Porth's Essentials of Pathophysiology, 4e

emostasis is a multistep process that maintains the integrity of a closed high-pressure circulatory system after vessel injury. The normal process of hemostasis is regulated by a complex array of activators and inhibi- tors that maintain blood fluidity and prevent blood from leaving the vascular compartment. Hemostasis is normal when a blood vessel is sealed to prevent blood loss and hemorrhage. It is deemed abnormal when inappropriate blood clotting occurs or when clotting is insufficient to stop the flow of blood from the vascular compartment. Disorders of hemostasis fall into two main categories: the inappropriate formation of clots within the vascular system (thrombosis) and the failure of blood to clot in response to an appropriate stimulus (bleeding). H Disorders of Hemostasis 12 C h a p t e r Hemostasis preserves vascular integrity by balancing the processes that maintain blood in a fluid state and prevent excessive bleeding following injury. The process involves the transformation of blood into a semisolid clot with erythrocytes trapped in its fibrin meshwork at the site of injury (Fig. 12-1). Components of Hemostasis Hemostasis is a multistep process that involves platelets, plasma clotting factors, naturally occurring anticoagu- lants, and the inherent properties of the endothelial lin- ing of blood vessels. Platelets Platelets, also called thrombocytes, are large fragments from the cytoplasm of bone marrow cells called mega- karyocytes. 1–5 There are normally 150,000 to 400,000 platelets in each microliter ( μ L) of blood 1 with an aver- age platelet life span of 8 to 9 days. Platelets do not leave the blood as white blood cells do, but at any time about one third of them are stored in blood-filled spaces in the spleen and can be released into the circulation as needed. Platelet production is controlled by a protein Hemostasis and Blood Coagulation

Hemostasis and Blood Coagulation Components of Hemostasis Platelets The Coagulation System Endothelium Clot Formation and Dissolution Vessel Spasm Platelet Plug Formation The Coagulation Cascade

Clot Retraction Clot Dissolution Hypercoagulability States

Increased Platelet Function Increased Clotting Activity

Inherited Disorders Acquired Disorders

Bleeding Disorders Platelet Disorders

Thrombocytopenia Impaired Platelet Function

Coagulation Disorders Inherited Disorders Acquired Disorders Bleeding Associated with Vascular Disorders Disseminated Intravascular Coagulation

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