The Digestive System and the Liver - Sensing the right kind of food

Lips, eyes, and nose are generally given scant notice in discussions of the digestive process. But if we consider digestion to include selection of food and rejection of substances that might do us harm, then all three play very important roles.

The sensitive skin of our lips represents one of our first warning station that food may be harmful if taken into the mouth. It may tell us if a forkful of food is too hot or warn us of a concealed fishbone.

Our eyes, too, are important selection-rejection monitors for food. What else keeps us from sitting down to a crisp salad of poison ivy, or, less facetiously, popping a moldy piece of cake into our mouth?

As mammals’ noses go, man's is a very inferior and insensitive organ. Nevertheless, we make good use of our sense of smell in the selection and enjoyment of foods. The nose adds to our enjoyment of favorite food and drink not only before they enter the mouth, but also after, because stimulation of the olfactory cells in the nasal passages combines with the stimulation of the taste cells on the tongue to produce the sensation-and-discrimination gradations of taste.

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