Protein C and protein S

Protein C and protein S are glycoproteins, predominantly synthesized in the liver, that are important components of the natural anticoagulant system in the body. They are Vitamin K dependent and serve as essential components in the maintenance of physiologic hemostasis.

Proteins C is a precursor of the serine protease, activated protein C (APC). Its proteolytic activation by thrombin occurs on the surface of endothelial cells and involves thrombomodulin and endothelial PC receptor (EPCR).

Proteins S acts as a principal cofactor to protein C. The two work together to help regulate and control blood clot formation by inactivating specific coagulation factors (factors V and VIII) that are required to generate and form blood clots.

The protein C anticoagulant system provides important control over the blood coagulation cascade. Any alteration in this pathway, either hereditary, iatrogenic, or otherwise, may interfere with normal coagulation. Deficiencies in protein C and protein S are associated with thrombotic complications.
Protein C and protein S

Roles of calcium in blood clotting

When blood vessels rupture, the process of blood coagulation is quickly activated. Blood coagulation is adaptive response to hemorrhage involving local conversion of liquid blood to a gel, which plugs a wound.

Calcium participates in nearly every steps of the blood clotting cascade. Calcium is essential for the formation of fibrin, the fibrous protein that makes up structure of blood clots.

According to Best and Taylor’s theory, when the blood is shed from wound, thromboplastin is liberated from the damaged tissue and disintegrated platelets.

It acts on prothrombin in the present of calcium and converts it to active thrombin. Prothrombin is produced in the liver and is present in small quantities in the blood plasma. Calcium occurs as an inorganic constituent in the plasma.

Now thrombin reacts with fibrinogen and converts it into fibrin, which is insoluble. Fibrin constitutes the blood clot in which the blood corpuscles are trapped.

Blood will not clot in the absence of calcium but calcium levels in the body seldom fall low enough to significantly impair blood clotting.
Roles of calcium in blood clotting