header math Language Arts Social Studies Science test prep sign up  

Instruction 9-3

Discovery logo

Circulation | Digestive System | Digestive Enzymes | Kidney's Role | Respiratory System

Digestive Enzymes
CA HS Biology 9.f.
Digestive Enzymes assist the body in the breakdown of food. Different enzymes with different functions are produced in particular areas of the digestive tract.

Incomplete digestion may be a contributing factor in the development of many ailments including flatulence, bloating, belching, food allergies, nausea, bad breath, bowel problems and stomach disorders.

Digestive enzymes are primarily responsible for the chemical breakdown of food and constitute a large portion of digestive secretions. The human body makes approximately 22 different enzymes that are involved in digestion.

What is an Enzyme?

Enzymes are proteins produced by all living organisms, and, like all proteins, they consist of amino acids. What makes these proteins different from other proteins is how they behave in the body. By definition, enzymes are catalysts that make many essential biochemical reactions ‘happen’ and are not used up or chemically altered in the process. As a catalyst, they help a chemical reaction take place quickly and efficiently. Some reactions would either happen very slowly or not occur at all without enzymes. So a little bit of enzyme can effect a big change.

The same variety of amino acids that occur in all living things make up enzymes. The amino acids connect in particular sequences to form protein chains. The amino acids in the chain often bond together creating folding patterns and twisting into certain shapes. The particular folding pattern of each enzyme gives it distinct characteristics and functions. When anything disrupts the specific folding pattern, the enzyme often loses its ability to function, becoming inactivated or destroyed.

How do enzymes work?

Each type of enzyme has a special function and works in a particular way. Enzymes are essential to every aspect of life and carry out all the daily biochemical functions. They are the basic elements that activate all functions in the body, facilitate reactions that build compounds from the body’s raw materials, transport elements throughout the body, break down substances, and eliminate many unwanted chemicals in the body.

Enzymes are chemicals that facilitate other chemical reactions. Food itself is essentially just a mixture of chemicals that are broken down by enzymes. The released nutrients are the raw materials. Vitamins and other nutrients cannot work in the body by themselves. They require enzymes to transport them throughout the body and make use of them. Enzymes unlock the benefits of vitamins, minerals, proteins, and hormones and put them to work in the body. Enzymes are the workers and assist many biological, chemical, and metabolic reactions, but are not ‘alive’ themselves.
Sometimes particular enzymes need certain vitamins and minerals in order to function. Magnesium participates in over 300 enzyme reactions. These additional elements are called co-enzymes. A co-enzyme may give the enzyme the three-dimensional structure it needs to create the ‘active site’ necessary to perform its catalytic function. If a needed co-enzyme is not available, the enzyme will not function.

The body makes the following digestive enzymes and substances:


Saliva contains the enzyme salivary amylase. This enzyme breaks starch into smaller sugars and is stimulated by chewing. It is important to chew food thoroughly as this is the first stage of the digestive process.


The stomach is responsible for the digestion of protein. The parietal cells of the stomach secrete hydrochloric acid (gastric acid). Hydrochloric acid, along with pepsin, breaks down proteins to their individual amino acids.

Small intestine

The small intestine is divided into three segments and secretes a variety of digestive substances. The small intestine also receives secretions and enzymes from the pancreas, liver and the gallbladder. The first section, the duodenum, is primarily responsible for the absorption of minerals. The second section, the jejunum, absorbs water-soluble vitamins, protein and carbohydrates. The ileum is the final section of the small intestine and absorbs fat-soluble vitamins, fat, cholesterol and bile salts.


The pancreas produces digestive enzymes that act in the small intestine. These enzymes play a major role in digestion. The pancreas secretes about one and a half litters of pancreatic juice a day.

The enzymes produced by the pancreas include;

Lipases - Lipases function in the digestion of fats, oils and fat-soluble vitamins.
Amylases - These break down starch molecules into smaller sugars. Amylases also break down carbohydrates into maltose.
Proteases - are responsible for breaking down protein into smaller amino acids. Proteases include trypsin, chromotrypsin and carboxypeptidase.

Proteases are also responsible for keeping the small intestine free from parasites (intestinal worms, yeast overgrowth and bacteria). A lack of proteases can cause incomplete digestion that can lead to allergies and the formation of toxins.

Liver and gallbladder

The liver is the largest internal organ of the human body.

The liver produces bile that is either stored by the gallbladder or secreted into the small intestine. Bile emulsifies fats and fat-soluble vitamins. It also helps keep the small intestine free from parasites.

The liver metabolizes proteins, carbohydrates and cholesterol and is responsible for the detoxification of toxins, drugs and hormones.

Large intestine

The large intestine absorbs water, electrolytes and some of the final products of digestion.

Why Should I Care?

Enzymes run every function in our entire body. Digestive enzymes breakdown the food we eat so it can be used as a source of nutrients and a source of energy. Every cell relies on the raw materials provided to the body by digestive enzymes. If you do not have enough enzymes you can develop numerous illnesses. All the food and nutritional supplements you consume will not do any good if they are not sufficiently broken down and absorbed by the body.

Video Instruction
*Availability of You Tube video links may vary. eTAP has no control of these materials.


Cow Eye Dissection

Virtual Anatomy & Physiology of the Heart, Digestive System, Skeletal System, and the Brain

for Students, Parents and Teachers

Now let's do Practice Exercise 9-3 (top).

Next Page: Kidney's Role (top)