William Harvey's classic work became the foundation for all modern research on the heart and cardiovascular medicine. Further, his work is considered to be one of the most important contributions in the history of medicine. Without the understanding of the circulatory system made possible by Harvey's pioneering work, the medical miracles that we think are commonplace would be impossible. Let's take a few moments to discuss the hearts and circulatory systems found in a variety of animals. The Types of Circulatory Systems Remember that the circulation of the blood 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.