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.
