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An Overview of how the Digestive System Works
After eating, our digestive system starts to work on the nutrients so they can be absorbed and used by the body. The digestive system does this by breaking down the complex foods into more simple nutrients by enzymatic action.
The first part of this process takes place in the mouth. After chewing the food thoroughly an enzyme (ptyalin) in the saliva breaks down complex carbohydrates (starches) into more simple sugars. After the food has been softened it is then pushed down the esophagus into the stomach.
Not much digestion actually takes place in the stomach. The only thing that is readily absorbed by the stomach is alcohol. The stomach creates an acidic environment (hydrochloric acid) for the enzymes to work in. The predominant stomach enzyme is pepsin which breaks down proteins into short chains of amino acids which can be used by the body. Most other nutrients are digested only after the food moves on out of the stomach, approximately three to four hours later.
The small intestine, the duodenum, jejunum and ileum have an alkaline environment and this is where digestion is completed after most nutrients have been absorbed. The specialized absorbing cells, enterocytes, are distinguished by numerous microvilli that greatly increase the absorptive surface area.
The pancreas secretes pancreatic juice into the duodenum. Pancreatic juice contains a number of enzymes that are used to absorb the nutrients remaining in the food. Lipase which breaks up fatty substances into fatty acids and monoglycerides, protease splits up protein and amylase which converts starch to sugar.
After most nutrients have been assimilated the food moves on into the colon or large intestine. The principle functions of the large intestine are to concentrate, store, and excrete food wastes. The colon contains large numbers of bacteria, which produces enzymes that act on the remaining food residues and fiber. The products of this bacterial digestion and fermentation include short-chain fatty acids and gases such as carbon dioxide, methane and hydrogen. The food is held while water is absorbed from it before it is eliminated.
Certain foods, including most fast foods, have an adverse effect on the digestive process and ones health. These inappropriate foods are well known to most people but are not usually considered to be detrimental and are consumed far to often in the Western Diet.