Circulation pathology Flashcards
what is the origin of platelets
platelets from a cell called megakaryocyte platelets bud off as cytoplasmic extensions and end up in blood
role of platelets in relation to trauma or tissue damage
platelets try to close the gap that tissue factors made during trauma or damage. platelets have molecules on their surfaces that allow adherence to interstitial collagen which is how they close the gap
main site of production of key clotting factors
liver or endothelial cells
mechanism of action of key clotting functions
amplification system (clotting cascade) that results in thrombin production- damage leads to release of tissue factor which produces thrombin from prothrombin which leads to production of fibrin from fibrinogen
production of fibrin in producing clots and thrombi
thrombin converts soluble fibrinogen into insoluble fibrin which forms a mesh of strands
difference between clot formation and thrombus formation
thrombus occurs in flowing blood, it is pale cream coloured, uses fibrin and platelets.
clots form in stagnant blood, fibrin and red blood cells, red in colour
what happens in thrombolysis
removal of fibrin in thrombus by plasminogen converting to plasmin and then cutting up fibrin into smaller fragments
what happens in a wound due to trauma
vasoconstriction reduces bleeding, clot formation occurs in space around vessel and may fill void, thrombus forms in flowing blood and stops bleeding from gaps on vessels
causes of thrombosis
changes in intimal surface of vessel, changes in pattern of blood flow, changes in blood constituents (virchows triad)
haemostasis
stopping of bleeding
example of changes in intimal surface of vessel
atheroma lipid coming onto surface. lipid and collagen can rupture intimal surface. platelets and fibrin now exposed to abnormal substance and turbulent flow and are deposited as thrombus
example of changes in pattern of blood flow
smoking can predispose to atheroma in coronary arteries (narrow down the lumen) so decreased blood flow so build up of fibrin and platelets
example of changes in blood constituents
smoking increases stickiness of platelets so makes more likely to clot
ischaemia
poor blood flow. if severe then this leads to hypoxia
hypoxia
low oxygenation of tissue
necrosis
tissue death
infarction
necrosis as a result of ischaemia
embolism
mass of material moving in the vascular system and able to become lodged in the vessel and block it
pulmonary embolism
sluggish flow in leg veins leads to thrombosis and clot formation, part of this breaks off and embolises, this embolus passes into inferior vena cava then to right heart then pulmonary trunk and lodges in pulmonary artery branch which leads to pulmonary infarct (lung)
thromboembolism
blockage that is broken off from a thrombus or clot and blocks further down in circulation
what is circulatory shock
profound circulatory failure causing poor perfusion of vital organs. low blood pressure and its physiological consequences. happens if low blood pressure combined with fast pulse
3 major types of circulatory shock
hypovolaemic, septic (generalised vasodilation), cardiogenic
a physiological mechanism that tries to maintain blood pressure in shock
cartotid sinuses sense if blood pressure drops and then respond by sending nerve cells to the brain stem. the brain stem in turn tells the heart to pump harder and faster
2 organs that can be damaged by shock
brain- reversible then permanent, ischaemic infarction, kidneys- reversible then severe
example of hypovolaemic shock
ruptured spleen- blood flows out of spleen so less blood in vessels so they collapse so inferior vena cava collapses so venous pressure flows to virtually zero. low volume of blood
signs of circulatory shock
low blood pressure, high pulse rate
