Antithrombins are substances that prevent the formation or promote the dissolution of blood clots (thrombi). They include:

1. Anticoagulants: These are medications that reduce the ability of the blood to clot. Examples include heparin, warfarin, and direct oral anticoagulants (DOACs) such as apixaban, rivaroxaban, and dabigatran.
2. Thrombolytic agents: These are medications that break down existing blood clots. Examples include alteplase, reteplase, and tenecteplase.
3. Fibrinolytics: These are a type of thrombolytic agent that specifically target fibrin, a protein involved in the formation of blood clots.
4. Natural anticoagulants: These are substances produced by the body to regulate blood clotting. Examples include antithrombin III, protein C, and protein S.

Antithrombins are used in the prevention and treatment of various thromboembolic disorders, such as deep vein thrombosis (DVT), pulmonary embolism (PE), stroke, and myocardial infarction (heart attack). It is important to note that while antithrombins can help prevent or dissolve blood clots, they also increase the risk of bleeding, so their use must be carefully monitored.

Antithrombin proteins are a type of protein found in the blood that inhibit the formation of blood clots. They work by binding to and neutralizing thrombin and other coagulation factors, such as factor Xa, that are involved in the coagulation cascade. Antithrombin proteins are an important part of the body's natural anticoagulant system, which helps to prevent excessive clotting and maintain proper blood flow.

Antithrombin proteins can be increased through the use of medications such as heparin, which binds to and enhances the activity of antithrombin. This is why heparin is often used as a treatment for conditions associated with abnormal blood clotting, such as deep vein thrombosis or pulmonary embolism.

It's worth noting that while antithrombin proteins are important for preventing excessive clotting, having too few of these proteins can also be a problem, as it can increase the risk of abnormal bleeding.

Heparin is defined as a highly sulfated glycosaminoglycan (a type of polysaccharide) that is widely present in many tissues, but is most commonly derived from the mucosal tissues of mammalian lungs or intestinal mucosa. It is an anticoagulant that acts as an inhibitor of several enzymes involved in the blood coagulation cascade, primarily by activating antithrombin III which then neutralizes thrombin and other clotting factors.

Heparin is used medically to prevent and treat thromboembolic disorders such as deep vein thrombosis, pulmonary embolism, and certain types of heart attacks. It can also be used during hemodialysis, cardiac bypass surgery, and other medical procedures to prevent the formation of blood clots.

It's important to note that while heparin is a powerful anticoagulant, it does not have any fibrinolytic activity, meaning it cannot dissolve existing blood clots. Instead, it prevents new clots from forming and stops existing clots from growing larger.