The circulatory system serves to move blood to a site or sites where it can be oxygenated, and where wastes can be disposed. Circulation then serves to bring newly oxygenated blood to the tissues of the body. As oxygen and other chemicals diffuse out of the blood cells and into the fluid surrounding the cells of the body's tissues, waste produces diffuse into the blood cells to be carried away. Blood circulates through organs such as the liver and kidneys where wastes are removed, and back to the lungs for a fresh dose of oxygen. And then the process repeats itself. This process of circulation is necessary for continued life of the cells, tissues and even of the whole organisms. Before we talk about the heart, we should give a brief background of the two broad types of circulation found in animals. We will also discuss the progressive complexity of the heart as one moves up the evolutionary ladder.
Hank takes us on a trip around the body - we follow the circulatory and respiratory systems as they deliver oxygen and remove carbon dioxide from cells, and help make it possible for our bodies to function.