The digestive tract is a series of hollow organs joined in a long, twisting tube from mouth to anus. The function of the digestive tract is to break down food and absorb nutrients, which it does with the assistance of the pancreas and liver. The digestive tract, liver and pancreas create digestive juices that contain a mix of different enzymes, each enzyme targeted toward a particular substance ingested. The hollow organs that make up the digestive tract are the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus.
Mouth
Digestion begins when food enters the mouth. The mouth contains salivary glands, and the saliva produced by these glands contains the enzyme amylase. Chewing assists digestion and increases the surface area that amylase can target. Amylase breaks down complex carbohydrates, such as starch, into smaller components or even simple sugars. Foods high in complex carbohydrates include rice, potatoes and wheat.
Stomach
The digestive glands in the stomach are highly specialized. They help to digest food through the production of stomach acid. However, these glands also produce pepsin, which is an enzyme that helps to break down protein. Pepsin digests protein through fragmentation, producing smaller peptides and amino acids, which can be absorbed by the intestine. When the food leaves the stomach, the partially digested food passes into the small intestine, where the digestive juices produced by the liver and pancreas are added to the mix.
Intestine
The digestive juice produced by the liver is known as bile, which is stored in the gallbladder and released into the small intestine when needed. The main function of bile is to dissolve fat, allowing it to be cleaved by enzymes from the intestine and pancreas. The intestine is lined with structures called villi, which harbor several enzymes. These enzymes include dextrinase, maltase, sucrase and lactase, which break down sugars, as well as enzymes that cleave peptides and amino acids, such as aminopeptidase and dipeptidase.
Pancreas
The pancreas contains a set of cells known as acinar cells, which are responsible for the production of digestive enzymes. The enzymes present in pancreatic juice are able to digest carbohydrates, proteins and fats. Pancreatic amylase works in the same way as amylase in the saliva, breaking down large carbohydrate molecules into sugars. Trypsin, chymotrypsin and carboxypeptidase are responsible for the digestion of proteins, whereas pancreatic lipase is used to break down fat.
