PHYSIOLOGY/PATHOLOGY - Haemostasis and Haemostatic Disorders Flashcards
What is haemostasis?
Haemostasis is a normal physiological mechanism that prevents the escape of blood from a ruptured vessel and initiates healing
Describe the process of platelet plug formation
- Injury to the endothelium triggers the release of tissue factor and expression of Von Willebrands factors
- Platelets adhere to Von Willebrands factors expressed on the endothelial cells
- Adhered platelets will release ADP and thromboxane A to attract and activate more platelets
- Platelets aggregate to form a platelet plug at the site of injury
What is thrombocytopenia?
Thrombocytopenia is a decrease in circulating platelets
What are the seven possible clinical signs of thrombcytopenia?
Epistaxis
Ecchymoses
Petechiae
Haematuria
Haematochezia
Melaena
Hyphaema
What is epistaxis?
A nosebleed
What is the difference between haematochezia and melaena?
Haematochezia is the passage of fresh blood in the faeces whereas melaena is the passage of partially digested blood in the faeces
What is hyphaema?
An accumulation of blood in the anterior chamber of the eye
How should you diagnose thrombocytopenia?
Complete blood count (CBC)
Blood smear
Manual platelet count
(T/F) Platelet function disorders present with thrombocytopenia
FALSE. Platelet function disorders are a dysfunction of platelet function rather than a decrease in the number of platelets in the blood
Which test can be done to test platelet function?
Buccal mucosal bleeding test
Name an example of a platelet function disorder
Von Willebrands disease
How should you diagnose Von Willebrands disease?
Buccal mucosal bleeding test to task platelet function followed by an ELISA - if the percentage of Von Willebrands is less than 50%, this is indicative of Von Willebrands disease
What triggers the extrinsic coagulation cascade?
Injured endothelial cells expose a tissue factor which stimulates the extrinsic coagulation cascade
Describe the common coagulation cascade
- Extrinsic or intrinsic coagulation pathway stimulates the conversion of prothrombin to thrombin
- Thrombin activates factor 13 as well as converts soluble fibrinogen into insoluble loose fibrin threads
- Activated factor 13 connects the loose fibrin threads to form and stabilise a fibrin network
- Fibrin network contracts, pulling the erythrocytes together (erythrocytes go from a biconcave to tetrahedral shape) to form a blood clot
What is fibrinolysis?
The dissolution of blood clots
Describe the process of fibrinolysis
- The presence of insoluble fibrin threads activates the enzyme t-PA
- Enzyme t-PA converts plasminogen to plasmin
- Plasmin breaks down the fibrin network of the clot, converting the insoluble fibrin threads back into soluble fibrinogen
Which diagnostic test is done to test the function of the intrinsic pathway of the coagulation cascade?
Activated partial thromboplastin time (aPTT) test
Which diagnostic test is done to test the function of the extrinsic pathway of the coagulation cascade?
Prothrombin time (PT) test
Which diagnostic test is carried out to test the function of the common pathway of the coagulation cascade?
Thrombin clotting time (TCT) test
What are the four clinical signs of coagulation disorders?
Haematomas
Gastrointestinal (GI) bleeding
Urinary tract bleeding
Haemoarthrosis
What is haemoarthrosis?
Bleeding into the joint cavity
Name an example of a hereditary coagulation disorder
X-linked haemophilia
What are the two forms of X-linked haemophilia?
Type A X-linked haemophilia
Type B X-linked haemophilia
Which clotting factor is affected by type A X-linked haemophilia?
Clotting factor VIII
Which clotting factor is affected by type B X-linked haemophilia?
Clotting factor IX
How should you diagnose X-linked haemophilia?
Activated partial thromboplastin time (aPTT) test followed by a factor deficient plasma test to identify which clotting factor is affected
List three examples of acquired coagulation disorders
Vitamin K deficiency
Severe hepatic disease
Disseminated intravascular coagulation (DIC)
List two possible causes of a vitamin K deficiency?
Biliary obstruction
Inflammatory bowel disease
How can a biliary obstruction cause a vitamin K deficiency?
A biliary obstruction limits the flow of bile which is required for the absorption of vitamin K
How can inflammatory bowel disease cause a vitamin K deficiency?
The inflammation of the intestines can limit the absorption of vitamin K
Which four clotting factors are affected by a vitamin K deficiency?
Clotting factor II
Clotting factor VII
Clotting factor IX
Clotting factor X
How should you diagnose a vitamin K deficiency?
Activated partial thromboplastin time (aPTT) test and a prothrombin time (PT) test
What is disseminated intravascular coagulation (DIC)?
Disseminated intravascular coagulation (DIC) is an aquired syndrome characterised by the activation of the coagulation cascade resulting in the formation of intravascular thrombi and the depletion of platelets and coagulation factors leading to haemorrhage
What are four possible primary causes of disseminated intravascular coagulation (DIC)?
Neoplasia
Sepsis
Endotoxaemia
Systemic inflammation
How should you diagnose DIC?
Complete blood count (CBC)
Activated partial thromboplastin time (aPPT) test
Prothrombin time (PT) test
