Heparin is generally synthesized primarily in the liver and, to a lesser extent, in tissues such as the lungs, blood vessel walls, and intestinal mucosa. 1. Liver: Heparin, named because it is firstly found in the liver, is mainly synthesized in the liver, and consists of mucopolysaccharide sulfate lipid alternately composed of glucosamine, L-aiduglycoside, N-acetylglucosamine and D-glucuronic acid, with an average molecular weight of 15KDa, and is strongly acidic. 2. Lung, blood vessel wall, intestinal mucosa, etc.: It is also found in lung, blood vessel wall, intestinal mucosa and other tissues. Heparin, as a commonly used anticoagulant nowadays, occurs naturally in mast cells and is now mainly extracted from the mucosa of bovine lungs or porcine small intestine. Heparin has the ability to enhance the affinity of antithrombin, inhibit platelet aggregation, and stimulate the release of anticoagulant substances from the cells of blood vessels, making it a natural anticoagulant substance in animals. Heparin has anticoagulant effects both in vivo and in vitro, and is mainly used clinically for thromboembolic diseases, myocardial infarction, cardiovascular surgery, cardiac catheterization, extracorporeal circulation, hemodialysis, and so on. With the progress of pharmacology and clinical medicine, the application of heparin is expanding.