Q. From where does the blood obtain these elements ?
A. The oxygenation of the blood is carried out in the lungs by the process of respiration, which, at the same time, rids the blood of carbon dioxide. Carbon dioxide is produced by metabolic processes in the tissues and is carried by the blood in the veins. Water and nutrients are added to the blood by the alimentary canal, i.e., the intestines.
Q. How do the arteries 'deliver their goods' to the tissues ?
A. As explained above, as the arteries reach their destination, i.e., the tissues, they divide and subdivide and finally break up into the finest vessels, namely, the capillaries, which are spread out into the tissues. It is through the capillaries that the plasma (watery part of the blood) bathes every one of the millions of cells of our body. It is here that oxygen, water and nutrients are delivered to the tissues and waste products of metabolism and carbon dioxide are removed from the cells and absorbed into the blood.