03 - Blood: platelets & haemostasis Flashcards
Define haemostasis…
The arrest of bleeding from a broken blood vessel
Platelets are anuclear (True / False)
True
Platelets are anuclear cell fragments
Contraction of the spleen triggered by the SNS releases stored…
Platelets
Platelets have a lifespan of…
7-10 days (short)
At the end of their lifespan, platelets are apoptosed and phagocytosed in the (2)…
Liver and spleen
Thrombopoetin stimulates the production of…
Megakaryoblasts
Megakaryoblasts are large cells derived from…
Repeated mitosis of the myeloid cell line without cytokinesis
Platelets have an exterior coat rich in…
Glycoproteins
The exterior coat of platelets is involved in (3)…
- Adhesion
- Aggregation
- Activation
Platelets contain 2 types of granule…
- Alpha
* Delta (dense)
Alpha granules contain…
Clotting mediators
Factors V, VIII; VWF; fibrinogen
Dense granules contain…
ADP, Ca2+ and Seratonin
Low platelet count is known as…
Thrombocytopenia
Thrombocytopenia may be caused by…
Autoimmunity or drugs
Thrombotic thrombocytopenic purpura is a rare condition in which…
Small clots reduce platelet numbers
The first step in the process of haemostasis is…
Vascular spasm
Describe the events of vascular spasm (haemostasis step 1)…
Release of 5HT and ADP from damaged cells and platelets leads to constriciton of smooth muscle. This reduces blood flow and pushes together endothelial cuts which have become sticky
Step 2 in haemostasis is…
Platelet plug formation
Von Willebrand Factor (VWF) activates…
Platelets
Platelet factors attract platelets to the site of the damage, which aggregate to form a…
Plug
The plug formed in step 2 of haemostasis is sealed by (3)…
- Compaction
- Further vasoconstriction
- Clotting cascade
Step 3 in haemostasis is…
Coagulation (blood clotting)
The blood clot strengthens and supports…
The plug
Clotting steps (2)…
- Fibrinogen is converted to fibrin by thrombin (Factor IIa protease)
- Fibrin (monomer) is polymerised by Ca2+ and Factor VIIIa
