Exogenous coagulation factor

There are three pathways of blood coagulation in the human body, and exogenous coagulation factors are only one of them, which also include intrinsic coagulation pathway and common coagulation pathway. Exogenous coagulation is mainly a reaction due to tissue damage. If this happens, stay optimistic, seek medical attention, and adjust your condition according to the doctor's advice. Don't be too anxious and it will improve slowly.

Extrinsic coagulation pathway

Exogenous coagulation pathway: refers to the fact that not all participating coagulation factors exist in the blood, and external coagulation factors are also involved in hemostasis. This process starts when tissue factor is exposed to the blood and ends when factor X is activated. In clinical practice, prothrombin time is used to reflect the status of the extrinsic coagulation pathway. Tissue factor is a specific transmembrane protein present in the plasma membrane of various cells. When tissue is damaged, this factor is released and, with the participation of calcium ions, it forms a 1:1 complex with factor VII. It is generally believed that factor VII or tissue factor alone has no procoagulant activity. However, when factor VII binds to tissue factor, it will be quickly activated to VIIa by activated factor X, thus forming VIIa tissue factor complex, which is 16,000 times more potent than VIIa alone in activating factor X. Exogenous coagulation takes a short time and reacts rapidly. The extrinsic coagulation pathway is primarily regulated by tissue factor pathway inhibitor (TFPI). TFPI is a glycoprotein present in normal human plasma, platelets and vascular endothelial cells. It inhibits the activity of factor Xa or factor VIIa-tissue factor by binding to factor Xa or factor VIIa-tissue factor-factor Xa to form a complex. In addition, studies have shown that the intrinsic and extrinsic coagulation pathways can activate each other.

What are the exogenous coagulation factors?

(1) If coagulation is initiated by the release of factor III due to tissue damage and the formation of prothrombin activator, it is called extrinsic coagulation.

(2) Coagulation step:

① Extrinsic coagulation is initiated by the release of factor III due to tissue damage. Factor III and factor VII form a complex and, in the presence of Ca2+, activate factor X to become factor Xa.

② Factor III is a phospholipid protein that is widely present in extravascular tissues, especially in the brain, lungs and placenta. The role of Ca2+ is to bind both factor VII and factor X to the phospholipids provided by factor III so that factor VII can catalyze factor X and activate it into factor Xa.

③ After factor Xa is formed, the process of extrinsic coagulation becomes the same as that of intrinsic coagulation.

Generally speaking, the extrinsic coagulation process is simpler and faster, while the intrinsic coagulation process is more complicated and slower. But in fact, extrinsic coagulation is closely related to intrinsic coagulation and exists simultaneously in the body's coagulation process.

(3) The role of factor VIII: Factor VIII is originally inactive in plasma and needs to be activated by factor IIa to be converted into factor

VIIIa. When factor IIa hydrolyzes factor I into fibrin monomers and connects them into polymers, their structure is unstable. Only after the action of factor VIIIa can they become strong fibrin polymers, that is, water-insoluble fibrin is generated, thus forming a blood clot.