Cellular Injury

Question 1

Major causes of cell injury?

Answer 1

• Congenital causes - exposure to damaging agents during intrauterine life.
• Acquired causes e.g defective nutrition, hypoxia, chemicals or drugs, physical and mechanical causes.
• Aging

Question 2

What is the main early sign of Reversible cell injury?

Answer 2

Acute cellular swelling ( hydropic change).

Question 3

Outline the major signs that denote reversible cell injury.

Answer 3

• Vacuolar degeneration- seen as clear vacuoles on light microscope. Represent distended and pinched off segments of the endoplasmic reticulum.
• Endoplasmic reticulum dilation and degranulation.
• Dissociation of polyribosomes into single ribosomes ( seen on Electronic microscopy ) .
• Cytoplasm of injured cells appears red ( eosinophilic) in H&E stains - due to loss of RNA which usually binds the blue hematoxylin dye.
• Mitochondrial changes e.g swelling and appearance of small amorphous densities.

Question 4

Describe the mechanism by which hydropic changes occur in reversible cell injury.

Answer 4

• Ischaemia results in hypoxia causing reduced ATP production hence the cell switches to anaerobic glycolysis. This causes build up of lactic acid, causing failure of the Sodium pump that results in inflow of water.
• Breakdown of cell constituents results in intracellular water accumulation through osmosis.
• Direct plasma membrane injury can also result in increased permeability.

Question 5

Outline the cell surface changes seen in reversible cell injury.

Answer 5

• Loss of microvilli - may reappear if cell recovers.- blunting may also occur.
• Surface blebs.
• Accumulation of myelin figures due to degenerating lipid membranes - tested using special stains for lipid content - composed of phospholipids derived from damaged cellular membranes.

Question 6

What are the nuclear changes that are evident in reversible cell injury?

Answer 6

• Mild clamping of chromatin.
• Separation of nucleolus into fibrillar and granular components.

Question 7

List the major changes that are seen in Irreversible cell injury.

Answer 7

• Severe vacuolations.
• Woody or flocculent density in mitochondria.
• Plasma membrane damage with loss of intracellular substance into extracellular space.

Question 8

Which is the most reliable early sign of irreversible cell injury?

Answer 8

Woody or flocculent density in mitochondria.

Question 9

Describe the cytoskeletal changes which are usually evident in Irreversible cell injury.

Answer 9

• Breakage of microfilaments and intermediate filaments.
• Perturbation of membrane skeleton, resulting in formation of surface blebs.
• Drop in PH leading to leakage of lysosomal enzymes and their activation in the cytosol e.g proteases, nucleases, glucosidases.
• Autolysis from the leaked lysosomal enzymes resulting in dead cells and membranes that can be phagocytosed by macrophages and neighbouring cells.

Question 10

What are the biochemical mechanisms involved in plasma membrane disruption?

Answer 10

• ATP depletion e.g in ischaemic and toxic injury.
• Exhaustion of protective mechanisms that mop up free radicals leads to imbalance and oxidative stress – damage.
  — Oxygen & Oxygen derived radicals generate energy which results in reduction of molecular oxygen into water.
• Increased intracellular calcium levels results in increased membrane permeability.
• May also be caused by direct cell injury by infectious agents , Complement system , physical and chemical agents.

Question 11

Outline the possible causes of irreversible mitochondrial damage.

Answer 11

• Oxidative stress.
• Breakdown of phospholipids.
• Increase in cytosolic calcium .
• Accumulation of lipid breakdown products.
  – Irreversible mitochondrial damage may lead to irreversible cell injury.

Question 12

What is the difference between necrosis and apoptosis?

Answer 12

Necrosis refers to the spectrum of morphological changes following cell death in living tissues while apoptosis…

Question 13

Outline the major morphological changes associated with Necrosis.

Answer 13

• Cells show increased eosinophilia with H&E stains - this is due to loss of cytoplasmic RNA & accumulation of denatured cytoplasmic proteins which bind to the red eosin dye.
• Glassy homogeneous appearance due to loss of glycogen particles.
• Vacuolated moth eaten appearance - due to enzymatic digestion of organelles.
• Dystrophic calcification - occurs due to deposition of calcium salts and other minerals on necrotic cells resulting in their calcification.

Question 14

Describe the electron microscopy changes associated with Necrosis.

Answer 14

• Dissociation/ discontinuities of plasma and organelle membranes.
• Dilation of mitochondria with appearance of large amorphous densities.
• Intracytoplasmic myelin figures.
• Amorphous osmophilic debris which are aggregates of fluffy material representing dentured protein .

Question 15

What are the major nuclear patterns related to DNA breakdown associated with Necrosis?

Answer 15

• Karyolysis - fading basophilia of chromatin - reflects loss of DNA because of enzymatic degradation by endonucleases.
• Pykinosis- nuclear shrinkage and increased basophilia - chromatin condenses into a dense, shrunken basophilic mass.
• Karryorrhexis - pykinotic or partially pykinotic nucleus undergoes fragmentation.
• With time the nucleus of the necrotic cell totally disappears.

Question 16

List down the major forms of Necrosis, stating their distinguishing feature.

Answer 16

• Coagulative necrosis - architecture of dead tissues is preserved for some days before being broken down by lysosomal enzymes.
• Liquifactive / colliquative necrosis - digestion of dead cells resulting in transformation of tissue into a viscous liquid ( focal bacterial and fungal infections).
• Gangrenous necrosis - e.g when a limb loses its blood supply , undergoes coagulative necrosis, then undergoes liquefactive necrosis when bacterial infection is superimposed.
• Caseous necrosis
• Fat necrosis
• Fibrinoid necrosis

Question 17

Outline the Electron Microscopy changes evident in Apoptosis.

Answer 17

• Cell shrinkage.
• Dense cytoplasm and tightly packed organelles.
• Chromatin condensation - chromatin material aggregates peripherally under the nuclear membrane into dense masses of various shapes & sizes.
• Nucleus may break down into fragments.
• Formation of cytoplasmic blebs & apoptotic bodies.
• Phagocytosis of apoptotic cells or cell bodies by macrophages and adjacent healthy cells.

Question 18

Outline the major differences between Necrosis & Apoptosis.

Answer 18

• In Necrosis, the cell is enlarged while in Apoptosis the cell shrinks in size.
• In Necrosis, nuclear changes include Pykinosis, Karryorrhexis and Karyolysis while in Apoptosis, the nucleus fragments into nucleosome sized fragments.
• In Necrosis, plasma membrane is disrupted while in Apoptosis, plasma membrane is intact with slight alterations in lipid orientation.
• In Necrosis, adjacent inflammation is frequent while in Apoptosis there is no inflammation.
• Necrosis has an invariably pathologic role while Apoptosis may have a physiological role e.g eliminating unwanted cells.

Question 19

Outline the major causes of Cellular injury.

Answer 19

• Oxygen deprivation e.g due to ichemia, cardiorespiratory failure or reduces oxygen carrying capacity of blood.
• Physical agents e.g mechanical trauma, radiation, shock & temperature extremes.
• Chemical agents and drugs , poisons e.g cyanide , arsenic & mercury, pollutants & insecticides.
• Infectious agents e.g bacteria & fungi.
• Immunologic reactions to external agents, and endogenous self antigens ( auto immune disorders).
• Genetic abnormalities.
• Nutritional imbalances.