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Harrison's Principles of Internal Medicine, 18e
| Part 7. Oncology and Hematology > Section 3. Disorders of Hemostasis > |
Chapter 115. Disorders of Platelets and Vessel Wall
Sections: Disorders of Platelets and Vessel Wall: Introduction, Disorders of Platelets, Disorders of the Vessel Wall, Acknowledgment, Further Readings.
Topics Discussed: platelet abnormalities; wall of blood vessel.
Excerpt:"Hemostasis is a dynamic process in which the platelet and the blood vessel wall play key roles. Platelets become activated upon adhesion to von Willebrand factor (VWF) and collagen in the exposed subendothelium after injury. Platelet activation is also mediated through shear forces imposed by blood flow itself, particularly in areas where the vessel wall is diseased, and is also affected by the inflammatory state of the endothelium. The activated platelet surface provides the major physiologic site for coagulation factor activation, which results in further platelet activation and fibrin formation. Genetic and acquired influences on the platelet and vessel wall, as well as on the coagulation and fibrinolytic systems, determine whether normal hemostasis, or bleeding or clotting symptoms, will result.Platelets are released from the megakaryocyte, likely under the influence of flow in the capillary sinuses. The normal blood platelet count is 150,000–450,000/ L. The major regulator of platelet production is the hormone thrombopoietin (TPO), which is synthesized in the liver. Synthesis is increased with inflammation and specifically by interleukin 6. TPO binds to its receptor on platelets and megakaryocytes, by which..."
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