Thrombocytopenia: Causes and Mechanisms of Development
Thrombocytopenia is a standard pathological condition in which the number of blood platelets per unit volume falls below the physiological norm.
Various factors lead to this condition:
- Physical: high doses of ionizing radiation, which suppress platelet hemopoiesis.
- Chemical: exposure to cytostatics and alkylating agents.
- Biological: the influence of exotoxins and endotoxins from various microorganisms.
Mutations in hematopoietic stem cells, a shortage of thrombopoietin, and an excess of fibrinogen that triggers massive agglutination and aggregation also contribute to the pathology. In addition, cells can be destroyed under attack by autoaggressive immunoglobulins (Ig) or immunocytes.
The pathogenesis includes four main mechanisms:
- Suppression of the platelet lineage in the bone marrow.
- Increased destruction of circulating platelets.
- Massive consumption of cells during generalized thrombus formation (consumption thrombocytopenia).
- Excessive sequestration (pooling) in the spleen.
These processes result in a drop in platelet clotting factor activity, prolonged bleeding time, weak clot retraction, and, ultimately, the development of hemorrhagic syndrome.
Thrombocytopathies: Qualitative Defects
Thrombocytopathy represents a disorder of key platelet properties: adhesion, aggregation, and coagulation. The main difference between this condition and a quantitative deficiency is the presence of stable, long-lasting defects within the cells themselves. These changes may affect their morphology, biochemistry, or functional activity, which naturally leads to hemostatic disorders.
A symptomatic approach to treatment is used to correct the consequences (bleeding, hemorrhages, and microcirculatory disorders):
- Fluid administration: using plasma and plasma expanders to restore normal blood rheological properties.
- Stopping bleeding: performing adequate hemostatic therapy.
- Addressing post-hemorrhagic conditions: managing resulting hypovolemia, anemia, and other consequences of blood loss.
Physiology and Typical Disorders of Hemostasis
In a narrow sense, hemostasis is the process of stopping bleeding; its biological role is to prevent blood loss upon injury to blood vessels or the heart. Normally, it ensures protein coagulation, as well as the adhesion, aggregation, and activation of formed blood elements to form a blood clot.
The hemostatic system relies on three categories of mechanisms:
- Coagulation system: responsible for the coagulation of plasma proteins and the creation of a clot.
- Anticoagulant system: blocks or inhibits the coagulation process.
- Fibrinolytic system: performs lysis (dissolution) of the formed fibrin.
Coagulation is initiated via two pathways. The intrinsic pathway starts with the activation of factor XII, while the extrinsic pathway is initiated by the release of tissue factor and the activation of factor VII. Both cascades ultimately converge on a common step — the activation of factor X.
There are three groups of standard pathologies of the hemostatic system:
- Hypercoagulation (thrombotic syndrome): an inadequate, excessive increase in clotting with thrombus formation, leading to ischemia of organs and tissues. Causes may include vascular wall damage (trauma, vasculitis, atherogenesis, angiopathy) or blood cell pathologies (thrombocytopathies, enhanced erythrocyte hemolysis, hyperaggregation).
- Hypocoagulation (hemorrhagic syndrome): a pathological decrease in clotting and impaired clot formation.
- Thrombohemorrhagic syndromes: conditions characterized by phased dysfunction of the hemostatic system.