Thrombosis PDF

Hypermia and Congestion Definition: Both of them can be defined as a local increase in volume of blood in a particular tissue. Hypermia - active process resulting from an increased inflow of blood into a tissue because of arteriolar vasodilation. - example exercising skeletal muscle or acute inflam...

Hypermia and Congestion Definition: Both of them can be defined as a local increase in volume of blood in a particular tissue. Hypermia - active process resulting from an increased inflow of blood into a tissue because of arteriolar vasodilation. - example exercising skeletal muscle or acute inflammation Congestion - is a passive process resulting from impaired outflow of blood from a tissue. - occurs systemically as in cardiac failure or locally as in isolated venous obstruction. Haemorrhage Definition: Hemorrhage is extravasation of blood outside the blood vessel. Causes: Physical trauma – Stabbing - Stick injury - Gunshot - Motor vehicle accident Inadequacies in blood clotting which can be due to: A. Too few or poorly functioning platelets B. B. Missing or low amount of clotting factors E.g. Low levels of prothrombin, fibrinogen & other precursors. Inadequate vitamin K leads to clotting factor deficiency because this vitamin is important in the synthesis of the clotting factors by the liver. Terminology: 1) Haemorrhage enclosed within a tissue or a cavity is knownas hematoma. 2) Minute 1-2 mm hemorrhages occurring in the skin, mucosal membrane, or serosal surface are called petechiae. 3) Slightly > 3mm hemorrhage occurring in the skin is referred to as purpura. 4) Larger than 1-2cm subcutaneous hematoma is called eccymosis (bruises). It is typical after trauma Effects of haemorrhage: depend on the rate and amount of blood loss: If > 20% the total blood volume is rapidly lost from the body, it may lead to hypovolumic shock & death. Chronic loss of blood leads to anaemia Thrombosis Thrombosis is defined as the formation of a solid or semisolid mass from the constituents of the blood within the vascular system. Pathogenesis of Thrombosis: Three predisposing factors for thrombus formation (Virchow's triad):. Endothelium injury: This is a dominant predisposing factor, since endothelial loss by alone can lead to thrombosis. It is particularly important for thrombus formation occurring in: Abnormal blood flow: The heart or in the arterial circulation, where the normally high flow rates might otherwise interfere with clotting by preventing platelet adhesion & diluting coagulation factors..Hypercoagulability: Hypercoagulability generally contributes less frequently to thrombosis. It is defined as: Any alteration of the coagulation pathways that predisposes to thrombosis. It is be divided into: Primary (Genetic). Secondary (Acquired). 8 Fates of a thrombus A thrombus can have one of the following fates: A: Propagation: The thrombus may accumulate more platelets and fibrin & propagate to cause vessel obstruction. B: Embolization: The thrombus may dislodge and travel to other sites in the vasculature. Such a traveling thrombus is called an embolus. An embolus may obstruct a vessel. The obstruction leads to the death of the tissue supplied by the blood vessel. Death of a tissue due to a decreased blood supply or drainage is called infarction. Therefore, an embolus can eventually lead to an infarction of an organ. E.g cerebral infarction can be caused by a thromboembolus. C: Dissolution: The thrombus may be removed by fibrinolytic activity. D:Organization and recanalization.  Venous Thrombosis Venous thrombosis affects veins of the lower extremity in 90% of cases. 1. Superficial venous thrombosis - Usually occurs in saphenous venous system, particularly when there are varicosities. - Rarely embolizes - 2. Deep venous thrombosis (DVT) - May embolize, hence, is more serious. - Usually starts in deep veins within the calf muscles. - Has higher incidence in middle aged & elderly people due to increased platelet aggregation & reduced PGI2 production by the endothelium. Has the following predisposing factors: 1. Trauma, surgery, burns which usually result in:- a:Reduced physical activity leading to stasis b:Injury to vessels c:Release of procagulant substance from the tissue d:Reduced (fibrinolysis) 2. Pregnancy & puerperal states increase coagulation factors & reduce the synthesis of antithrombotic substances. 3. Malnutrition, debilitating conditions and wasting diseases such as cancer. DVT due to these conditions is known as marantic thrombosis. 4. Inflammation of veins (thrombophlebitis) also predisposes to thrombosis. 5. Migratory thrombophlebitis is a condition that affects various veins throughout the body & is usually of obscure aetiology, but sometimes it is associated with cancer, particularly pancreatic cancer.  Arterial Thrombosis - turbulence and may ulcerate & cause endothelial injury, both of which can lead to thrombosis. These thrombi may narrow or occlude the lumen of arteries such as the coronary and cerebral arteries. Occlusion of these arteries will lead to myocardial infarction (MI) & cerebral infarction respectively. – Cardiac thrombi can be caused by infective endocarditis, atrial fibrillation, myocardial infarcion. -Apart from obstructive features, arterial thrombi (especially, cardiac mural thromi).  Embolism An embolus is a detached intravascular solid, liquid or gaseous mass that is carried by blood to sites distant from its point of origin. After traveling via the blood, the embolus can obstruct a vessel. Causes of embolism: An embolus can arise from: o Thrombus (99% of emboli arise from a thrombus. Such an embolus is called thromboembolus) o Platelets aggregates o Fragment of material from ulcerating atheromatous plaque o Fragment of a tumour o Fat globules o Bubbles of air o Amniotic fluid o Infected foreign material o Bits of bone marrow o Others. Infarction Definition: An infract is an area of ischemic necrosis caused by occlusion of either the arterial supply or venous drainage in a particular tissue. Nearly 99% of all infarcts result from thrombotic or embolic events. Other mechanisms include [almost all of them are arterial in origin]: Local vasospasm Expansion of atheroma due to hemorrage in to athermotous plaque. External compression of the vessels. e.g trauma Entrapment of vessels at hernial sacks etc. The development & the size of an infarct are determined by the following factors: A. The nature of the vascular supply B. The rate of development of occlusion C. Suceptibility of the tissue for hypoxia D. Oxygen content of the blood E. The severity & duration of ischemia