Ischaemia, infarction and shock Flashcards
Define hypoxia
any state of reduced tissue oxygen availability
Define ischaemia
pathological reduction in blood flow to tissues
Are the effects of ischaemia reversible?
only if limited/for a short duration (otherwise cell death occurs)
How can the effects of ischaemia be reversed?
with therapueutic reperfusion
Does therapeutic reperfusion have an effect on infarcted tissue?
no
Define infarction
ischaemic necrosis caused by occlusion of the arterial supply or venous drainage
Define infarct
an area of infarction in tissues
What are the 2 most common causes of infarction?
thrombosis and embolism
Name some less common causes of infacrtion (5)
vasospasm, atheroma expansion, extrinsic compression, twisting of vessel roots, rupture of vascular supply
Describe red infarction
haemorrhagic - dual blood supply/venous infacrtion
Describe white infarction
anaemic - single blood supply hence totally cut off
What shape are most infarcts?
wedge
What four factors influence the degree of ischaemic damage?
nature of blood supply, rate of occlusion, tissue vulnerability to hypoxia, blood oxygen content
If there is an alternative blood supply, will the damage be more or less?
Less
Why are the kidneys, spleen and testis vulnerable to infarction?
they have single blood supplies
Are slow developing occlusions more or less likely to infarct tissues?
less likely
Why are slow developing occlusions less likely to infarct tissues?
allows time for development of alternative (collateral) perfusion pathways
What does ischaemia in the heart cause?
ischaemic heart disease (angina, MI)
What does ischaemia of the brain cause?
cerebrovascular disease (TIA/CVA)
What does ischaemia of the intestines cause?
ischaemic bowell
What does ischaemia of the extremities cause?
peripheral vascular disease/gangrene
What is meant by cerebrovascular disease?
Any abnormality in the brain caused by a pathological process involving the blood vessels
What causes ischaemic stroke?
thrombosis secondary to atherosclerosis r embolism
What causes haemorrhagic stroke?
intracerebral haemorrhage or ruptured aneurysm in circle of Willis
What is dry gangrene?
ischaemic coagulative necrosis only
What is wet gangrene?
superimposed infection
What is gas gangrene?
superimposed infection with gas producing organism
What is gangrene?
Infarction of entire portion of limb/organ
Define shock
a physiological state characterised by a significant reduction of systemic tissue perfusion resulting in decreased oxygen delivery to tissues
how does shock lead to cellular hypoxia?
impaired tissue perfusion and prolonged oxygen deprivation
What are the cellular effects of shock? (5)
- membrane ion pump dysfunction
- intracellular swelling
- leakage of intracellular contents
- inadequate regulation of intracellular pH
- anaerobic respiration
What are the systemic effects of shock? (4)
- alterations in the serum pH
- endothelial dysfunction
- stimulation of inflammatroy and anti-inflammatory cascades
- end-organ damage
What is hypovolaemic shock?
intra-vascular fluid loss
What effects does hypovolaemic shock have?
decreased venous return to heart, decreased stroke volume
How do you compensate for the effects of hypovolaemic shock?
increase systemic vascular resistance
What causes hypovolaemic shock?
haemorrhage, diarrhoea, vomitting
What is third spacing?
acute loss of fluid into internal body cavities
What is cardiogenic shock?
cardiac pump failure
What are the effects of cardiogenic shock and how do you compensate for this?
decreased cardiac output, combatted by increasing systemic vascular resistance
What are the 4 categories of cardiogenic shock?
myopthic, arrythmia-related, mechanical, extra-cardiac
What cause myopathic cardiogenic shock?
MI
What causes mechanical cardiogenic shock?
valvular defects, ventricular septal defects
What causes extra-cardiac cardiogenic shock?
anything that imparis cardiac filling or ejection of blood from heart
What is distributive shock?
decreased systemic vascular resistance sue to severe vasodilation
Which type of shock are all of the following?:
septic shock, anaphylactic shock, neurogenic shock, toxic shock syndrome
distributive shock
