Haemostasis 1: Platelets Flashcards
What are the 3 main steps to stopping bleeding?
What are the names of the types of bruising here?
Bleeding into the skin due to reduced platelet count is called purpura.
- Large purpura are called ecchymoses.
- Small pinpoint sites of bleeding from capillaries are called petechiae.
How does platelet adhesion occur?
Bind to collagen or vWF via surface glycoproteins.
What are the 4 things that occur to an activated platelet?
- Shape change from disc to spheres with pseudopods.
- Granules are secreted (activates other platelets)
- Phospholipase, arachidonic acid, Cox pathway, thromboxane A2. (Trigger for more platelet aggregation).
- Glycoproteins are activated which allows for the binding of fibrin and vWF.
Is platelet activation reversible?
Yes, there is partial reversibility.
What are the 2 main granule types in platelets? What is contained in these platelets?
Dense granules and alpha granules.
How do you test nowadays for platelet function?
How does this test work?
PFA 100 (platelet function analyser).
Cartridge containing a capillary coated with activators, the time that it takes to form a platelet plug is measured.
Some drugs/foods can affect the ability of this test.
What are the precursors to platelets?
Megakaryocytes in bone marrow.
The nucleus of the megakaryocyte keeps dividing but the cell does not divide.
What is the word for lacking platelets in the blood?
Thrombocytopenia
What are the different levels of thrombocytopenia (platelet/mL) and the results?
Aspirin prolongs bleeding time by about ____ in most people. But there are……
3 minutes.
But there are hyper responders and non responders.
How does aspirin work to ‘thin’ blood?
Aspirin is a cyclooxygenase inhibitor.
TXA2 synthesis is inhibited.
Platelet activation is reduced- slower and smaller platelet plug.
How does clopidogrel work?
ADP receptor antagonist therefore inhibits platelet activation
The endothelium is resistant to platelet binding from two secreted chemicals into the blood, what are they?
Nitric oxide and prostacyclin (dilates endothelium and inhibits platelet aggregation).
What sequence of events could cause the endothelium to gain the ability to bind platelets?
Vascular injury causing vasoconstriction and expression of proteins which platelets can adhere to, activation of the platelets, more platelets.
