Pathophysiology - Cell Injury

Cell Injury

1. Physical Agents:
• Mechanical Forces
• Split, tear, fracture, injured blood vessels
• Extremes of temperature
• Heat – vascular injury, acceleration of cell metabolism, inactivates  temperature-sensitive enzymes, disrupts cell membrane
• Cold – increases blood viscosity, vasoconstriction, hypoxic tissue injury
• Electrical injuries
• Extreme tissue injury and disruption of neural and cardiac impulses
• Lightning: most severe damage
• Ionizing radiation injury
• Causes ionization of molecules and atoms in the cell, release of free radicals that interact with critical cell components resulting to cell death and interrupted cell replication (swelling, disruption of organelles, cell membrane alterations, marked changes in the nucleus)
• Rapidly dividing cells of the bone marrow and intestines are more vulnerable
• Skin cancer, leukemia, lung cancer
• Ultraviolet radiation
• Sunburn: increases rate of skin cancer
• Damage to melanin-producing processes on the skin
• Non-ionizing radiation
• Infrared UTZ, microwaves, laser energy
• Causes variations and rotation of atoms and molecules
• Subcutaneous tissue injury
2. Chemical injury
1. Drugs
2. Lead toxicity
1. Flaking paint, lead-contaminated dust and soil, root vegetables, water pipes, pottery
2. Pottery makers, miners, workers, welders, storage battery workers, newsprint workers
3. Stored in bones and teeth (85%) – gingival margins
4. Inactivates enzymes, competes with calcium for incorporation into the bones, interfere with nerve transmission and brain development, compete with enzymes required  for haemoglobin synthesis
5. Acute encephalopathy
3. Biologic agents injury
• From viruses to large parasites
• Replicate and continue injuring cells (exotoxins that interfere with production of ATP, increases capillary permeability)
4. Injury from nutritional imbalances
• Excesses/ deficiencies of nutrients, vitamins, minerals
5. Free radical injury
• Atom – outer orbits are filled with paired electrons to balance their spin
• Free radical – single unpaired electron, bproduct of normal cell reactions
• Highly unstable, reacts with cell constituents causing chain reactions and more free radicals
• Damages cell membrane, inactivation of enzyme systems, damage to nucleic acid that makes up DNA
• Attacks when cells experience hypoxia (breakdown of cell protection)
• Defense: vitamin C,E,B carotene (antioxidants)
6. Hypoxic cell injury
• Interrupts oxidative metabolism and generation of ATP
7. Impaired calcium homeostasis
• Increased intracellular calcium activates enzymes with potentially damaging effects to organelles