Plasma, white blood cells, red blood cells, and platelets. The main function of blood is that it transports substances between body cells and the external environment. The average blood volume in a human body is 5 liters (4-5 for women, 5-6 for men) A hematocrit is the amount of red blood cells, usually 45% of blood volume. They are biconcave discs that are thin near the centers to increase surface area for transporting gases. Erythrocytes extrude nuclei to make more room for hemoglobin. Hemoglobin is the oxygen carrying protein which gives blood its color. Anemia is the decreased capacity to carry oxgyen. Excessive loss or destruction of rbcs or hemoglobin. Opposite- polycythemia: too many rbcs- think blood leading to blood clots (blood doping using erythropoietin) Leukocytosis: total number of wbc"s exceeds 10,000. Leukopenia: total number of wbc"s below 5000. Name the 5 types of leukocytes and describe their functions. Lobed nucleus with 2-5 sections, dark staining nucleus and pale granules.