enzymes present in the human mouth. These enzymes are: 

• Lipase Enzyme: This enzyme initiates the breakdown of fats or lipids in the mouth.
• Salivary Amylase or Ptyalin: Ptyalin helps in the breakdown of carbohydrates, mainly starch, into maltose.
• Lysozyme: This enzyme acts as an antiseptic agent against some of the non-essential nutrients like bacteria and viruses that might be present in the food.

Digestive Enzymes in the Stomach

Digestion of food begins in the stomach, therefore various digestive enzymes– gastric enzymes or juices– are secreted by the gastric glands. These are as follows:

• Pepsin: This is the most important of all gastric enzymes and is produced by the gastric chief cells. The gastric glands initially produce pepsinogen, which is the inactive form of the enzyme. Pepsinogen is then activated by the stomach acids to form pepsin. Pepsin is responsible for the breakdown of proteins into smaller peptides and amino acids.
• Gastric Lipase: This enzyme is acidic in nature and is secreted by the gastric chief cells present in the fundic mucosa of the stomach.This enzyme helps in the breakdown of dietary lipids present in the stomach. It produces hormones like hydrochloric acid, intrinsic factor, mucin, and gastrin.

Digestive Enzymes in the Pancreas

The pancreas secretes pancreatic juice which is composed of different digestive enzymes. These are as follows:

• Trypsinogen: This inactive protease is activated by the enzyme, enterokinase, into trypsin. Trypsin, in turn, is responsible for the breakdown of proteins into amino acids.
• Chymotrypsinogen: This inactive protease can also be activated by either enterokinase or trypsin enzyme, into chymotrypsin. Chymotrypsin, in turn, is responsible for the breakdown of proteins into aromatic amino acids.
• Carboxypeptidase: It is a protease that is responsible for the breakdown of proteins into amino acids.
• Pancreatic Lipase or Steapsin: It helps in the disintegration of emulsified fat into glycerol and fatty acids.
• Pancreatic Amylase: It is responsible for the digestion of the leftover starch into maltose.

Digestive Enzymes in the Small Intestine

• Secretin: It is a hormone secreted by the S cells of the duodenum (small intestine) in response to the acidity of the gastric chyme, which is a semi-liquid containing partially digested food. Thus, it aims to maintain the pH level of the duodenum.
• Cholecystokinin (CCK): It is an important peptide secreted by the ‘I cells’ of the small intestine in response to the gastric chyme containing high fat and protein. It is also responsible for decreasing gastric activity and emptying, thus, allowing the pancreatic juices to neutralize the acidic content of the gastric chyme. It also leads to gallbladder contraction, which, in turn, releases bile in the duodenum.
• Gastric Inhibitory Peptide (GIP): This peptide is produced by the mucosal cells present in the duodenum of the small intestine and is responsible for decreasing gastric motility.
• Motilin: This hormone is responsible for increasing gastrointestinal motility.
• Maltase: It is responsible for the conversion of maltose into glucose.
• Sucrase: It is responsible for the conversion of sucrose into glucose and fructose.
• Lactase: This is also an important enzyme found in the small intestine that is responsible for converting lactose (milk sugar) into glucose and galactose.

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Things to Remember

• The digestive enzymes are responsible for the breakdown of large food molecules into smaller components.
• Amylase can be found in pancreas and human mouth and is responsible for the breakdown of starch into maltose.
• Hydrolases are enzymes that act as catalyst to break down complex molecules into smaller ones with addition to water.
• Lipase enzyme is responsible for the breakdown of dietary lipids like fats and oils into fatty acids and glycerol.
• Nuclease helps in the breakdown of nucleic acids like RNA and DNA into nucleotides.