PSL201Y1 Chapter Notes - Chapter 15: Von Willebrand Factor, Factor X, Hemostasis
Document Summary
Platelets are colourless cell fragments that arise when portions of large bone-marrow cells called megakaryocytes break off. Hemostasis is the mechanism in the body that stops bleeding. Increases resistance to blood flow, minimizes loss at damaged area. Platelets possess granules containing substances that can be secreted into plasma (ex. Key protein is von willebrand factor (vwf): secreted by megakaryocytes, platelets, and endothelial cells lining blood vessels: step 1: platelet adhesion when blood vessel damage exposes tissue underlying endothelium (subendothelial tissue) When blood contacts subendothelial tissue, vwf binds to collagen fibre and platelets bind to vwf, anchoring the plug: step 2: platelet aggregation caused by adp secreted by activated platelets; adp secretes thromboxane which helps aggregation. Positive feedback loop of platelet adp/thromboxane secretion and aggregation. Do not form on normal endothelium b/c healthy endothelial cells secrete nitric oxide and prostacyclin which inhibit platelet aggregation. Contractile proteins actin and myosin tighten the plug structure.
