Blood Terms



ABO blood group: Classification of blood based on the presence or absence of the inherited A and B antigens on the surface of red blood cells; consists of four blood types: O, A, B, and AB.


Agglutination: Clumping of cells in suspension, which settle out of the mixture; induced by crosslinking of the cells by agglutinating antibodies (agglutinins).


Albumin: The most abundant plasma protein; helps regulate the osmotic pressure of blood.


Anemia: Reduced oxygen carrying ability of blood. Hemorrhagic anemia is caused by sudden hemorrhage. Hemolytic anemia is caused by an increased rate of RBC destruction. Pernicious anemia is caused by lack of vitamin B12 in the diet, or deficiency of intrinsic factor. Aplastic anemia is caused by defective regeneration of bone marrow. Iron deficiency anemia is caused by inadequate hemoglobin content in RBCs, usually due to lack of iron in diet, or slow prolonged bleeding (such as heavy menstrual flow or bleeding ulcer). Sickle cell anemia is caused by a genetic disease characterized by sickle-shaped erythrocytes and accelerated hemolysis.


Basophil: Granular white blood cell that releases histamine and other mediators of inflammation; contains the anticoagulant heparin; its granules take up basic stain and turn blueish.


Chemotaxis: Movement of cells toward a chemical substance, such as white blood cells moving toward inflammatory chemicals.


Coagulation: Blood clotting; process in which blood is transformed from a liquid into a semisolid gel.


Diapedesis: Passage of white blood cells through intact blood vessel walls into tissue.


Embolus: A plug composed of a detached thrombus or foreign body that obstructs a blood vessel.


Eosinophil: Granular white blood cell that kills parasitic worms and destroys antigen-antibody complexes; its granules take up an acid stain called eosin and stain red.


Erythrocytes: Red blood cells (RBC) that transport most of the oxygen, O2 , to the body cells, and transport about ¼ of the carbon dioxide, CO2 , away from the body cells.


Erythropoiesis: The formation of red blood cells; a process of erythrocyte production and development that begins with stem cells in the bone marrow and ends with the release of mature erythrocytes into circulation; requires iron, vitamin B12 and the vitamin folic acid.


Erythropoietin (EPO): A hormone produced by the kidneys and liver in response to low oxygen levels that stimulates erythropoiesis.


Fibrin: Fibrous insoluble protein formed during blood clotting; the enzyme thrombin converts fibrinogen (soluble) into fibrin (insoluble), which forms the threads of the blood clot.


Globulins: A family of plasma proteins that include transport proteins and antibodies.


Hematocrit: The percentage of erythrocytes to total blood volume.


Hematopoiesis: Blood cell production, which occurs in red bone marrow after birth. Also called hemopoiesis.


Hemocytoblast: Hemopoietic stem cell formed in red bone marrow that gives rise to all of the formed elements of blood, such as erythrocytes, leukocytes, and platelets.


Hemoglobin: The iron containing respiratory protein that binds oxygen in red blood cells.


Histamine: Substance that causes vasodilation, increased permeability of capillaries, and constriction of bronchioles of the lungs; found in basophils, mast cells, and platelets that release it when cells are injured.


Heparin: Natural anticoagulant that is secreted into the blood by basophils.


Leukemia: Progressive proliferation of abnormal leukocytes; cancer of white blood cells.


Leukocytes: White blood cells (WBC); formed elements of the blood involved in body protection; functions include phagocytosis, inflammation, and immune responses.


Leukopoiesis: Formation and development of the various types of leukocytes (white blood cells).


Lymphocyte: Agranular white blood cell that helps carry out immune responses for the lymphatic system.


Macrophage: Actively phagocytic cells that are widely distributed in the body; participate in presenting antigens to lymphocytes; derived from monocytes.


Monocyte: Agranular white blood cell; phagocyte that develops into a macrophage in tissues.


Neutrophil: Granular white blood cell; active phagocyte that increases rapidly during acute infection; the most abundant type of white blood cell; its granules take up a mixture of acidic and basic stains and turn pale lilac.


Plasma: The noncellular fluid portion of the circulating blood.


Platelets (Thrombocytes): Cell fragments found in blood that lack a nucleus and are involved in blood clotting.


Polycythemia: Abnormal increase in the number of red blood cells (hematocrit above 55%).


Red bone marrow: A lymphoid organ that produces blood cells; located in spaces between trabeculae of spongy bone tissue.


Rh blood group: Subclassification of blood based on the presence or absence of the inherited Rhesus factor(Rh antigen, or D antigen) on the surface of red blood cells; consists of two blood types: Rh+ and Rh-.


Septicemia: The growth of pathogenic organisms in the blood. Also called sepsis, or blood poisoning.


Serum: The clear fluid portion of blood obtained after coagulation and centrifugation, which removes the fibrin clot and blood cells.


Thrombus: A stationary clot formed in an unbroken blood vessel that does not obstruct the vessel.