Heparin (from Greek "hepar" meaning "liver" is an injectable anticoagulant.
What is heparin?
It's a drug, that prevents blood from clotting, which we call an anticoagulant. It's injected, as supposed to warfarin which you take by mouth.
Is it related to hepatic... the liver?
Strangely... yes, it is linked with the liver. The link is that it was originally isolated from the liver cells of dogs.
Highly sulfated glycosaminoglycan, having the highest negative charge density of any known biological molecule
Usually stored within the secretory granules of mast cells, and released only into the vasculature at sites of tissue injury
It's true physiological role in the body remains unclear, because blood anticoagulation is mostly achieved by heparan sulfate proteoglycans, derived from endothelial cells. Also, it is found in some animals that don't have a blood coagulation system → It is proposed that rather than anticoagulation, it's main purpose is defense at such sites against invading bacteria, and other foreign material
In nature, it is a polymer of varying chain size
Activates antithrombin III (which blocks thrombin from causing blood clotting). It is usually made from pig intestines
So how does this drug used to prevent blood from clotting, found in the liver of dogs, exactly work?
It works by activating antithrombin 3, increasing its activity manyfold. Specifically, it increases the binding of antithrombin 3 to factor 2 and 10.
What is antithrombin 3?
It's a protein that inactivates several enzymes of the blood clotting system, thereby stopping clotting. So, hearin therefore prevents blood from clotting.
Unfractionated heparin is heparin that hasn't been fractionated to sequester the fraction of molecules w/ a low molecular weight
Low-molecular-weight heparin (LMWH) is a derivative of heparin, that has undergone fractionation to make it's pharmacodynamics more predictable. It's advantage is that it's effects are more predictable than unfractionated heparin, and doesn't require monitoring for APTT coagulation (having more predictable plasma levels), and fewer side effects. The disavantage is that the effect of the antidote protamine sulfate, results in only limited reversibility. Examples include Enoxaparin sodium (Clexane)