OR the tollowing flow chart, fill in the four (4) blanks in the process of clot

Question

OR the tollowing flow chart, fill in the four (4) blanks in the process of clot formation and dissolution. Add to the chart where COX inhibitors and t-PA's would exert there effects. Use an arrow to indicate the precise location. Use your lecture notes and Fig. 16-8 in Silverthorn. (6 pts) . a) Why would t-PA's NOT be given to a patient that suffered from a hemorrhagic stroke? (1 pt). Which drug, COX inhibitors or t-PA's is used prophylactically to prevent formation of clots? (1pt) b) Cell growth and c) How does the anti-coagulant heparin prevent blood from clotting? Label on the diagram, where heparin would exert it's effects (2 pts). Copyight02009 Peason Education Inc

Explanation / Answer

1] *The topmost box -- exposed collagen fibers on vessels

*  The box below it -- activated factors secrete chemicals, serotonin, and thromboxane.

* The box on the right -- thrombin converts fibrinogen, which is a soluble protein, into long insoluble proteins called fibrin.

* The lowermost box -- the mesh formed by fibrins traps erythrocytes and platelets, pulls the edges of the broken blood vessel together and stops bleeding.

a] t-PA or tissue plasminogen activator is a protein involved in the breakdown of blood clots. It is a serine protease found on endothelial cells which line the blood vessels. It is a systemic thrombolytic [clot cissolving] agent and is used in the treatment of heart attack and strokes. Despite its efficacy, t-PAs are not given to patients suffering from hemorrhagic strokes because it can lead to intracranial hemorrhages which are fatal for life. It affects the neurovascular unit and the brain parenchyma.

b] The enzymes that produce prostglandins are called cyclo-oxygenase [COX]. They are of two types- COX-1 and COX-2. Both these enzymes produce prostglandins that promote inflammation, pain, and fever. COX-1 additionally, produces prostaglandins that activate platelets and protects the stomach and intestinal lining.

Anti-inflammatory drugs such as aspirin, ibuprofen etc block the action of COX and help reduce inflammation, but they may also decrease the natural protective mucus lining of the stomach and intestine, leading to ulcers and bleeding. However, these drugs also act as blood 'thinners'.

So, COX inhibitors are generally used prophylactically to prevent clot formation in the blood.

t-PAs are used to dissolve the clots.

c] Heparin is an anticoagulant that is used to prevent blood from clotting. Heparin works by preventing thrombin and prothrombin from working correctly. It produces its anticoagulant effect by inactivating thrombin and activated factor X through an anti thrombin-dependent mechanism. Heparin binds to AT through high-affinity Penta saccharides. For inhibition of thrombin, heparin must bind to both the coagulation enzyme and AT.

So, thrombin will act by disrupting the function of thrombin so that the further steps of blood clotting cannot proceed.

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