Blood is made up of two broad types of cells (red Blood Cells and white blood cells) and specialized cell fragments called platelets Red blood cells are the most numerous cells in the body. The fully mature red cell extrudes its nucleus and appears in the circulation full of hemoglobin its shape is that of a biconcave disk. Hemoglobin carries oxygen to the tissues Known also as leukocytes, white blood cells are produced in red bone marrow and lymphatic tissue They defend the body from viruses, bacteria and other microbes, and invertebrate parasites. There 9. 10. are five major types: neutrophils, eosinophils, basophils, monocytes, and lymphocytes Platelets are the smallest structural units in the blood. They are formed in the bone marrow from the cytoplasm of giant cells known as megakaryocytes. 11. 12. 13..