Many persons labor under a misapprehension as to the role the stomach plays in the digestion of food elements and the absorption of digested nutrients. The stomach only begins to digest proteins and does next to nothing about the carbohydrates (the starches and the sugars) or the fats. Absorption in the stomach appears to be limited to minimal amounts of sugar and alcohol. In fact, some persons have gotten along fairly well with most of their stomach removed. In such instances this marvelous chemical plant automatically accommodates itself to the new circumstances​—the small intestine expands its forepart to pouchlike proportions and so manages to take the place, in effect, of the stomach.

What the stomach does is to prepare the food it receives so that it is suitable for further processing in the intestines. By both chemical and mechanical action it breaks down the food particles until they become something like a grayish medium-thick pea soup called “chyme.”

At regular intervals, and automatically, the stomach squeezes some of this chyme through its lower valve (it also has an upper valve). Now take a look at this lower valve of the stomach; it keeps the chyme in the intestines from backing up into the stomach. Because the quantity of digestive juices added to the food mass in this chemical plant is more or less equal to the nutrients absorbed into the bloodstream, the chyme maintains about the same consistency as it moves throughout the twenty-three feet of the small intestine.

In this chemical plant not only are digestive juices supplied through the innermost coating of the intestine, but digestive juices are also received from two other sources. The liver, by means of a tube, supplies bile for breaking down the fats. And the pancreas, by means of two tubes, supplies basically three kinds of enzymes.a These are for the digestion of proteins, carbohydrates and fats. Certain glands in this chemical plant serve to neutralize the acidity of the chyme received from the stomach. Yes, the job done by the stomach requires an acid medium, while that done in the small intestine requires one that is alkaline.

After the food has been digested it needs to be absorbed. In fact, digestion and absorption go on at the same time without interfering with each other. The absorption is by means of these tiny conical projections that you see in the innermost lining of this tube. They act like suction pumps. By means of them the digested protein and carbohydrate elements go directly into the blood. The digested fat particles, however, first enter the lymph, and from there go into the bloodstream.