Haematology II - Lecture 9 Flashcards
What are platelets?
○ Small, oval, no nucleus
○ 2-3um diameter
○ Contain granules: have clotting factors
How are platelets formed?
From the megakaryocyte cytoplasm where one megakaryocyte can produce 4,000 platelets
What regulates the production of platelets?
○ No. of circulating platelets: negative feedback
○ Thrombopoietin release: increase platelet numbers
What is the lifespan of platelets?
7-10 days
What causes vasoconstriction?
○ Vessel injury: reflex to reduce blood flow
○ Serotonin: released from platelet activation
○ Thromboxane: released from platelet activation
What happens with the platelets when a vessel is injured?
○ Platelet adhesion: sticks to the damaged surface
○ Platelet activation: change their shape, granule secretion and activation of glycoproteins
○ Platelet aggregation: Forms the primary haemostatic plug which are a layer of platelets
What initiates coagulation?
Tissue factor (Factor III)
What happens in the extrinsic pathway of coagulation?
○ Tissue factor binds to clotting factor VII (7)
○ Forms tissue factor-FVIIa complex
○ Binds to FX and activates it to become FXa
○ Fast and efficient and is 90% responsible for the production of fibrin clot
What happens in the intrinsic pathway of coagulation?
○ Factor XII (12) to XIIa
○ Factor XIIa activates factor XI (11) to XIa
○ FactorXIa activates FIX (9) to IXa
○ Factor IXa and co-factor VIII (8) form the factor X activator complex
○ Activates Factor X
○ Slow but sustained
What happens in common pathway of coagulation?
○ Factor X -> Prothrombinase: consists of FXa and FVa as a co-factor
○ Prothrombinase -> Thrombin
○ Thrombin converts fibrinogen to fibrin
What affects coagulation?
○ Ca2+: low concentration will impair blood clotting
○ Vitamin K: necessary for production of certain clotting factors e.g. prothrombin
What controls clotting?
○ Antithrombin: inhibits thrombin
○ Heparin: released by basophils and mast cell - co-factor that accelerates actions of antithrombin
What is fibrinolysis?
Fibrin clot is broken down
What is the main enzyme in fibrinolysis?
○ Plasmin
○ Plasminogen is converted to plasmin
○ Produce fibrin degradation products
What does A blood group contain?
○ A antigens
○ Anti-B antibodies
What does B blood group contain?
○ B antigens
○ Anti-A antibodies
What does AB blood group contain?
○ A antigens
○ B antigens
○ No antibodies
What does O blood group contain?
○ No antigens
○ Anti-B antibodies
○ Anti-A antibodies
What is agglutination and hemolysis?
○ Agglutination: antibodies recognise antigens on foreign red blood cells and clump them together
○ Hemolysis: break down of red blood cells
What is the Rh blood group?
○ Either Rh negative or Rh positive
○ Rh negative will not usually contain anti-Rh antibodies
○ Requires sensitisation by exposure to Rh+ RBCs
What causes Rh- blood to make anti-Rh antibodies?
○ Transfusion of the wrong blood type
○ Preganancy/birth: Rh- mother and Rh+ baby
What is haemolytic disease and how it it caused?
○ Rh- mother and Rh+ baby
○ Mother’s blood and fetal’s blood are usually separate during pregnancy
○ At delivery: mixing of blood and mom has an immune response and begins producing anti-Rh antibodies (takes 72 hours)
○ Antibodies remain in mother’s circulation
○ If the mother gets pregnant again: antibodies can cross in the fetal tissue and destroy their RBCs leading to death (haemolysis)
What treatment is there to prevent haemolytic disease?
Anti-D: prevents immune reaction
