5/14 Now let us see how some portion of the body, say the right thumb, gets its share of food and of oxygen through the blood. We will start at the very beginning. The food, of course, is put into the mouth, chewed by the teeth, and softened and digested in the stomach and intestines. It is then taken up by the cells of the mucous coat of the intestines and passed into the network of tiny blood-pipes surrounding them, between the lining of the bowels and their muscular coat. These tiny blood-pipes, called _capillaries_, run together to form larger pipes--the small veins; and the small veins from the walls of the intestine and stomach finally run together into one large pipe, or trunk-line (called the _portal vein_), which carries them to the liver. |