Session 5 Flashcards
What is haemostasis?
The body’s response to stop bleeding and subsequent loss of blood.
What does successful haemostasis depend on?
Vessel wall - constricts to limit blood loss
Platlets - adhere to damaged vessel wall to form a platlet plug
Coagulation system
Fibrinolytic system
Outline the regulation of the coagulation system
Thrombin actively feeds back on factors V, VIII and XI.
Thrombin inhibitors include anti-thrombin III, alpha 1 anti trypsin and protein C or S.
What enzyme carries out fibrinolysis and how is stimulated?
Plasmin
Streptokinase and tPA activate the conversion of plasminogen to plasmin
What is a thrombus?
The formation of a solid mass of blood within the circulatory system during life
What changes can result in the formation of a thrombus?
Virchow’s triad:
Changes in blood flow - stagnation/turbulence
Changes in vessel wall - atheroma/injury/inflammation
Changes in blood components - smokers/pregnancy
Describe the appearance of arterial and venous thrombi
Arterial - pale, granular, lines of Zahn, lower cell content
Venous - deep red, soft, gelatinous, higher cell content
What are the effects of arterial and venous thrombi?
Arterial - ischaemia, infarction. Depends on site and collateral circulation
Venous - congestion, oedema, ischaemia (if tissue pressure due to oedema>arterial pressure)
What are the outcomes of thrombosis?
Lysis - complete dissolution of the thrombus, fibrinolytic system active and blood flow reestablished. Most likely when thrombi are small.
Propagation - the progressive spread of thrombosis; distally in the arteries and proximally in the veins
Organisation - a reparative process with ingrowth of fibroblasts and capillaries. The lumen remains obstructed.
Recanalisation - blood flow incompletely established by one or more channels forming through organised thrombus.
Embolism - part of the thrombus breaks off and becomes lodged at a distant site
What is an embolism?
The blockage of a blood vessel by a solid, liquid or gas at a site distant from its origin.
>90% are thrombo-emboli. Other types are air, amniotic fluid, nitrogen, tumour cells.
Describe the various destinations of different thrombo-emboli
From systemic veins -> lungs
From the heart -> renal, mess thrice and other arteries
Atheromatous carotid arteries -> brain (stroke)
Atheromatous abdominal aorta -> arteries of the legs
What are the predisposing factors and treatment for deep vein thrombosis?
Immobility, post operative, pregnancy/post partum, oral contraceptives, severe burns and cardiac failure.
Treatment - IV heparin (anticoagulant, cofactors for anti thrombin III) and/or oral warfarin (slow effect, interferes with synthesis of vitamin K dependent clotting factors).
What are other types of embolism other than thrombo-emboli?
Fat embolism - fractures of long bones or laceration of adipose tissue
Cerebral
Iatrogenic - eg air embolism from injection
Nitrogen - N2 bubbles form in the blood with rapid decompression, “the bends”.
What are the signs of massive, major, minor and recurrent pulmonary embolisms?
Massive - >60% reduction in blood flow is rapidly fatal
Major - medium sized arteries blocked. Shortness of breath, cough and blood stained sputum
Minor - small peripheral arteries blocked. Minor shortness of breath
Recurrent -> pulmonary hypertension
What is disseminated intravascular coagulation?
A pathological activation of Coagulative mechanisms in response to a variety of diseases. Small clots form throughout the body, disrupting normal coagulation because they use up all the clotting factors. Abnormal bleeding occurs from the skin.
What is haemophilia?
X linked recessive deficiency in different clotting factors (type A - factor VIII. Type B - factor IX) due to a nonsense mutation.
There is haemorrhage into major joints and retro peritoneum. Muscle bleeding causes pressure and necrosis of nerves. Treated with self administered factor replacement therapy.
What is thrombocytopenia?
Low platelet count due to failure of production, increase in destruction or sequestering of platlets. Usually accompanied by bone marrow dysfunction (e.g.leukaemia/anaemia). If due to sequestering, cause may be disseminated intravascular coagulation.
