10 Haematology III - Transfusions and platelets Flashcards
How many systems are there for classifying blood?
35
What is the most clinically relevant blood categorisation system?
ABO
Rh(D)
What are the different blood groups?
A
AB
B
O
What determines your blood group?
Genetics
the antigens on your RBCS
Which antigens do A blood people have?
A
Which antigens do B blood people have?
B
Which antigens do AB blood people have?
Both
Which antigens do O blood people have?
neither
Which antibodies do A people have?
Anti B
Which antibodies do B people have?
Anti A
Which antibodies do AB people have?
none
Which antibodies do O people have?
anti a and anti b
What happens if you are transfused the wrong tyoe of blood?
The anti whatever antibodies detect the RBCs as foreign cells and cause agglutination which then causes blood cells to be broken down (hemolysis) and arteries can be blocked
It can be fatal.
What antigens do you have if you are Rh(D) positive? what proportion of the population?
D
85%
What antigens do you have if you are Rh(D) negative? what proportion of the population?
Just your A or B ones
15%
What antibodies do you have if you are Rh(D) positive?
none
What antibodies do you have if you are Rh(D) negative?
none - unless you have been exposed to Rh- blood in the past in which cases you have anti Rh(D) -this is a problem in pregnant women with Rh+ babies because the blood can mix during child birth and in the second child this will cause her blood to attack her babies blood
What are the elements of haemostasis?
- vasoconstriction
- platelet adhesion and aggregation
- clotting - coagulation phase
What is the balance we need to strike in haemostasis
we need a balance between excessive bleeding and clotting (know when to break the clot down)
platelet structure:
- 2-3 micrometers in diameter (size of smallest blood vessels)
- no nucleus
- lifespan 7-10 days
- oval
- very small
- contain granules
what does the release of granules in platelets do?
allows agglutination and adhesion
Where cells are platelets made from?
Megakaryocytes
What is the production of platelets controlled by?
- no of. circulating platelets (-ve feedback)
- thrombopoietin release (increases number of platelets)
What happens when a blood vessel gets damaged? (not waterfall)
- vasoconstriction
- platelets activated by exposed collagen fibres in damaged endothelium
- platelets aggregate and adhere to colagen fibres
- adhesion causes them to change shape and release granular contents
- release 5-HT (vasoconstrictor)
- release ADP (activates more platelets and causes them to release more granular contents)
- When the platelet membrane changes shape it develops pseudopodia and gets bigger so it can aggregate better with other platelets
- Also releases Platelet Factor 3 (coagulant) and thomboxane A2 which activates platelets more and causes vasoconstriction
- through all this you get the formation of the temporary platelet
What happens in the coagulation phase of haemostasis?
-Soluble plasma protein fibrinogen is converted to insoluble rigid polymer fibrin
What is used in forming the stable clot?
- fibrinogen –> fibrin
- thrombin (enzyme) ^^
- clotting factor 13 stabilises fibrin
What happens in clotting? extrinsic pathway /initiation phase
tissue damage –> tissue factor released into blood stream –> combines with factor VII (7) and activates it = tissue factor-factor VIIa complex (a means activated)
this activates factor X –> Factor Xa (X=10)
-happens within seconds
Which process produces more Factor Xa? intrinsic or extrinsic?
Intrinsic (90% more even though its slower)
What happens in clotting? intrinsic pathway
Clotting Factor VIIII gets involved - its cofactor VIII helps speed thing up and they activate Factor X
What happens in clotting? common pathway
Prothrobinase (consists of FXa and Fva as a cofactor) activates prothrombin to form thrombin
thrombin converts fibrinogen to fibrin
What does thrombin do?
converts fibrinogen to fibrin
What inorganic compounds do we need for clotting?
Ca2+ from diet
Vitamin K from leafy greens for production of clotting factors in liver including prothrombin
how do we control clotting?
Anticoagulants:
antithrombin - inhibits thrombin and factor X and VIIII
Heparin - released by basophils and mast cells - speeds up the action of antithrombin
How do we break down clots?
Fibrinolysis:
-main enzyme is plasmin
breaks it down into fragments into fibrin degradation products - these levels can be monitored to determine if a person is producing too many clots
How do we determine if someone is producing too many clots?
the level of fibrin degradation products in their blood
