Cell Injury Flashcards
What does the degree of cell injury depend on?
Type of injury
Severity o injury
Type of tissue
As a physiological stimulus becomes more harmful, what is the cell response?
Homeostasis > cellular adaptation > cellular injury > cell death
What can cause cell injury?
- Hypoxia
- Toxins
• Physical agents – Direct trauma – Extremes of temperature – Changes in pressure – Electric currents
- Radiation
- Micro-organisms
- Immune mechanisms
- Dietary insufficiency and deficiencies, dietary excess
What is hypoxia?
deficiency in the amount of oxygen reaching the tissues
Name and explain 4 causes of hypoxia
– Hypoxaemic hypoxia – arterial content of oxygen is low
• Reduced inspired p02 at altitude
• Reduced absorption secondary to lung disease
– Anaemic hypoxia – decreased ability of haemoglobin to carry oxygen
• Anaemia
• Carbon monoxide poisoning
– Ischaemic hypoxia - interruption to blood supply
• Blockage of a vessel
• Heart failure
– Histiocytic hypoxia – inability to utilise oxygen in cells due to disabled oxidative phosphorylation enzymes
• Cyanide poisoning
How long do a) neurones and b) fibroblasts survive w/ hypoxia?
Extent of injury depends on which tissues injured
Neurones = few mins Fibroblasts = few hours
How does the immune system damage the body’s cells?
- Hypersensitivity reactions - host tissue is injured secondary to an overly vigorous immune reaction, e.g., urticaria (= hives)
- Autoimmune reactions - immune system fails to distinguish self from non-self, e.g., Grave’s disease of thyroid.
Which cell components are most susceptible to injury?
- Cell membranes - plasma and organnellar
- Nucleus - DNA
- Proteins - structural (enzymes)
- Mitochondria
What happens at the molecular level in hypoxia?
Less oxygen
Less oxyphos
Less ATP
- Decreased activity of Na pump so influx of Ca2+, H2O and Na+, efflux of K+. This causes swelling, loss of microvilli, Blebs, ER swelling, myelin figures
- Increased glycolysis leads to decreased pH and glycogen, leads to clumping of nuclear chromatin
- detachment of ribosomes leads to decreased protein synthesis, leading to lipid deposition
What happens in prolonged hypoxia?
Increase in intracellulr calcium leads to activation of
- ATPase - decreased ATP
- Phospholipase - decreased phospholipids
- Protease - disruption o membrane and cytoskeletal proteins
- Endonuclease - nuclear chromatin damage
Describe cell injury with causes other than hypoxia
- Sequence of events for other insults may be different but as the cell has a limited responses to injury, outcome often similar.
- Other forms of injury might attack different key structures, e.g., extreme cold (e.g., frostbite) damages membranes initially.
- Free radicals also damage membranes primarily.
What are free radicals?
- = reactive oxygen species
- Single unpaired electron in an outer orbit – an unstable configuration hence react with other molecules, often producing further free radicals
Name 3 free radicals with a particular biological significance in cells
- OH• (hydroxyl) - the most dangerous
- O2- (superoxide)
- H2O2 (hydrogen peroxide)
When are free radicals produced?
- Normal metabolic reactions: e.g., oxidative
phosphorylation - Inflammation: oxidative burst of neutrophils
- Radiation: H2O -> OH•
- Contact with unbound metals within the body: iron (by Fenton reaction) and copper
• Free radical damage occurs in haemachromatosis and Wilson’s disease - Drugs and chemicals: e.g., in the liver during metabolism of paracetamol or carbon tetrachloride by P450 system
How does the body control free radicals?
- Anti-oxidant scavengers: donate electrons to
the free radical – vitamins A, C and E - Metal carrier and storage proteins (transferrin, ceruloplasmin): sequester iron and copper
- Enzymes that neutralise free radicals
– Superoxide dismutase
– Catalase
– Glutathione peroxidase
How do free radicals injure cells?
• If the number of free radicals overwhelms the anti-
oxidant system = oxidative imbalance
• Most important target are lipids in cell membranes.
– Cause lipid peroxidation.
– This leads to generation of further free radicals → autocatalytic chain reaction.
• Also oxidise proteins, carbohydrates and DNA
– These molecules become bent out of shape,
broken or cross-linked
– Mutagenic and therefore carcinogenic
How else can cell protect itself against injury?
- Heat shock proteins
- In cell injury heat shock response aims to ‘mend’ mis-folded proteins and maintain cell viability.
- Unfoldases or chaperonins.
- An example – ubiquitin.
What do injured/dying cells look like under a light microscope?
In hypoxia:
•Cytoplasmic changes
•Nuclear changes
•Abnormal cellular accumulations
What are some irreversible changes to injured cells?
Pyknosis - nucleus shrinks
Karyorrhexis - nucleus breaks up
Karyolysis - nucleus dissolves
What do injured and dying cells look like under an electron microscope?
Reversible - blebs, generalised swelling, clumping of chromatin, autophagy by lysosomes, ER swelling, dispersion of ribosomes, mitochondrial swelling, small densities, aggregation of intramembranous particles
Irreversible - rupture of lysosomes and autolysis, nucleus pykinosis/karyolysis/karyorrhexis, defects in cell membrane, muslin figures, lysis of ER, mitochondrial swelling, large densities
How is cell death diagnosed?
Best way to tell when cell is irreversibly damaged - not by look, by function
Dye cells - when membranes leaky, dye taken up into cells
Define oncosis and necrosis
• Oncosis: cell death with swelling, the spectrum of
changes that occur in injured cells prior to death
• Necrosis: in a living organism the morphologic
changes that occur after a cell has been dead some
time
– Seen after 12-24 hours
What are the 2 main types of necrosis?
• Two main types:
– Coagulative
– Liquefactive (colliquitive)
• Two other special types:
– Caseous
– Fat necrosis
Why are there 2 types of necrosis?
2 causes
1) protein desaturation -> coagulate necrosis e.g. ischaemia of solid organs
2) enzyme release -> liquefaction necrosis e.g. ischaemia in loose tissues; presence of many neutrophils
What does coagulation necrosis look like?
•Denaturation of proteins dominates over release of active proteases.
•Cellular architecture is somewhat preserved, “ghost outline” of cells.
(SEE SLIDE)
What does liquefactive necrosis look like?
•Enzyme degradation is substantially greater than denaturation.
•Leads to enzymatic digestion (liquefaction) of tissues.
(SEE SLIDE)