Physiologically, blood transports oxygen from the lungs to all the cells in the body. Blood transports nutrients from the digestive organs to the cells in the body. Blood transports waste products from cells to kidneys, lungs and sweat glands. Blood transports hormones from endocrine glands to target cells. 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.