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The small intestine is a long, highly convoluted tube in the digestive system that absorbs about 90% of the nutrients from the food we eat. It is given the name âsmall intestineâ because it is only 1 inch in diameter, making it less than half the diameter of the large intestine.
Absorption in the Mouth. Digestion begins in the mouth when food is mixed with saliva, containing digestive enzymes. Although there is a lot of chemical and mechanical activity during chewing, there is very limited nutrient absorption in the mouth. Some glucose absorption takes place in the mouth in the time the food is held for chewing -- less than a minute.