Haematology II- Haemostasis and Blood Groups Flashcards
what are the 3 steps of the haemostatic response?
- vasoconstriction
- platelet adhesion and aggregation
- coagulation phase
what is the other name for platelet?
thrombocyte
why is there a continual need for production of platelets
they have no nucleus
do platelets contain granules
yes
what are the contents of granules in platelets
contain clotting factors and other elements for hemostasis e.g necessary to form platelet plug
what type of cytoplasm do platelets have
Megakaryocyte cytoplasm
what is platelet production controlled by?
no. of circulating platelets (negative feedback),
- thrombopoietin (TPO) release (increase platelet numbers)
1 megakaryocyte forms how many platelets?
4000
what is the normal lifespan of platelets?
7-10 days
what is the first stage of haemostasis when there is vessel injury and collagen exposure
platelet adhesion
platelet adhesion
adhesion- platelets stick to the area that is damaged which activates them
after platelet activation, what do platelets release?
granular contents to help platelet plug formation
which two hormones do platelets release during platelet activation
serotonin and thromboxane A2
role of serotonin and thromboxane A2 in platelet activation
enhances vasoconstriction limiting blood flow to the damaged area
what is the role of ADP in platelet activation
allows the platelet to change shape and swell allowing platelets to easily come in contact with other platelets
what is the next stage after platelet activation
platelet aggregation
during platelet aggregation what is formed
the primary haemostatic plug
primary haemostatic plug
layer of platelets that build up on top of each other across the damaged area
what does platelet activation result in which is important for blood coagulation
platelet phospholipid
what is the coagulation phase
-the endpoint
-the conversion of soluble plasma protein to the insoluble rigid polymer fibrin (fibrin clot)
are fibrin clots and platelet plugs reversible
fibrin clots are irreversible whereas platelet plugs are reversible (if you squeezed a cut it would be able to open and continue bleeding)
which pathway is the beginning of the coagulation phase
extrinsic pathway
Stage 1 of extrinsic pathway of coagulation
Tissue damage exposes collagen and releases tissue factor (initiating factor of coagulation)
stage 2 of coagulation (extrinsic pathway)
released tissue factor comes into contact with factor VII (clotting factor) to form tissue factor factor VIIa complex
stage 3 of extrinsic pathway (coagulation)
tissue factor factor VIIa complex binds with the next clotting factor (factor X) activating factor Xa
the importance of the extrinsic pathway
it is responsible for around 80-90% of the factor X that goes towards the production of the fibrin clot
what other clotting factor does the extrinsic pathway produce?
small amounts of factor IX and thrombin that feedback and activates other clotting factors including factor VIII (cofactor for factor IX) and in combination they activate factor X
1st stage of the intrinsic pathway of coagulation
factor XII which is in circulation is activated to FXIIa by other elements due to the damaged blood vessel
2nd stage of the intrinsic pathway (coagulation)
FXIIa activates FXI which activates FIX and finally activates FXa
common pathway of coagulation
both intrinsic and extrinsic pathway come together to activate factor X and create the prothrombinase complex
role of prothrombinase
activates prothrombin to thrombin
prothrombinase
consists of FXa and FVa as a cofactor
importance of thrombin
important in the feedback process e.g activates cofactors (factor VIII and factor V) and also activates more platelets
which ions are the most important for the clotting process
calcium and vitamin k
what is vitamin K necessary for?
the production of certain clotting factors in the liver including prothrombin
risk of calcium deficiency
impairs blood clotting and at risk of more bleeding
what controls blood clotting
within the plasma, there are several natural anticoagulants
what are the two anticoagulants in the plasma
antithrombin and heparin
antithrombin
inhibits thrombin
heparin
released by basophils and mast cells (co-factor that accelerates actions of antithrombin)
fibrinolysis
the breakdown of the fibrin clot
main enzyme involved in fibrinolysis
plasmin
plasmin
breaks down the fibrin into fibrin degradation products into different sizes
precursor of plasmin
plasminogen
how are blood types determined
genetically
what are blood groups
combination of surface antigens on red blood cell membrane
which blood group systems have the most clinical significance
ABO and Rh(D)
group A antibodies in plasma
anti-B
group A antigens in red blood cells
A antigen
group B antibodies in plasma
anti-A
group B antigens in red blood cell
B antigen
group AB antibodies in plasma
none
group AB antigens in RBC
A and B antigens
group O antibodies in plasma
anti-A and anti-B
group O antigens in RBC
none
role of antibodies in plasma
protect against the antigen that doesn’t exist on the RBC
what occurs when antibodies come across opposing antigens on RBCs
antibodies will stick to the RBC (agglutination) and start to break down the rbc and block the blood vessels which will inevitably cause anaemia
ABO: which are dominant, which are recessive
A and b are dominant
O gene is recessive
what does the Rh blood group determine
whether a person’s blood is positive or negative (Rh + or Rh -)
-this is the presence or absence of the D antigen
why will an Rh(-) individual not usually have anti Rh (D) antibodies
this requires sensitisation by exposure to the Rh (+) RBCs
when might exposure to the Rh(+) RBCs occur
transfusion
pregnancy/ birth
what percentage of the population are Rh positive and what are Rh negative
85% are Rh positive
15% are Rh negative
is there a link between abo and rh
no
how would haemolytic disease of a newborn occur?
if the mother had Rh- blood and the fetus has Rh+ blood
describe the haemolytic disease of the new-born
during childbirth, haemorrhage of the placenta causes exposure of the mother’s blood and the foetus’s blood
-if the foetus were to have rh+ blood and the mother was to have rh- blood, mother’s immune system would start to produce antibodies to fight against the ‘foreign’ blood cells
-if this were to occur, these antibodies would cross the fetal tissue. bind to the baby’s rbc and destroy them putting the baby at risk of developmental issues, anaemia or it could be fatal
what would happen if the mother were to get pregnant again
the mother would already have the antibodies against the fetal RBCs and this would cause hemolysis
how is haemolytic disease of a new born prevented
the mother may be given anti-d to prevent an immune response to the babies blood cells
which blood group is known as the universal donor
O- as the blood cells have no surface antigens therefore an immune response will not occur with any other blood group
which blood group is known as the universal acceptor
Blood group AB as they conatin both A and B surface antigens on their RBCs therefore no antibodies against A or B
