The liver produces most of the clotting proteins found in human blood plasma.
These proteins include fibrinogen and several clotting factors that work in a tightly regulated cascade after a blood vessel is damaged. The cascade ultimately helps convert fibrinogen into fibrin, forming strands that strengthen a developing blood clot.
The liver's role explains why serious liver disease can cause abnormal bleeding. A damaged liver may produce fewer clotting factors, while impaired bile production can also reduce absorption of vitamin K, which is required for producing several of them. Vitamin K is not itself a clotting protein.
Clot formation also depends on platelets, vessel-wall changes, calcium ions, and regulatory proteins. The liver is therefore central but not the only participant. The endothelium and bone marrow contribute other components involved in hemostasis.