Leukocyte Disorders • Leukopenia • Abnormally low WBC count: drug induced by glucocorticoids or chemo • Leukemias • Abnormally high WBC count • Cancerous conditions involving WBCs Platelets • Small fragments of megakaryocytes • Formation is regulated by thrombopoietin produced by liver and kidney • Form a temporary platelet plug that helps seal breaks in blood vessels • Circulating platelets are kept inactive and mobile by NO and prostacyclin from endothelial cells of blood vessels Hemostasis: pathway to stop the bleeding of a damaged blood vessel 1 st step: Vascular Spasm 6/1/2018 Page 6
BIO 202IN: Human Anatomy and Physiology II • Vasoconstriction of the damaged blood vessel o Caused by smooth muscle in the wall of the blood vessel contracting • Triggered by: • Direct injury to vascular smooth muscle • Chemicals released by endothelial cells and platelets 2 nd Step: Platelet Plug Formation • At site of blood vessel injury: Platelets stick to exposed collagen fibers Swell, and become sticky, and release chemicals which attract more platelets This is a positive feedback cycle that continues until the hole is plugged 3 rd Step: Coagulation *0 Formation of a clot *1 Prothrombin is converted to thrombin *2 Thrombin is an enzyme that converts fibrinogen to fibrin. *3 Platelet plug is reinforced with fibrin threads which traps platelets, RBCs and plasma • Coagulation Phase is triggered by tissue-damaging events • Circulating clotting factors are activated • Calcium is required • Intrinsic pathway • Activated by factors present within the blood, like activated platelets • Extrinsic pathway • Activated by exposure to tissue factor (TF) from tissues outside the blood • Bypasses several steps of the intrinsic pathway, so is faster Clot Retraction *0 Platelets pull on the fibrin strands, squeezing serum from the clot *1 Serum is plasma minus fibrinogen and clotting factors Clot Repair *2 Platelet-derived growth factor stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall *3 Vascular endothelial growth factor stimulates endothelial cells to multiply and restore the endothelial lining Fibrinolysis: Removal of unneeded clots by plasmin (a fibrin-digesting) after healing has taken place Clot Formation Limited by: • Smoothness and structure of endothelial lining of blood vessels • Swift removal and dilution of clotting factors caused by rapidly moving blood • Anticoagulants remove thrombin Most thrombin gets bound to fibrin Antithrombin III and heparin inactivate circulating thrombin and other procoagulants Thromboembolytic Conditions • Thrombus : clot that develops and persists in an unbroken blood vessel 6/1/2018 Page 7
BIO 202IN: Human Anatomy and Physiology II • Deep vein thrombosis • May block circulation, leading to tissue death • Embolus : a thrombus freely floating in the blood stream • An embolism blocks a blood vessel •
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