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Unformatted text preview: MT 204 Exam 3 Upon completion of the section on thrombosis, the participant should be able to: 1. Compare and contrast clots and thrombi in terms of origin and the hemostatic system involved. A thrombus is a solid mass or plug formed within the heart, arteries, veins, or capillaries from the components of the streaming blood. The process involves both platelet activation and clotting, the mechanisms being identical to those occurring in haemostasis. In clotting the activation of a protein cascade system within the blood vessels leads to the generation of thrombin and thus to the conversion of soluble fibrinogen to insoluble fibrin. 2. The four contributions of platelets to hemostasis. 1. Adhere to underlying vessel wall 2. Release of pharmacologically active compounds 3. Aggregate to form plug (platelet to platelet interaction and adherence) 4. Provide co-factors for clotting 3. Detail the actions of adhesion, release, aggregation and interaction with the clotting system that platelets provide to hemostasis including the result if any of the processes or integral components or process are lacking Adhesion – platelets adhere to damaged endothelial cells or exposed subendothelial tissues when vessel wall-derived ligands bind to glycoprotein receptors on the platelets. Collagen, which is exposed when a vessel is damaged, binds to a glycoprotein receptor (GPIa)-platelet. Von Willebrand factor (vWf) binds to a glycoprotein (GPIb)- endothelium. Deficiencies of GPIa or GPIb cause bleeding defects. Release – Adherent platelets change shape and release several pre-formed and newly formed molecules which may affect both haemostasis and the metabolism of the underlying vessel wall. Platelets contain two types of storage granules, alpha granules (PDGF, thrombospondin, platelet factor 4, fibrinogen, fibronectin, vWF) and dense bodies (ATP, ADP, GDP, GTP, serotonin, calcium). Also, there is the release of archidonate which is the first step in the synthesis of prostaglandins that both promote and prevent aggregation. Aggregation – Platelets form a mass through the agency of fibrinogen bridges between adjacent platelets. Fibrinogen binds to receptors formed by a rearrangement of two platelet surface glycoproteins, GPIIb and IIIa, which are integrins. This receptor also binds to vWf and may thus make a contribution to platelet adhesion as well. The stimuli for aggregation are ADP and thromboxane A2. Provision of co-factors for clotting – Platelets interact with clotting cascade proteins such as factors V, VIII, IX, and X. Following activation, phospholipids that are normally present on the internal layer of their plasma membranes are flipped to the external aspect of the cell....
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- Spring '08
- host cell, Platelet, alpha granules