HSC 4555 Lecture Notes - Lecture 7: Erythropoietin, Tachycardia, Leukocytosis
Document Summary
Of the 4 to 6 l of blood in the circulatory system, approximately 45% is blood cells and 55% is plasma. The plasma fraction contains dissolved substances, including nutrients, ions, plasma proteins, metabolic wastes, hormones, and enzymes. Red cells function to carry oxygen and carbon dioxide in the blood. They have a limited life span of 80 to 120 days because they contain no cytoplasmic organelles and thus are incapable of replacing lost or damaged cellular components. The normal red cell concentration is 4. 2 to. Leukocytes, or wbcs, are the other cell type present in blood. Leukocytes circulate in much lower numbers than rbcs (5000 to 10,000/mm3). Platelets are not cells but are small fragments of megakaryocytes. The normal platelet count is 150,000 to 400,000 cells/mm3. Red cell development from pluripotential stem cells in the bone marrow is stimulated by a hormone growth factor called erythropoietin.
