There are several types of digestive system enzymes, each designed to break down different parts of food, which can be found at different points in the digestive system. The main categories of enzymes are amylase, lipase, protease, and nuclease. Glands in the mouth, stomach, small intestine, and pancreas secrete some or all of these as food passes along the digestive tract so that it may be broken down and used by the body. The majority of digestive enzymes are found in pancreatic juice, though they are also present in saliva and gastric digestive juices.
One of the first enzymes to start the process of digestion is amylase. This type of enzyme is designed to break down carbohydrates into simple sugars that the body can process. It is first secreted into the mouth by the salivary glands, where it begins digesting foods such as fruits, vegetables, and beans. More amylase is then produced by the pancreas and sent to the small intestine, where it continues to help break down carbohydrates. There are several subcategories of amylase, each designed to process certain types of carbohydrates; for example, lactase breaks down milk sugars and sucrase breaks down complex starches and sugars.
Protease is the group of digestive system enzymes that breaks down proteins contained in meats, nuts, and cheeses. The stomach and the pancreas create protease, so processing of proteins starts further into the digestive system than carbohydrates. Protein needs to be broken down into amino acids, which are critical for all cells to function. The main types of protease found in the human body are pepsin and peptidase.
Another of the digestive system enzymes is lipase. Lipase's function is to break down fats, such as those found in oils, meat, and dairy. Some lipase is generated in the mouth and stomach, but most of it comes from the pancreas and does its work in the small intestine. Here it works with bile, generated by the liver, which emulsifies the large fat molecules, making them smaller so the lipase can then break it down further into glycerol and fatty acids.
The pancreas also generates the final of the digestive system enzymes, nuclease. This enzyme is made to break down nucleic acids such as DNA and RNA. It acts to separate the bonds between nucleotides, which then release nitrogen and simple sugars.
