A human being is a complex set of interconnected organ systems functioning as an integrated whole. Each of these organ systems is made of identical cells, which are the powerplants and the workhorses of the human body. By most calculations, the number of cells is somewhere between 50 and 70 trillion. To put size in perspective, if a human being was the size of the earth, which is 8000 miles in diameter, a cell would be 2 feet wide. The work of the cell is unseen to the na