Haemorrhage, haemostasis and thrombosis Flashcards
What is a haemorrhage?
- bleeding
- red blood cells escaping from a blood vessel
What can cause a haemorrhage?
- abnormal function
- loss of integrity of:
- vessels or endothelium
- platelets
- coagulation factors
How can changes in vessels and endothelium cause a haemorrhage?
- Congenital/ acquired abnormalities in vessels
- e.g. ruptures aneurysm
- abnormal collagen in Ehlers-Danlos syndrome (abnormal wall strength)
- Vit C deficiency
- Trauma
- Vascular erosion
- e.g. fungi eroding vessel walls
- Endothelial injury
- endotocin, endotheliotropic viruses, uraemic toxins
- Endothelial injury
What issues can occur with platelets causing haemorrhage?
- decreased platelet numbers (thrombocytopenia)
- decreased production (e.g. radiation)
- increased loss (e.g. immune mediated)
- increased use (e.g. DIC)
- abnormal platelet function (thromboctopathy)
- congenital defects in platelet function
- NSAIDs (asparin)
- Uremia
- vWD (lack of platelet adhesion)
How do coagulation factor deficiencies cause haemorrhage?
- Congenital deficiencies
- Acquired deficiencies
- severe liver diseases resulting in decreased synthesis of factors
- Vit K deficiency (factor II, VII, IX, protein C + S reduction)
What is this showing?
- Petechia (Peterchiae) = a pinpoint haemorrhage
- Ecchymosis (Ecchymoses) = a larger (2/3cm) haemorrhage
What can cause petechiae?
- electricution (stunning)
What is ‘Suffusive haemorrhage’?
- affects larger areas of tissue
What is this showing?
- spleen
- Haematoma = haemorrhage confined to a focal space
What is this showing?
- Haemopericardium
What would you call a haemorrhage in the thorax, pericardium and abdomen?
- Thorax - haemothorax
- Pericardium - haemopericardium
- Abdomen - haemoabdomen/ haemoperitoneum
What are the antithrombotic factors?
- tPA (fibrinolysis)
- thrombomodulin (blocks coagulation cascade)
Describe the important points of the coagulation cascade
- amplifying series of enxymatic conversions of proenzymes to active enzymes
- culminates in thrombin formation
- thrombin is the most important
What is the role of thrombin?
- acts at numerous stages in cascade
- coverts soluble fibrinogen into fibrin monomers
- fibrin monomers polymerise into insoluble fibrin gel encasing platelets and circulating cells into a haemostatic plug
Describe the process of fibrinolysis
- begins as soon as injury occurs
- limits size of haemostatic plug and then remove it after vessel is healed
- plasminogen is cleaved to form plasmin
- plasmin binds fibrin to limit growth of fibrin clot
- fibrin degradation products interfere with fibrin polymerisation, inhibit thrombin, and coat platelets to inhibit aggregation
Describe Virchow’s Triad (and what is thrombosis?)
- thrombosis - formation of an inappropriate clot on the wall of a blood or lymphatic vessel or free in lumen
What is this and why does it occur?
- arterial mural thrombosis
- the clot becomes more linear as it grows, due to the fast flowing blood in the arteries
What is this showing?
- Lines of Zahn = alternating layers of platelets and fibrin admixed with erythrocytes
- clot grows layer by layer
- will look different if dead
What is this showing and why does it occur in this way?
- Venous thrombosis - typically occlusive
- blood is going slower - the clot can grow and fill the space
What is this showing?
- thrombosis
What levels of thromosis are these 3 showing?
- A - smaller thrombi removed by thrombolysis
- B - larger thrombi removed by phagocytosis of thrombolytic debris and granulation tissue formation, fibrosis and regrowth of endothelium on surface
- C - Occlusive thrombi- invaded by new fibroblasts and then recanalised by new vascular channels
- What is this showing?
- Recanalisation
What does this show?
- thromboemboli
- saddle thrombus at the iliac bifurcation in a cat with hypertrophic cardiomyopathy
