Coagulation of Blood

Introduction

The process of clotting of blood is known as coagulation of blood. Coagulation is the transformation of blood from a liquid to a gel that results in the formation of a blood clot. Coagulation is a crucial and complex procedure that permits blood to plug and mend wounds. 

Coagulation can lead to haemostasis, or the halt of blood loss from a damaged vessel, and then repair. Coagulation of blood is caused by platelet activation, adhesion, and aggregation, as well as fibrin deposition and maturation. In addition, the body stops any unusual bleeding and helps to prevent the loss of blood.

Ionised calcium (Ca++) is found in the blood and in intracellular sources. Phospholipids play an important role in the membranes of both cells and platelets. They provide a surface for the coagulation chemical reactions to occur. If a person’s blood clots excessively, they may develop deep vein thrombosis (DVT) and associated complications. A person can get haemophilia if their blood does not clot properly. Bleeding is far too common in this case.

Factors contributing to coagulation of blood

The thirteen coagulation factors are arranged in chronological sequence of discovery:

• Factor I: Fibrinogen
• Factor II: Prothrombin
• Factor III: Tissue thromboplastin (tissue factor)
• Factor IV: Ionised calcium ( Ca++ )
• Factor V: Labile factor or proaccelerin
• Factor VI: Unassigned
• Factor VII: Stable factor or proconvertin
• Factor VIII: Antihemophilic factor
• Factor IX: Plasma thromboplastin component (Christmas factor)
• Factor X: Stuart-Prower factor
• Factor XI: Plasma thromboplastin antecedent
• Factor XII: Hageman factor
• Factor XIII: Fibrin-stabilising factor

Mechanism of blood coagulation

The process of blood clotting or blood coagulation protects the body from blood loss or haemorrhage. The time it takes for blood to coagulate is referred to as the clotting time. It takes 3 to 5 minutes, under normal circumstances, for blood to clot.

The protein, fibrinogen, which is present in soluble form in the plasma and is converted into an insoluble network of fibrous substance fibrin by blood clotting, forms the blood clot. The four phases of blood clotting result in the synthesis of thromboplastin, thrombin, fibrin and clot.

Phase 1

This stage involves the generation of thromboplastin from injured tissue or platelets. It aids in the production of the thrombokinase enzyme.

Phase 2

In this stage, prothrombin is converted to thrombin with the help of thrombokinase and calcium ions.

Phase 3

By the action of thrombin, a soluble protein called fibrinogen in plasma is converted to an insoluble network of fibrous material called fibrin.

Phase 4

This stage witnesses the formation of a red solid mass called a blood clot, which is caused by the fibrin network trapping blood cells, primarily RBCs.

Pathways of coagulation of blood

Blood coagulation can be triggered by one of two different pathways, namely intrinsic and extrinsic pathways. 

Intrinsic pathway or contact activation pathway

Events that occur within the lumen of blood arteries can trigger the intrinsic pathway. Only elements found within or intrinsic to the vascular system (clotting factors, Ca++, platelet surface, etc.) are required for the Intrinsic pathway.

Extrinsic pathway or tissue factor pathway

The primary pathway of coagulation of blood is the extrinsic pathway. It requires tissue factor (tissue thromboplastin), a chemical that does not ordinarily circulate in the vessel and is “extrinsic to” it. When the vessel wall ruptures, the tissue factor is released.

Regardless of whether the extrinsic or Intrinsic route initiates coagulation, the process ultimately follows a common pathway. The activation of factors X, V, II, XIII, and I is part of the common pathway. Both routes are necessary for regular haemostasis. Positive feedback loops exist between them, amplifying responses to produce enough fibrin to form a lifesaving plug. The deficiency or abnormality of any one factor can impede the entire process, increasing the risk of bleeding or haemorrhage.

Disorders related to blood coagulation

Blood coagulation problems occur when the body’s ability to manage blood clotting is disrupted. These problems can lead to haemorrhage (insufficient clotting, which increases the risk of bleeding) or thrombosis (too much clotting that causes blood clots to obstruct blood flow). Several factors contribute to the development of these clotting disorders.

Haemophilia or Christmas disease or Factor IX deficiency

In this disease, the blood of the affected individual doesn’t clot by the normal process. Children suffering from haemophilia have lower levels of an essential clotting factor protein in their blood.

Von Willebrand’s disease

Von Willebrand’s disease is the most common genetic bleeding disorder. It starts to develop when the blood lacks the von Willebrand factor, which facilitates the clotting of blood.

Common symptoms of bleeding disorders

• Bruising that is inexplicable and easy to get
• Nosebleeds on a regular basis due to severe menstrual blood
• Profuse bleeding caused by minor cuts or injuries
• Leaks into the joints

Diagnosis of bleeding disorders

• Complete blood count (CBC) determines the number of red and white blood cells present in the patient’s body.
• Platelet aggregation test determines how well the patient’s platelets clump together.
• Bleeding time test determines how quickly the patient’s blood clots to avoid bleeding.

Anticoagulants

Anticoagulants are chemical substances that prevent the formation of blood clots. To prevent coagulation, an anticoagulant eliminates cations. The release of prothrombin, which is critical for blood clotting to occur, requires vitamin K. 

Dicumarol inhibits the production of prothrombin, which is required for clotting. Blood banks utilise CPD (Citrate Phosphate Dextrose), ACD (Acid Citrate Dextrose), and EDTA to keep blood samples from clotting. 

In a test tube, a small amount of oxalate or citrate can be added to prevent blood clotting (Na and K). They bind to the free Ca++ ions in blood. Hirudin is an anticoagulant that is found in leech saliva. Anophelin is found in female Anopheles saliva. 

Conclusion

The mechanism that prevents excessive blood loss from the body is called coagulation of blood or blood clotting. A clot, formed primarily of a network of threads called fibrins in which dead and ill-formed parts of blood are trapped, causes the reddish-brown muck that forms at the site of a wound. Fibrins are created when the enzyme, thrombin, converts inert fibrinogens in the blood.

Thrombins are created by an enzyme complex known as thrombokinase from another inactive material found in the blood called prothrombin. When it comes to clotting, calcium ions play a crucial role.