A healthy empty stomach seen at gastroscopy. Note the folds called rugae. They allow the stomach to expand and contract when you eat a big meal. Note the normal healthy pink color.
Most animals, including human beings, have a single stomach, but birds and cows, and sheep have two or more chambers to their stomachs. Empty, the volume of your stomach "pouch" is less than one-half cup. As you eat, its muscular wall can relax and expand to hold about three pints of sustenance. Then about every twenty seconds, contractions called peristaltic waves ripple through your stomach squeezing gently in the upper part, more powerfully lower down. This churning motion mixes the food particles with powerful hydrochloric acid and the enzyme, pepsin. Produced by the stomach, these strong chemicals convert the food to about the consistency of cream of potato soup. Eventually, the now liquefied food is squirted a little bit at a time through another one-way valve and into the small intestine. Only water, alcohol, and certain drugs seem to be absorbed by the stomach; most food absorption takes place in the small intestine.
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