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The digestive system is important because it breaks down foods to their simplest components--fatty acids and glycerol, amino acids and glucose. The amino acids and glucose can be absorbed in the villi(tiny hair-like projections in the small intestine) and enter the circulating blood via capillaries. The fatty acids however, take a different pathway. Inside the vill, are lacteals which absorb the fatty acids and these travel in the circulating lymph fluid. Eventually, in the neck region, the lymph re-enters the bloodstream once again. Therefore, there is a close connection in the small intestine with the circulatory system. Also, the blood travels through the aorta which has smaller branches to supply all the organs of the body, including the digestive system, with necessary substances including oxygen, nutrients and to remove wastes.
The digestive system or gastrointestinal system is linked to the circulatory system because the blood in the circulatory system receives nutrients from the gastrointestinal tract. Food must be broken down into simpler substances before it can be used by the body. This is accomplished by mechanical and chemical means. The chemical digestion of carbohydrates, for example, begins in the mouth. Food in the stomach and duodenum (first part of the small intestine) is broken down by additional mechanical churning and enzymatic activity.
Only when food has been completely broken down can it be absorbed by the blood stream and used as fuel for the body. This absorption occurs in the stomach, small intestine (bowel), and large intestine. An example is:proteins must be broken down into amino acids before the body can use them.
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