Cell injury and necrosis

Question 1

Causes of cell injury (broad)

Answer 1

• Hypoxia (deficiency of tissue oxygen) • Chemicals and drugs • Micro-organisms • Immunological and allergic reactions • Genetic diseases • Nutritional imbalance * Metabolic abnormalities

Question 2

Mechanisms of cell injury (more specific) (4)

Answer 2

• mitochondria damage : depletion of ATP and increased production of reactive oxygen species (ROS) - depletion of ATP - failure of ATP-dependent pumps etc - disturbance of calcium homeostasis -> entry of Ca2+ into cell - damage to cell membranes (plasma membrane and lysosomal membrane) - damage to DNA and misfolding of proteins

Question 3

How does disturbance of calcium homeostasis lead to cell injury?

Answer 3

(1) increase mitochondrial permeability - lead to ROS, and decreased ATP (2) active cell enzymes (ATP-ase, phospholipse, protease, endonuclease) End up with: - decreased ATP - membrane damage - nuclear damage

Question 4

Features of reversible cell injury

Answer 4

• cell swelling (due to failure of energy-dependant pumps) - accumulation of lipid in cells that normally metabolise it (hepatocytes, myocardial cells) - livery - shows Mallory-Denk body (cell injury seen in alcholoic poisoning)

Question 5

How does reversible cell injury -> irreversible cell injury How can you tell which way an injured cell will go?

Answer 5

• uncorrectable mitochondrial dysfunction (can’t get ATP via oxidative phosphorylation - loss of cell membrane integrity Can’t tell by looking which way a cell will no (no identified biochem or str change)

Question 6

When can you see microscopic change of cell injury

Answer 6

Biochemical changes occur before structural changes cell can be dead without any microscopic change - so it takes a while eg in ischaemia - myocytes die within 30min, but no change in H&E for 12hrs

Question 7

Necrosis - nucleus changes - cytoplasm changes

Answer 7

Nucleus - breakdown of DNA/proteins (1) pyknosis = shrinkagge + increased basophilia (cessation of DNA transcription) (2) karyorrhexis = fragmentation of nucleus (3) karyolysis = total dissolution of nucleus - ghost outline => hypereosinophilia cytoplasm - increased eosinophilia due to increased eosin binding to damaged protein + loss of ribosomes

Question 8

Apoptosis process

Answer 8

Terminally injured cells activate caspases that degrade DNA/proteins caspases = mediators of cell death Signal is sent Loss of surface specialisations/connections Cell shrinks Degradation + breakdown of cell Cell splits into apoptotic bodies Bodies are phagocytosed

Question 9

Is there a reversible stage of apoptosis? Necrosis?

Answer 9

Apoptosis - no Necrosis -there is reverssible cell injury, if irreversible then it progresses to necrosis

Question 10

What are the 2 pathways of apoptosis? Describe them

Answer 10

Intrinsic (mt) and Extrinsic (death receptor) Intrinsic - normally the Bcl-2 family of sensors receives survival signals (eg growth factors) - produce anti-apoptotic proteins (Bcl2,Bclx) - if there is no survival signal, or there is DNA damage, the sensors are activated - the Bcl2 family of effectors (Bax, Bak) then stimulate the Bax/Bak channel of mitochondria -> leakage of cytc/other pro-apoptotic proteins from mt - these stimulate initiator caspases, which stimulate executioner caspases -> common pathway Extrinsic - Receptor-ligand interaction (ligands eg - FasL on CD8, TNF) - stimulation of adapter protein - these stimulate initiator caspases -> stimulate executioner caspases Common pathway - executioner caspase effects: - endonucelase activation -> DNA fragmentation - breakdown of cytoplasm -> formation of apoptotic bodies

Question 11

What are some patterns of tissue necrosis

Answer 11

Coagulative Caseous Liquefactive Fibrinoid (fat necrosis)

Question 12

Coagulative necrosis - morphology - under what circumstances does it occur (broad) - examples

Answer 12

Morph: ghost outlines persist - tissue keeps its cell/tissue architecture for a few days Occurs where enzyme dissolution is slow Examples: infarction in solid organs (except brain = liquefactive)

Question 13

Liquefactive necrosis - morphology - examples

Answer 13

Tissue becomes viscous liquid mass/cavity due to digestion of cells Examples: cerebrain infarction; abscess -> pus

Question 14

Caseous necrosis - morphology - examples

Answer 14

Morph: macro - “cheesy” histo - amorphous granular debris (pink); with no distinct cell borders Examples: TB - necrotising granulomatous inflammation

Question 15

Fibrinoid necrosis - morphology - how does it occur - examples

Answer 15

Morphology - is only seen at microscopic level - bright pink (fibrin) Occurs due to deposition of immune complexes -> leakage of fibrin Examples - immune reactions involving blood vessels - vasculitis, serum sickness, malignant hypertension

Question 16

Fat necrosis - what is it - how does it happen - histology

Answer 16

Destruction of fat Is classicaly the result of lipases (eg in acute pancreatitis) - lipases digest cell membrane, release TAGs, these are converted to FAs - FAs combine with Ca2+ - deposits Histology - large fat droplets with n nuclei - granular pink material - later on: foamy macrophages Morphology: chalky white deposits (FA + Ca2+)

Question 17

Pigments - what do these look like, where are they found, what do they mean: - Carbon - Lipofuschin - Melanin - Haemosiderin

Answer 17

Carbon - eg in lung macrophages; means smoking etc. Lipofuschin - “wear and tear” pigment - accumulate as you age - yellow-brown on H&E, near nucleus - see in brain, heart, liver - complexes of lipid + protein, formed through oxidative injury - no pathological significance Melanin - dark - in melanocytes/keratinocytes - tumours - naevi, melanoma Haemosiderin - large brown granules on H&E - stain blue with Prussian blue - large aggregates of ferritin molecules - pathologic

Question 18

Why might you have intracellular accumulations?

Answer 18

• less removal of normal substance - accumulation of an abnormal substance - genetic defect (eg alpha1 antitrypsin deificiency, can’t export a1 antytripsin) - failure to degrade metabolite - genetic deficiency (eg glycogen storage disease) - deposition of exogeneous substance which can’t be degraded (carbon, silica)

Question 19

Pathological calcifications - what does it look like - what are the 2 types, what do they form as a result of

Answer 19

Abnormal deposition of ca salts, see on histology in ECM - rounded, deep purple bodies with layers (1) Dystrophic - occur in degenerate, necrotic tissue (atherosclerotic plaques, necrotic tumour, aortic stenosis) (2) Metastatic - as a result of high blood Ca (hyperparathyroid, chronic renal failure, hypercalcaemia of malignancy)

Question 20

What is autolysis?

Answer 20

Cell breakdown when removed from body - due to lysosome enzymes - must fix with formalin, cool in order to retain cell/tissue structure

Question 21

Necrosis v. apoptosis

• causes
• extent
• histology
• plasma membrane changes
• inflammation
• markers

Answer 21

Apoptosis

Necrosis

Causes

• normal physiological processes
• infection
• immunological disease
• drug interactions etc

Always pathological

Extent of effect

Cell by cell

Involves whole tissue area

Histology

• shrinks, breaks into apoptotic bodies with nuclear fragments (eosinophilic)
• cell breaks down due to loss of plasma membrane
• leakage of enzymes
• change in nucleus
• eosinophilia of cytoplasm (increased eosin binding to damaged protein, loss of ribosomes)

Plasma membrane changes

Stay intact

Loss of integrity → leak enzymes

Inflammation?

None

Yes

Markers

Leaked cellular components appear in blood

• hepatitis: transaminases
• AMI: cardiac enzymes