Before your body can use the food you eat for fuel, as well as for cell and tissue growth, the food has to go through the process of digestion. The digestive process begins in the mouth and continues in the stomach, where certain enzymes begin to break down foods into their basic components so cells can use them.
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Enzymes Play a Major Role
Enzymes are proteins that act as catalysts, which means that they help chemical reactions occur within the body. There are many different enzymes -- and like a key with a lock, each enzyme works only on a certain substance, or substrate. The enzymes in the mouth and stomach include amylase, lipase and pepsin -- and each is responsible for helping to start the digestion process for carbohydrates, fat and protein.
It Starts in the Mouth
Digestion starts when food is chewed and broken down into small pieces. Saliva contains the digestive enzyme, amylase, which works on carbohydrate starches, like breads, potatoes, or pasta, to help break them down into simple sugars. Some digestion of fat also starts in the mouth when a small amount of lingual lipase is secreted and mixes with saliva. However, most of the lipase enzymes that digest fat come from the stomach -- and primarily the pancreas.
Next Stop, the Stomach
After food is chewed and mixed with saliva, it passes through the esophagus, and into the stomach, where several more enzymes help with digestion. Once in the stomach, protein starts to break down into peptides when the stomach lining excretes the enzyme, pepsin. Fat digestion continues a bit more with the help of some gastric lipase, while it is prepared for further digestion in the small intestine by pancreatic lipase. Food that is partially digested by chewing and the action of enzymes in the mouth and stomach is called chyme. This mixture is then ready for the final stage of digestion, which takes place in the small intestine with the help of many more enzymes from the pancreas.
Like each of the systems within the human body, the digestive system is extremely complicated and runs like a finely tuned machine. The digestion that occurs in the mouth and stomach is just the start of a complex process that involves many nerves, hormones and organs all working together to break down and use all of the foods and liquids you consume each day.