Haemostasis Flashcards
Define Hemostasis
A multi stage process that transforms blood into a semisolid clot to prevent further blood loss
What are the three stages of Hemeostasis
- Vascular spasm
- Platelet aggretation
- Clotting cascade
Define Haemocrit and its % breakdown
- Amount of red blood cells
Plasma 55%
White Blood cells 1%
Red blood cells 45%
What is normal level of Haemorit in men and woman
Men 40-54%
Woman 36-48%
Normal level for Haemoglobin for men and woman
Male - 14-18gd/l
Woman - 12 - 16 gd/l
Normal INR levels
0.8 - 1.1
If on warfarin normal is 2.0-3.0
Define platelet aggregation
- Damaged vessel wall has a inflammatory response and expose proteins within the vessel walls, these are collagen and elastin fibres which when expose causes platelets to attach themselves to the damaged vessel wall. During the build up platelets release thromboxane which increase the cells ability to stick together and causes vasoconstriction.
Define Vascular spasm
- When a vessel is damaged it constricts to stop any bleed, it also reduces the blood flow to the smaller vessels, the blood flow through is now reduced which increases the likelihood of the platelets and plasma to come into contact with the damaged area
What does Extrinsic pathway mean
When the vessels have been damaged from the outside usually by trauma
What does Intrinsic mean
Begins in the bloodstream and is triggered by internal damage to the wall of the vessel.
Explain the Extrinsic pathway to clotting
extrinsic pathway (also known as the tissue factor pathway) begins when damage occurs to the surrounding tissues, such as in a traumatic injury. Upon contact with blood plasma, the damaged extravascular cells, which are extrinsic to the bloodstream, release factor III (thromboplastin). Sequentially, Ca2+ then factor VII (proconvertin), which is activated by factor III, are added, forming an enzyme complex. This enzyme complex leads to activation of factor X (Stuart–Prower factor), which activates the common pathway discussed below. The events in the extrinsic pathway are completed in a matter of seconds.
Explain the Intrinsic pathway to clotting
The intrinsic pathway is most often initiated when factor XII (Hageman factor). Within the body, factor XII is typically activated when it encounters negatively charged molecules, such as inorganic polymers and phosphate produced earlier in the series of intrinsic pathway reactions. Factor XII sets off a series of reactions that in turn activates factor XI (antihemolytic factor C or plasma thromboplastin antecedent) then factor IX (antihemolytic factor B or plasma thromboplasmin). In the meantime, chemicals released by the platelets increase the rate of these activation reactions. Finally, factor VIII (antihemolytic factor A) from the platelets and endothelial cells combines with factor IX (antihemolytic factor B or plasma thromboplasmin) to form an enzyme complex that activates factor X (Stuart–Prower factor or thrombokinase), leading to the common pathway. The events in the intrinsic pathway are completed in a few minutes.
Explain the common pathway to clotting
Both the intrinsic and extrinsic pathways lead to the common pathway, in which fibrin is produced to seal off the vessel. Once factor X has been activated by either the intrinsic or extrinsic pathway, the enzyme prothrombinase converts factor II, the inactive enzyme prothrombin, into the active enzyme thrombin. (Note that if the enzyme thrombin were not normally in an inactive form, clots would form spontaneously, a condition not consistent with life.) Then, thrombin converts factor I, the insoluble fibrinogen, into the soluble fibrin protein strands. Factor XIII then stabilizes the fibrin clot.
What is the function and need for Fibrinolysis
To restore normal blood flow as the vessel heals, the clot must eventually be removed. Fibrinolysis is the gradual degradation of the clot.During this process, the inactive protein plasminogen is converted into the active plasmin, which gradually breaks down the fibrin of the clot. Additionally, bradykinin, a vasodilator, is released,
What effect does Heperin have on the clotting cascade
- Heperin = Leads to a anticoagulation of the blood by activating antithrombin 3, which stops the cascade at thrombin stage.
