Blood Clotting 27/09 Flashcards
Describe vasoconstriction?
When there is an injury to blood vessels vasoconstriction occurs. It is the most immediate protection against blood loss and the effect only lasts a few seconds.
What are platelets?
They make up megakaryocytic cytoplasm and In one megakaryocyte there are 4000 platelets. 2-4Um diameter they contain granules and have a lifespan of 7-10 days.
What controls the production of platelets?
-Number of circulating platelets (negative feedback) and the thrombopoitein release which increase platelet number. (TPO).
Describe platelet plug formation? (Primary haemostasis).
1) Adhesion (platelets come into contact with collagen)
2) Secretion/ Release (stimulates the release of Adenosine diphosphate)
3) Activates the platelet
4) Promotes further adhesion via positive feedback (more ADP and thromboxane A2)
5) Induces aggregation
How does vasoconstriction also occur as well as the platelet plug?
Platelet activation, release, adhesion and aggregation causes the release of granule contents, releasing ADP and serotonin. Serotonin induces vasoconstriction. Platelet membrane changes caused by the platelet plug also releases Thromboxane A2 negative feedback causing more clotting.
Describe the coagulation phase? (Secondary haemostats).
Secondary hemostasis includes the two main coagulation pathways, intrinsic and extrinsic, that meet up at a point to form the common pathway. The common pathway ultimately activates fibrinogen into fibrin. These fibrin subunits have an affinity for each other and combine into fibrin strands that bind the platelets together, stabilizing the platelet plug
What significace do vitamin K and calcium have on clotting processes?
-They affect almost every aspect of the clotting process. Any disorder that decreases Ca2+ concentration will impair blood clotting. Adequate vitamin K is necessary for production of certain clotting factors in the liver including prothrombin.
Describe physiological changes in pregnancy affecting clotting?
-Pregnancy affects coagulation and fibrinolysis. Many clotting factors increase and inhibitors decrease so increased clotting and decrease fibrinolysis is possible.
What are the two venous thromboembolism risks in pregnancy?
Comprises of deep vein thrombosis and pulmonary embolism.
When are venous thromboembolisms most common?
Puerperium (6 weeks postnatal). Pulmonary embolism is the lead cause of maternal death in the western world.
Why use heparin and not warfarin in pregnancy?
Crosses placenta
– may cause bleeding in the fetus
– Is a teratogen, causes birth defects especially embryopathy in the first trimester
