Cell and tissue injury Flashcards
What are labile cells
Continuously divide and regenerate - epithelia/heamatopietic cells
What are stable cells
Low level of replication and can regenerate when signalled - hepatocytes/endothelial
What are permanent cells
Unable to divide - neornes/cardiac muscle fibres
Causes of cell injury
hypoxia (deficiency of oxygen)
chemical agents and poisons
infectious agents
immune-mediated processes
genetic abnormalities
nutritional imbalances
physical agents e.g. Heat
Most reversible injuries occur in…
Cytosplasm
Most irreversible injuries occur in…
Nucleus
Targets of cellular injury
Mitochondria
Plasma membrane
Lysosomes
Cytoskeleton
DNA/Nucleus
Mechanisms of cell injury
Depletion of ATP
Increased intracellular
calcium
Increase free radicals
Disruption of
membranes
DNA and protein damage
Cellular changes in reversible and irreversible injury
What is necrosis
Cell death due to lethal injury
How does necrosis occur
- depletion of intracellular energy systems, influx of Ca+
- disruption of cytoplasmic organelles
- liberation of intracellular enzymes
- production of oxygen free radicals
- disintegration of the nucleus
- alterations and failure of the plasma membranealteration in ionic transportdisruption and increased permeability
Nuclear changes in necrosis
Pyknosis: condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis.
Karyorrhexis: fragmentation of the nucleus and the breakup of the chromatin into unstructured granules.
Karyolysis:complete dissolution of the chromatin of a dying cell due to the enzymatic degradation by endonucleases.
Types of necrosis
- coagulative necrosis
- liquefactive necrosis
- fat necrosis
- fibrinoid necrosis
- caseous necrosis (caseation)
- gangrenous necrosis
Coagulative necrosis
- most common form of necrosis
- dead tissue is initially swollen and firm, but later becomes soft
Liquefactive necrosis
- characteristically occurs in cns (e.g hypoxic stroke)
- necrotic neural tissue undergoes total liquefaction and glial reaction occurs around the periphery, with eventual cyst formation
Fat necrosis
adipose tissue destruction due to:
- direct trauma - release of triglycerides following trauma elicits a rapid imflammatory response
- ezymatic lipolysis - in acute pancreatitis, lipases from damaged acini act on fat cells
Fibrinoid necrosis
- occurs in blood vessel, eosinophilia and fibrous deposits are seen e.g malignant hypertension
Caseous necrosis
Seen in tuberculosis
Complete loss of normal tissue architecture is replaced by granular and eosinophilic tissue - appearance reminiscent of cottage cheese hence term ‘caseation’
Gangrenous necrosis
- describes dead tissue
- common sites include lower limb and GI tract.
What is apoptosis
It is programmed cell death
- requires energy
Steps of apoptosis
- Initiation
- Execution
- Disposal
Mechanisms of apoptosis
- Intrinsic (mitochondrial) pathway
- Extrinsic pathway (cell membrane receptors)
Difference between necrosis and apoptosis
What is autophagy
A cellular housekeeping - takes damaged proteins, organelles and digest them into essential constituents
- occurs with membrane bound vesicles containing lysosomal enzymes
- proteins become amino acids, nucleic acids to nucleotides
Cellular response to injury
