Ischaemia and Infarction Flashcards
What is the definition of Infarction?
Infarction: Ischaemic necrosis within a tissue/organ in living body produced by occlusion of either the arterial supply or venous drainage
What is the definition of Ischaemia?
Ischaemia: Relative lack of blood supply to tissue/organ leading to inadequate O2 supply to meet needs of tissue/organ
What are the four types of hypoxia?
Hypoxic - high altitudes, low partial pressure of O2
Anaemic - low haemoglobin
Stagnant - abnormal delivery of O2, local (occlusion), systematic (shock, hypotension)
Cytotoxic - respiring organelles don’t work properly
What are the factors affecting O2 supply?
- Inspired O2
- Pulmonary function- oedema ?
- Blood constituents – enough haemoglobin
- Blood flow – turbulence, stasis
- Integrity of vasculature – tumour, atheroma
- Tissue mechanisms – cells have to work properly, organelles
- Previous MI
What factors could effect the O2 demand?
- exertion eg. exercise, stress
2. heart has a high intrinsic demand of oxygen
Is there a clinical correlation between atheroma and ischaemia?
established atheroma = stable angina complicated atheroma (fissuring, rupture) = unstable angina
complicated atheroma -> thrombosis -> ischaemia/infarction
name six clinical consequences of ischaemia.
¥ MI ¥ TIA – symptoms of a stroke lasting for less than 24 hours ¥ Cerebral infarction ¥ Abdominal aortic aneurysm ¥ Peripheral vascular disease ¥ Cardiac failure
What are the functionally effects of ischaemia?
Blood/O2 supply fails to meet demand due to decreased supply; increased demand
What are the general effects of ischaemia?
¥ Acute – obvious signs, breathlessness, chest pain
¥ Chronic – insidious signs
What are the biochemical effects of ischaemia?
decrease of O2 more anaerobic respiration acid base balance is altered pH decreases this causes cell death
What are the cellular effects of ischaemia?
¥ Cells with high metabolic rate – greatly and quickly effected (require more O2)
¥ Cells with low metabolic rate - less effected
What causes infarction??
cessation of blood flow
Name four ways which can stop blood flow.
- Thrombosis
- Embolism
- Strangulation e.g. gut twisted
- Trauma - cut/ruptured vessel
What does the scale of damage form infarction depend on?
- Time period
- Tissue/organ (site in the body)
- Pattern of blood supply – number of arteries supplying the area
- Previous disease
- Size of infarction
State the sequence of events that cause infarction.
coronary artery obstruction (atheroma, thrombosis) decreased blood flow ischaemia anaerobic respiration (pH decreases) increased cell death liberation of enzymes breakdown of tissue