3.3 Taking the nutrients around the body

The blood system delivers the products of digestion to all parts of the body (Figure 10).

Figure 10 Blood system, showing the organs for digestion and the exchange of oxygen and carbon dioxide

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The diagram shows the route blood takes to distribute nutrition around the body, with the following labels (from the top, clockwise): head and forelimbs, pulmonary artery, lung, pulmonary vein, aorta, kidneys, trunk and legs, O₂, CO₂, vein, liver, hepatic vein, heart, lung, O₂, CO₂, anterior vena cava.

Figure 10 Blood system, showing the organs for digestion and the exchange of oxygen and carbon dioxide

Arteries take the blood away from the heart to all of the various parts of the body. There, the arteries branch into smaller and smaller blood vessels, until they form tiny capillaries. Capillaries are damaged when you get a small cut, graze or bruise. The capillaries then rejoin to take the blood back to the heart again, in veins.

Pictures of the body are always drawn as though you are facing the person. So the right side of the heart appears on the left side of Figure 10 and vice versa. The blood enters the right side of the heart in the big vein called the vena cava. From there it is pumped to the lungs, to pick up oxygen. Then it travels back again to the heart and sets off in the big artery called the aorta, back around the body again. Some of it goes to the intestines and, as already mentioned, there is then a special vein taking the blood from the small intestine to the liver, to carry the digested food.