Platelets Flashcards
what is the function of platelets?
haemostasis
- formation of blood clots
what is the lifespan of platelets?
7-10 days
where are platelets located?
70% bloodstream
30% spleen
what do platelets originate from?
megakaryocytes (bone marrow)
why are platelets not true cells?
- no nucleus
- no nuclear DNA
what are the types of granules in platelets?
alpha-granules
dense granules
which type of granules in platelets have a high molecular weight?
alpha-granules
what types of surface receptors do platelets have?
- agaonist
- adhesion
what is the function of agonist receptors?
stimulatory molecules
what is the function of adhesion receptors?
adhesion of platelets to:
- other platelets
- vessel walls
- leucocytes
what are the main stages of formation of blood clots?
- adhesion
- activation
- aggregation
Describe adhesion of platelets
- Injury to blood vessel wall exposes underlying endothelium and collagen fibres
- Damaged endothelium releases vWF
- vWF binds to collagen
- vWF and collagen bind to receptors on platelets
- Collagen triggers clotting cascade
- Tissue factors in blood generate thrombin
- Thrombin converts fibrinogen to insoluble fibrin
- Fibrin net captures platelets to form platelet plug
Describe activation of platelets
- Platelet binds to collagen
- Glycoprotein IIb/IIIa pathway activated
- ADP and thromboxane A2 produced
- Activates other platelets
What does platelet activation result in?
morphological change on membrane surface
- increases SA
- prepares for aggregation
describe aggregation of platelets
- once activated, platelets express GP IIb/IIIa receptor
- receptor binds with vWF / fibrinogen
- fibrinogen facilitates formation of crosslinks between platelets
- aids platelet aggregation to form platelet plug
