Andrea Cesalpino, working in the fourteenth century, was one of the first scientists to use the term "circulation," and to discuss the concept of a closed circulatory system. William Harvey did a great deal of work which cemented the concept of the closed circulatory system, combining data he obtained from dissections, experiments, and calculations. Our current understanding of the circulatory system was born of Harvey's work.

The circulatory system is a complex network of organs and tubes which serve to pump and carry blood throughout the body. The purpose of carrying blood throughout the body is two-fold: to deliver oxygen and other necessary substances to all of the tissues and organs throughout the body; to remove waste products, including carbon dioxide, from all of the tissues and organs.

Some species of organisms have open circulatory systems, meaning that the blood is not entirely enclosed in a...