Blood transports enzymes to specific cells. Blood regulates pH levels via buffers and amino acids. Because of the water content in blood, blood regulates the water content of cells primarily through dissolved sodium ion levels. Blood prevents body fluid loss through clotting. Blood, lastly, protects us against toxins and foreign microbes via special combat unit cells.
Blood is composed of plasma and formed elements.
The process by which all blood cells are produced is called hemopoiesis or hematopoiesis. Note the various stages through which all cells must go prior to becoming more or less mature. This shape increases the surface area for diffusion of gases. They have no complex metabolic activities. Cell death occurs at about 120 days.