This program is best viewed using Macromedia Flash. Download the autoloadable plugin.
Blood is pumped from the heart through large blood vessels to the kidneys.
The kidneys are about the size a fist, and lie in the back. They are partly protected by the lower ribs. Each kidney contains about a million filters. Inside the kidney the blood vessels continue to divide until they become so small that they can no longer hold water. These tiny vessels are known as capillaries.