heparin /hep″ərin/ [Gk, hēpar, liver] , a naturally occurring mucopolysaccharide that acts in the body as an antithrombin factor to prevent intravascular clotting. The substance is produced by basophils and mast cells, which are found in large numbers in the connective tissue surrounding capillaries, particularly in the lungs and liver. In the form of sodium salt, heparin is used therapeutically as an anticoagulant. See also heparin sodium.
