Haemostasis

Haemostasis

Haemostasis is the normal physiological response that prevents significant blood loss following vascular injury. The process depends on an intricate series of events involving platelets, other cells and the activation of specific blood proteins, known as coagulation factors. When blood vessel injury occurs, physiological haemostasis is triggered and the coagulation process occurs. Haemostasis serves to maintain the integrity of the circulatory system; however the process can become imbalanced, leading to significant morbidity and mortality. Knowledge of the process of haemostasis is therefore important in order to understand the major disease states associated with thrombosis.


Blood Clot Formation - Coagulation Factors & Platelets

Blood Clot Formation - Coagulation Factors & Platelets

About blood clot formation. Clot formation is the process by which blood forms clots, it's an important part of haemostasis. Coagulation (thrombogenesis) is the process by which blood forms clots.

About blood clot formation. Clot formation is the process by which blood forms clots, it's an important part of haemostasis. Coagulation (thrombogenesis) is the process by which blood forms clots.


The coagulation cascade

The coagulation process that leads to haemostasis involves a complex set of protease reactions involving approximately 30 different proteins. These reactions convert fibrinogen to fibrin, which, together with platelets, form a stable thrombus. Several coagulation cascade models have been proposed, including the intrinsic and extrinsic pathway model and the more recent cell-based model. Building on these models, ongoing research has elucidated other components of the coagulation process including microparticles and the protein P-selectin. An inherited or acquired imbalance in the coagulation system that leads to an increased risk of thrombosis is called thrombophilia. Approximately one in three patients with venous thromboembolism (VTE) has an inherited thrombophilia.


Fatal Pulmonary Embolism

This post-mortem exam shows a fresh pulmonary embolus in a major pulmonary artery. The lethality of a pulmonary embolus is not dependent on size alone but rather the underlying cardiovascular condition of the patient.

This post-mortem exam shows a fresh pulmonary embolus in a major pulmonary artery. The lethality of a pulmonary embolus is not dependent on size alone but rather the underlying cardiovascular condition of the patient.

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Venous Thrombi

Formation of a thrombus within a vein is known as a venous thrombosis. If the thrombus breaks loose and travels through the blood system, it is known as an embolus. Venous thrombi manifest as deep vein thrombosis (DVT) and pulmonary embolism (PE). DVT is the most common type of venous thromboembolism (VTE) but patients with DVT are also at risk of PE, which can potentially be life-threatening. VTE is associated with cancer, trauma and surgery and several pre-disposing risk factors, including pregnancy, obesity and immobility, have been identified. VTE can also lead to serious long-term complications, including post-thrombotic syndrome (PTS) and chronic thromboembolic pulmonary hypertension (CTPH).


Coagulation Cascade Animation - Physiology of Hemostasis

Coagulation Cascade Animation - Physiology of Hemostasis

Coagulation Cascade: description of the physiological process of hemostasis including platelet plug formation and about the intrinsic and extrinsic pathways.

Coagulation Cascade: description of the physiological process of hemostasis including platelet plug formation and about the intrinsic and extrinsic pathways.


Thrombus Formation

Haemostasis is necessary for survival, but the pathological formation of a thrombus poses significant health risks. A pathological thrombus, formed when there is an imbalance in the blood coagulation system, can potentially obstruct blood flow, leading to a number of serious health conditions. Two different types of thrombi can be formed: arterial thrombi and venous thrombi. The pathologist Rudolph Virchow postulated that thrombus formation and propagation resulted from abnormalities in three areas, collectively known as Virchow’s Triad. Clinicians can now quantify some of these factors that, when abnormal, are associated with an increased risk of venous thromboembolism (VTE) and other cardiovascular diseases and of stroke in patients with atrial fibrillation (AF).


Arterial Thrombosis

When a thrombus forms within an artery, this is known as an arterial thrombosis. Arterial thrombi manifest as Myocardial Infarction (MI), unstable angina, ischaemic stroke and some manifestations of peripheral arterial disease, such as acute limb ischaemia. Risk factors for arterial thrombosis include smoking; obesity; high blood pressure; increasing age; and family history. The incidence and prevalence of the clinical manifestations of arterial thrombosis is high. The annual incidence of MI and stroke in the US in 2008 has been calculated to be 935,000 and 795,000, respectively.