Haematology II - Lecture 9

Question 1

What are platelets?

Answer 1

○ Small, oval, no nucleus
○ 2-3um diameter
○ Contain granules: have clotting factors

Question 2

How are platelets formed?

Answer 2

From the megakaryocyte cytoplasm where one megakaryocyte can produce 4,000 platelets

Question 3

What regulates the production of platelets?

Answer 3

○ No. of circulating platelets: negative feedback
○ Thrombopoietin release: increase platelet numbers

Question 4

What is the lifespan of platelets?

Answer 4

7-10 days

Question 5

What causes vasoconstriction?

Answer 5

○ Vessel injury: reflex to reduce blood flow
○ Serotonin: released from platelet activation
○ Thromboxane: released from platelet activation

Question 6

What happens with the platelets when a vessel is injured?

Answer 6

○ 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

Question 7

What initiates coagulation?

Answer 7

Tissue factor (Factor III)

Question 8

What happens in the extrinsic pathway of coagulation?

Answer 8

○ 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

Question 9

What happens in the intrinsic pathway of coagulation?

Answer 9

○ 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

Question 10

What happens in common pathway of coagulation?

Answer 10

○ Factor X -> Prothrombinase: consists of FXa and FVa as a co-factor
○ Prothrombinase -> Thrombin
○ Thrombin converts fibrinogen to fibrin

Question 11

What affects coagulation?

Answer 11

○ Ca2+: low concentration will impair blood clotting
○ Vitamin K: necessary for production of certain clotting factors e.g. prothrombin

Question 12

What controls clotting?

Answer 12

○ Antithrombin: inhibits thrombin
○ Heparin: released by basophils and mast cell - co-factor that accelerates actions of antithrombin

Question 13

What is fibrinolysis?

Answer 13

Fibrin clot is broken down

Question 14

What is the main enzyme in fibrinolysis?

Answer 14

○ Plasmin
○ Plasminogen is converted to plasmin
○ Produce fibrin degradation products

Question 15

What does A blood group contain?

Answer 15

○ A antigens
○ Anti-B antibodies

Question 16

What does B blood group contain?

Answer 16

○ B antigens
○ Anti-A antibodies

Question 17

What does AB blood group contain?

Answer 17

○ A antigens
○ B antigens
○ No antibodies

Question 18

What does O blood group contain?

Answer 18

○ No antigens
○ Anti-B antibodies
○ Anti-A antibodies

Question 19

What is agglutination and hemolysis?

Answer 19

○ Agglutination: antibodies recognise antigens on foreign red blood cells and clump them together
○ Hemolysis: break down of red blood cells

Question 20

What is the Rh blood group?

Answer 20

○ Either Rh negative or Rh positive
○ Rh negative will not usually contain anti-Rh antibodies
○ Requires sensitisation by exposure to Rh+ RBCs

Question 21

What causes Rh- blood to make anti-Rh antibodies?

Answer 21

○ Transfusion of the wrong blood type
○ Preganancy/birth: Rh- mother and Rh+ baby

Question 22

What is haemolytic disease and how it it caused?

Answer 22

○ 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)

Question 23

What treatment is there to prevent haemolytic disease?

Answer 23

Anti-D: prevents immune reaction