Hematology is the study of blood, blood forming organs, and blood disorders. Blood is a connective tissue that circulates through the body, delivering oxygen and nutrients to cells and removing waste. Hematopoiesis is the formation of blood and its components. The two major components of blood are plasma and formed elements. Plasma is the liquid part of blood and helps fight infections and transport nutrients and waste. Formed elements are blood cells and cell fragments, including red blood cells, white blood cells, and platelets, which are cell fragments.