Physiology: Application - Haemostasis Flashcards
what is haemostasis
arrest of bleeding and maintenance of vascular patency
components of normal haemostatic system (what can happen)
- formation of platelet plug
- formation of fibrin clot
- fibrinolysis
- anti-coagulant defences
how and where are platelets formed
formed in bone marrow by budding from megakarocytes
describe how a platelet plug is formed
endothelial damage exposes collagen and releases VWF and other proteins, platelets have receptors to these and attach at the site of injury
platelets secrete chemicals leading to platelet aggregation at sit of injury
causes of failure of platelet plug formation (4)
- vascular
- low platelet count (thrombocytoenia)
- decreased platlet function
- VWF
what are the consequences of failure of platelet plug formation (4)
- spontaneous bruising and purpura
- mucosal bleeding
- intracranial haemorrhage
- retinal haemorrhage
what is primary haemostasis
platelet plug formation
what is secondary haemostasis
fibrin clot formation
describe the process of fribrin clot formation
- TF and VIIa initiate clotting
- V and Xa propagate prothrombin to thrombin
- this changes fibrinogen to fibrin which causes the clot
- thrombin amplifies the pathway via VIII and IXa
what are the causes fibrin clot failure (3)
- single clotting factor deficiency (hereditary)
- multiple clotting factor deficiencies (acquired)
- increased fibrinolysis
what is fibrinolysis
breakdown of fibrin in blood clot
describe fibrinolysis
- tpa activates plasmin from plasminogen
- plasmin changes fibrin to fibrin degredation products
what are the consequences of failure of fibrin clot formation
- no characteristic syndrome
- causes bleeding
- primary or secondary haemostatic failure
what does the bleeding pattern in fibrin clot failure depend on
- if its single or multiple abnormalities
- clotting factors involved
name 2 naturally occuring anto-coagulants
- serine protease inhibitors
- proteins C and S
how do serine protease inhibitors work (anti-thrombin III)
- anti-thrombin III inhibits clotting factors TF/VIIa, V/Xa, VIII/IXa and thrombin
- this stops fibrin clot formation
how to proteins C and S work
- activated by thrombin and bind to thrombomodulin
- inhibit clotting factors V/Xa and VIII/IXa
what is thrombomodulin
thrombin co-factor that decreases coagulation by converting thrombin to and anti-coagulation enzyme
describe arterial thrombus and its treatment
- atherosclerosis
- platelet rich
- aspirin and anticoagulants, modify atherosclerotic risk factors
describe venous thrombus and its treatment
- plateltes not activated- coagulation cascade activated, fibrin rich clot
- heparin, warfarin or new O anticoagulants
what is virchows triad
- factors that contribute to coagulation
- blood stasis, hypercoagulation and endothelial injury
what happens with unstable atherosclerotic plaques when they rupture
- platlets are activated causing an actute thrombus
- sudden symptom onset
where might and atherosclerotic rupture happen, what are the assoc. disease and what are the consequences of that
- coronary arteries, unstable angina/MI
- cerebral arteries, stroke
- leads to acute organ ischaemia and necrosis
describe the symptoms of DVT
- limbs feel swollen, hot or tender
- pitting oedema
what can happen as a consequence of PE
- pulmonary infarct, pleuritic chest pain, CV collapse/death
- hypoxia
- R heart strain
