Introduction and overview to haemostasis Flashcards
Define haemostasis
arrest of bleeding and maintenance of vascular patency
what are the requirements of haemostasis
it is ready at any time and immediate to act
acts at local site of injury
protection against unwanted thrombosis
what are components of a normal haemostatic system
primary haemostasis - platelet plug
secondary haemostasis - fibrin clot
fibrinolysis
anticoagulant defences
what kind of disorder do you have if your haematostatic system is underactive
bleeding disorder
what kind of disorder do you have if your haematostatic system is overactive
clotting disorder
what are megakaryocytes
large multinucleate cells found in the bone marrow only
how are platelets formed
budding off from megakaryocytes
what are platelets
small anucleate rings with a lifespan of 7-10days
how long should a patient stop antiplatelets prior to surgery
1 week
what is primary haemostasis
formation of platelet plug
is a platelet plug strong
no, it is weak
suitable for small injuries but not sufficient in greater damage
explain the process of primary haemostasis
Endothelial damage exposes collagen
Platelets and VWF bind to collagen
VWF helps platelets adhere to collagen and other platelets
Secretion of other chemicals help platelet aggregation
what are causes of failure of primary haemostasis
vascular: collagen deficiency
platelets: reduced number or function
VWF deficiency
what are symptoms and signs of primary haemostatic failure
spontaneous bruising senile purpura purpura on legs mucosal bleeding: nose, conjunctiva, mouth, GI tract, menorrhagia intracranial haemorrhage retinal haemorrhage - fundoscopy
what investigation can be done for primary haemostatic failure
platelet count
what is the term for high platelets
thrombocytosis
what is the term for low platelets
thrombocytopaenia
what is secondary haemostasis
formation of fibrin clot
is a fibrin clot strong
yes, fibrin strengthens the platelet plug
platelets are full of -ve phospholipids and Ca2+, true or false
true
clotting factors are negatively/positively charged
negatively charged
explain the process of secondary haemostasis
Tissue Factor activates factor 7
this complex activates factors 5+10
these then activate prothrombin to form thrombin
thrombin then converts fibrinogen to fibrin
fibrin is the final product
thrombin also acts in a positive feedback to activate factors 8+9
8+9 also activate factors 5+10
whole process is amplified
list the main categories for failure of secondary haemostatic failure
single deficiency
multiple deficiencies
features of single deficiency in secondary haemostatic failure
hereditary
rarer
eg haemophilia
which clotting factor is deficient in haemophilia A
factor 8
which clotting factor is deficient in haemophilia B
factor 9
what is a cause of multiple deficiencies in secondary haemostatic failure
disseminated intravascular coagulation DIC
list causes of DIC
sepsis cancer ABO incompatibility RTA liver disease
what is the pathophysiology behind DIC
increase in clot formation leading to widespread ischaemia
paradoxically there is also increased bleeding due to depletion of clotting factors
what is fibrinolysis and what is its purpose
break down of fibrin clots
to maintain vascular patency
occurs when fibrin clot has formed and bleeding has stopped
what is the process of fibrinolysis
tPA activates plasminogen into plasmin
plasmin breaks fibrin into FDPs
what are d dimers
fibrin degradation products
generally, failure of secondary haemostasis has characteristic symptoms, true or false
false
what are symptoms of single deficiency secondary haemostatic failure
bleeding into joints and muscles
what tests can be done to investigate fibrin clot formation as coagulation screen
prothrombin time PTT
activated partial thromboplastin time APTT
what does prothrombin time measure
length of time taken for clot formation via extrinsic pathway
prothrombin time measure extrinsic/intrinsic pathway
extrinsic
which clotting factors can be tested in prothrombin time
TF/3, 7, 5, 10, PT
clotting factors 8+9 are tested in prothrombin time, true or false
FALSE
what does activated partial thromboplastin time (APTT) measure
length of time taken for clot formation via intrinsic pathway
APTT measure extrinsic/intrinsic pathway
intrinsic
which clotting factors are tested in APTT
8, 9, 5, 10, PT
if there is a deficiency in factor 7, PT/APTT would be prolonged
PT
if there is a deficiency in factor 8, PT/APTT would be prolonged
APTT
list some naturally occurring anticoagulants
serine protease inhibitors eg anti thrombin
Protein C + S
how does anti thrombin work
inhibits thrombin and so switches off haemostasis
how do Protein C+S work
bind to factors 5+8 to switch off coagulation
what would occur as a result of antithrombin/Protein C/S deficiency
excess clotting because you cant stop anticoagulation
define thrombophilia
increased tendency to forming clots eg DVT, PE, VTE
