What is the humoral coagulation system?

The humoral coagulation system, also known as the intrinsic pathway, is one of the two main pathways involved in blood coagulation, or the process by which blood forms clots to stop bleeding. It is activated when blood comes into contact with a foreign surface or damaged tissue.

The humoral coagulation system involves a series of sequential biochemical reactions that ultimately lead to the conversion of prothrombin into thrombin. Thrombin then converts fibrinogen into fibrin, which forms the insoluble strands that create the blood clot.

The steps involved in the humoral coagulation system are as follows:

Activation of factor XII (Hageman factor): This occurs when factor XII comes into contact with a negatively charged surface, such as damaged blood vessels or collagen.

Activation of factor XI (plasma thromboplastin antecedent): Factor XI is activated by factor XIIa (activated factor XII).

Activation of factor IX (Christmas factor): Factor IX is activated by factor XIa (activated factor XI) in the presence of calcium ions and platelet factor 3 (PF3).

Activation of factor X (Stuart factor): Factor X is activated by factor IXa (activated factor IX) in the presence of calcium ions and PF3.

Conversion of prothrombin to thrombin: Factor Xa (activated factor X), in the presence of calcium ions, PF3, and factor V (proaccelerin), converts prothrombin into thrombin.

Conversion of fibrinogen to fibrin: Thrombin converts fibrinogen, a soluble protein present in blood plasma, into insoluble fibrin strands. These strands form a meshwork that traps platelets and red blood cells, creating a blood clot.

The humoral coagulation system works in conjunction with the cellular coagulation system, or the extrinsic pathway, to ensure efficient and timely blood clotting. Both pathways ultimately converge at the activation of factor X, leading to the formation of thrombin and fibrin.