Blood is composed of plasma and formed elements. It transports oxygen, nutrients, wastes, and more throughout the body. Blood also helps regulate pH, temperature, water content, and protects against disease. Blood is made up of red blood cells, white blood cells, platelets, and plasma. Hematopoiesis is the process where blood cells are formed from stem cells in the bone marrow through the influence of growth factors like erythropoietin and thrombopoietin.