Intro to haemostasis Flashcards
haemostasis
arrest of bleeding and maintenance of vascular patency
requirements of haemostasis
permanent state of readiness- ASAP
prompt response
localised response ; only where there is injury
protection against unwanted thrombosis
what are the components of the normal haemostatic system
formation of platelet plug
formation of fibrin clot
fibrinolysis
anticoag defences
primary haemostasis
initial rapid response to vascular bleeding
platelet adhesion and aggregation to form form a temporary platelet plug
secondary haemostasis
formation of fibrin clot
involves coagulation cascade
how are platelets formed
in bone marrow by budding from megakaryocytes
fibrinolysis
break down of blood clots
occurd after clot is formed to allow blood to go round the body
largest cells to spot
megakaryocytes
structure of platelets
small enucleate discs with a mean life span of 7-10 days
platelet aggregation steps
When theres an injury, vessel wall damage exposes collagen, platelets have receptors for collagen so stick to it
VWF is released and platelets stick with that too- localized response
Platelet adhesion^
Block the injury so send out chemical with adp being released- sends messages to other platelets- platelet aggregation – primary haemostasis
causes of failure of platelet plug formation
thrombocytopenia
platelet function disorders
disfunction of VWF
antiplatelet drugs
what might impair platelet adhesion to vessel wall
deficiency of VWF
consequences of failure of platelet plug formation
purpura , spontaneous bruising
mucosal bleeding
intracranial haemorrhage
retinal haemorrhages
menorhaggia
screening tests for primary haemostasis
platelet count
failure of fibrin clot formation causes
Single clotting factor deficiency
usually hereditary
eg Haemophilia
Multiple clotting factor deficiencies
usually acquired
eg Disseminated Intravascular Coagulation
Increased fibrinolysis
usually part of complex coagulopathy
vvit k def
dysfunctional fibrinogen
liver disease
where are clotting fcators made
in the liver
hwo is plasmin formed
from precursor plasminogen by tissue plasminogen activator
consequences of failure of fibrin clot formation
Pattern of bleeding depends on
Single/multiple abnormalities
The clotting factors involved
no charcaterisitc clinical syndrome
screening tests for fibrin clot formation
prothrombin time
activated partial thromboplastin time
thrombin time
what does thrombin time measure
fibrinogen conversion to fibrin by thrombin
naturally occuring anticoags
serine protease inhibitors
protein c and protein s
what are serine proteases
enzymes involved in blood coagulation
thrombophilia
blood clots more than normal
