Absorption and Transport of Nutrients
Now that you have the road map to your digestive system, along with the lowdown on its accessories, let's see how everything works together to give your body all the nutrients you need.
- Carbohydrates: Remember that ham and cheese sandwich we followed earlier? The bread is made up largely of carbohydrates, which begin to break down when you take that first bite. They continue to be broken down by the digestive juices in the pancreas and small intestine lining and are then absorbed in the small intestines, where they enter the bloodstream. The starch in the bread is broken down in much the same way, but with an extra step. Its breakdown produces glucose, which is stored in the liver and provides you with energy.
- Protein: The ham consists of protein molecules that need to be digested -- protein is the key player in building and repairing your body tissues. Enzymes first attack these molecules in the stomach, and they're finished off in the small intestine with help from enzymes and those handy pancreatic and intestinal lining juices. Then the smaller protein molecules become known as amino acids. They're now small enough to be absorbed through the small intestine and right into the blood.
- Vitamins: While our food is digested, vitamins are absorbed in the small intestine. There are two basic types of vitamins in the food we eat: water-soluble and fat-soluble. The water-soluble vitamins (B vitamins and vitamin C) are absorbed easily along with the water in the small intestine, where they then travel through the body via the blood vessels. Fat-soluble vitamins (vitamins A, D, and K) are absorbed just like the fat mentioned above. Once absorbed, however, they are stored for long periods of time in cells called lipocytes. Water-soluble vitamins don't stay in your body for long -- extra amounts of these are usually eliminated in a quick trip to the bathroom.