infarction and necrosis Flashcards
what is apoptosis?
- programmed cell death
- 50–70 billion cells undergoing apoptosis per day in an adult human
- highly-regulated process of self degradation
what does apoptosis eliminate?
- unwanted cells
- dysfunctional cells
changes to structure of cells - apoptosis
- genome fractures
- cell shrinks
- disintegrates in small apoptotic bodies
what are caspases?
- proteins that break down old or faulty cells
- can be activated via intrinsic/extrinsic pathway
apoptosis is initiated by…
factors outside the cell in the extrinsic pathway
when triggered internally…
proteins within cells are released which destroy membranes of mitochondria - this is how intrinsic pathway begins
inducers of apoptosis?
- TNF
- reduction of growth factor
- toxins
- UV + gamma radiation
- nutrient deprivation
what does excessive apoptosis lead to?
neurodegenerative disease
what does insufficient apoptosis lead to?
cancers, autoimmunity
what is necrosis?
- death of a cell caused by external factors such as injury, chemical exposure, radiation, or lack of oxygen
- it’s permanent
apoptosis vs necrosis
ischaemia
- inadequate supply of blood to an area of tissue
- cause hypooxia, malnutrition, failure to remove waste
- caused by interruption of arterial supply
consequences of ishaemia
- functional disturbances
- degeneration atrophy + replacement fibrosis
- gangrene
- infarction
infarction
area of necrosis caused by arterial/venous ischaemia
infarction causes
- thrombus
- emoblism
- hypovolaemia
- hypotension
factors which determine the degree of infarction or necrosis
- speed of onset - if sudden, then there is less time to use collateral circulation
- extent of obstruction, complete, partial occlusion
- anatomy - eg dual supply, shins (watershed)
- vulnerability to hypoxia - neurones, myocardium, fibroblasts
- oxygenation - before event
- duration
example of small area of necrosis - acute leucocytoclastic vasculitis
affected vessels w necrosis have their lumens occluded by fibrin and walls infiltered by neutrophils showing degeneration with karyorrhexis + clinically skin appears as palpable purpura
infarction development
- death of cells in an area deprived of blood supply
- dead tissue undergoes necrosis
- progressive autolysis of necrotic tisssue + haemolysis of red cells
- outward diffusion of tissue breakdown products + free haemoglobin ingested by macrophages
- infarct is now firm + dull, yellow in colour surrounded by red zone of inflammation
- followed by shrinkage of infarct which later becomes white in colour
types of infarctions
- red (haemorrhagic) infarcts - venous occlusion
- white infarcts - arterial occlusion
