Digested water, minerals and molecules of food are then absorbed from the cavity in the upper portion of the small intestine. Most of these molecules then cross the mucosa into the bloodstream, which carries them throughout the body where they are stored until needed.
Protein
Proteins consist of large molecules that have to be digested by enzymes before they build and repair tissues throughout the body. Enzymes in stomach acid begin the process of digesting protein. This process is completed when the protein enters the small intestine. Here, enzymes from the intestinal lining and from the pancreas break the large protein molecules into amino acid, which is absorbed into the blood and carried throughout the body to build parts of body cells, including cell walls.
Carbohydrates
Total daily calorie intake is recommended to be 55 to 65 percent carbohydrates. Carbohydrates are found in such foods as breads, legumes, pasta, potatoes, rice, fruits and vegetables. These foods contain both fiber and starch. Carbohydrates are broken down into small molecules by saliva and pancreatic juices by the lining of the small intestine. Saliva and pancreatic juices break starch into molecules call maltose. Then, the juices in the small intestine transforms the maltose into glucose molecules that are absorbed by the blood. Glucose moves through the bloodstream to the liver. Here, it is stored and used when the body requires energy.
Table sugar is also a carbohydrate and it has to be digested in order to be used by the body. Table sugar is digested by an enzyme in the small intestine, which turns the sugar into fructose and glucose. These are then absorbed from the cavity in the intestine into the bloodstream.
Another type of glucose is lactose, which is found in milk and milk products. It is broken down into digestible molecules by the enzyme lactase, which can be found in the lining of the small intestine. People who are lactose intolerant are unable to produce enough lactase to digest milk and milk products.
Vitamins
Vitamins from food are a vital part of our food supply. Vitamins are absorbed by the small intestine.