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what is hypoxia?

when the oxygen saturation of the tissue falls


what is ischaemia?

the disturbance or interruption of blood flow to the tissues or cells


what is the difference between ischaemia and hypoxia?

ischaemia always results in hypoxia but hypoxia can occur without ischaemia
hypoxia is lack of oxygen only
ischaemia is oxygen and metabolites - glycolytic anaerobic respiration fails, build up of metabolites impairs anaerobic respiration further
ischaemic injury is faster and more severe


what are the causes of ischaemia?

vascular occlusion - embolus, thrombus or severe atherosclerosis - arterial or venous


what are rarer causes of ischaemia?

cardiac failure, twisting of vessel roots, rupture of vascular supply, vasculitis, vasospasm and extrinsic compression


when is cell injury reversible?

when damage is limited or of short duration through the therapeutic rapid restoration of blood flow


when does cell death occur?

when there is prolonged ischaemia meaning there is irreversible cell damage


what is an example of rapid restoration where the cells can be salvaged?

primary percutaneous coronary intervention for myocardial ischaemia / infarction


why does cell death occur?

there is prolonged or sustained injury resulting in irreversible cell damage


what type of cell death is ischaemic injury?



what is tissue necrosis called when it is caused by ischaemia?



what is ischaemia?

localised tissue hypoxia that is due to decreased blood flow to an organ or tissue


what is infarction?

tissue necrosis as a result of ischaemia


vascular occlusion effects are variable and depend on four factors. what are these?

the nature of blood supply
the rate of occlusion
the tissue vulnerability to hypoxia
the blood oxygen content


what is the most important factor in determining whether vascular occlusion causes damage and why?

the nature of the blood supply and alternative supplies - if there are alternative supplies then severe ischaemia will be needed for infarction - tissues with a dual blood supply are generally resistant to infarction of a single vessel


what are examples of organs with a dual blood supply?

hands - ulnar and radial
lungs - pulmonary and bronchial
liver - hepatic artery and portal vein


what organs are susceptible to arterial infarction?

spleen the kidneys and the testis - the have an end arterial circulation and therefore artery only blood supply


what organs are susceptible to venous infarction?

the ovaries and testis, as they have only a single venous outflow


why is a slower rate of occlusion less likely to cause infarction?

there is time for an alternative blood supply to develop - collateral supply


why is the heart adapted to slower occlusion?

small anastamoses connect the major branches in the coronary artery system and they usually have minimal flow. With slow occlusions there is time to direct flow through these branches so infarction can be avoided.


how long until there is irreversible cell damage in a neurone?

3-4 minutes


which is more resistant to hypoxia, the brain or the heart?

brain - 3/4 minutes
heart - cardiac myocytes can survive for around 20-30 minutes
cardiac fibroblasts for hours as they are not as metabolically active as muscle cells
therefore the heart is more resistant


what does lower oxygen saturations of the blood result in?

more vulnerable to infarction and congestive heart failure


what is the result in congestive heart failure?

poor pulmonary ventilation and cardiac output
infarct in normally inconsequential narrowing of the vessels due to impaired oxygenation of the tissues


what will a morpholgy describe?

location, colour, shape, type of necrosis and histological changes


what are watershed regions and give three examples?

they are the point of anastamoses between two vascular supplies - the myocardium, the brain and the splenic flexure of the colon


what are the two types of infarction?

red (haemorrhage) and white (anaemic)


what is a red infarction?

where there is a dual blood supply or venous infarction


what is a white infarction?

it is a single blood supply and therefore totally cut off


what happens if the obstruction is at an upstream point of the vessel?

the tissue deeper will infarct as the branches go deeper downstream