ABSTRACT
The watery environment in which single-cell organisms live provides them food and removes their wastes, a function that the human circulatory system similarly provides for the 60 to 100 trillion cells in a human body. The circulatory system brings each cell its daily supply of nutritive amino acids and glucose and carries away waste carbon dioxide and ammonia, which will be filtered out of our systems and flushed away through micturition and excretory functions. The heart, the center of our circulatory system, keeps blood moving on its predetermined circular path, a function so essential that if the pump fails we quickly fail as well-and we die.
