769363
Description
Flashcards by sophietevans, updated more than 1 year ago
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Created by sophietevans
over 10 years ago
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| Question | Answer |
| Platelets are not technically part of the immune system - which system are they part of? How could they be said to be part of the immune system? | Platelets are not really part of the immune system, as their function lies in haemostasis. However, this could be extrapolated in that haemostasis prevents blood loss but also entrance of pathogens as a wound is closed off. |
| What size are platelets? | 2μm |
| Which cells are platelets derived from? | They are cytoplasmic fragments produced by megakaryocytes in the bone marrow. |
| What is the lifespan of platelets in the peripheral circulation? | 8-12 days |
| What are the two types of granules that platelets contain? | Alpha granules and dense granules. |
| What is contained in the alpha granules of platelets? | Alpha granule contents: fibrinogen, von Willebrand factor, thrombospondin, platelet-derived growth factor, fibronectin, platelet factor 4 (an anti-heparin) |
| What is contained in the dense granules of platelets? | Dense granule contents: ADP/ATP, calcium, histamine, adrenaline, serotonin |
| What attracts platelets to a wound? | Exposed subendothelial connective tissue of a vessel. |
| What does the adherence of platelets to the subendothelial connective tissue form? | The primary haemostatic plug. |
| Three surface membrane receptors on platelets are critical for their adherence in the formation of the primary haemostatic plug. What are these and what do they bind to? | • gpIa/IIa binds to collagen • gpIb/IX binds to von Willebrand's factor • gpIIb/IIIa binds to fibrinogen and von Willebrand's factor |
| When might a primary haemostatic plug be sufficient on its own? | In minimal damage to microvasculature. |
| What does the secondary haemostatic plug form as a result of? | Platelets releasing their granule contents and activating the coagulation pathway and causing platelet aggregation. |
| Which chemicals are released from dense bodies which are important in the coagulation cascade and platelet aggregation? | Ca2+ and ADP. |
| Which receptor is expressed on platelets once they are activated that is critical in their adhesion? | The gpIIb/IIIa receptor is expressed, which binds fibrinogen and bridges adjacent platelets. |
| What shape are platelets before activation? What intracellular molecules/structures maintain this? | Before activation, platelets are disc shaped (a conformation maintained by microtubules, and actin and myosin filaments at the periphery). |
| What happens to platelet structure on activation? | Platelets turn themselves inside out using their open canalicular system and become spheroid with long pseudopods that spread over the damaged surface. |
| How does the platelet plug contract? | After aggregation, the internal filaments (actin and myosin) slide so that the platelet plug contracts to stabilise and anchor it. |
| What converts fibrinogen to fibrin to stabilise the secondary haemostatic plug and also further enhances platelet activity? | Thrombin |
| Which vasodilator do platelets produce? | Serotonin |
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