FOCUS NOTES — PATHOPHYSIOLOGY
1. CELLULAR ORGANELLES, MEMBRANE TRANSPORT
& IONS
Cellular Organelles
● Nucleus: Contains DNA; controls gene expression, replication, and transcription.
● Nucleolus: Produces rRNA and ribosomal subunits.
● Ribosomes: Protein synthesis; free ribosomes make intracellular proteins, attached
ribosomes make secreted/membrane proteins.
● Rough ER: Protein production and transport.
● Smooth ER: Lipid/steroid production, detoxification, Ca²⁺ storage.
● Golgi: Modifies, sorts, and packages proteins/lipids.
● Mitochondria: Produce ATP through aerobic metabolism.
● Lysosomes: Digest damaged organelles, proteins, and cellular debris.
● Peroxisomes: Fatty-acid breakdown and detoxification.
● Cytoskeleton: Cell shape, support, and intracellular movement.
● Centrioles: Organize microtubules during cell division.
Membrane Transport
● Simple diffusion: High → low concentration; no ATP. Example: O₂, CO₂.
● Facilitated diffusion: High → low through membrane proteins; no ATP. Example:
glucose.
● Osmosis: Water moves toward higher effective solute concentration.
● Filtration: Movement caused by hydrostatic pressure; example: kidney glomerulus.
● Active transport: Uses energy to move against a gradient. Example: Na⁺/K⁺ pump
moves 3 Na⁺ out and 2 K⁺ in.
● Endocytosis: Brings substances into the cell.
○ Phagocytosis: Large particles/bacteria.
○ Pinocytosis: Fluid.
○ Receptor-mediated: Specific substances such as LDL.
● Exocytosis: Releases substances outside the cell; example: hormones and
neurotransmitters.
Major Ions
● Intracellular: K⁺, Mg²⁺, phosphate, proteins.
● Extracellular: Na⁺, Ca²⁺, Cl⁻, HCO₃⁻.
, ● Remember: K⁺ = inside; Na⁺ = outside.
2. CELLULAR INJURY & ADAPTATION
Hypoxia vs Ischemia vs Infarction
● Hypoxia: Inadequate oxygen.
● Ischemia: Inadequate blood flow → ↓O₂/nutrients + impaired waste removal.
● Infarction: Tissue death from prolonged ischemia.
Cell Death
● Necrosis: Pathologic cell death; membrane ruptures and contents leak → inflammation.
● Gangrene: Extensive tissue necrosis.
○ Dry: Ischemic tissue.
○ Wet: Necrosis + infection.
○ Gas: Bacterial infection producing gas.
● Apoptosis: Controlled/programmed cell death; cell shrinks and fragments without
significant inflammation.
Cellular Adaptations
● Hypertrophy: ↑ cell size; example: cardiac muscle with hypertension.
● Hyperplasia: ↑ cell number.
● Atrophy: ↓ cell size from disuse, poor nutrition, reduced blood supply, aging, etc.
● Metaplasia: One mature cell type changes to another better suited to stress; often
reversible.
● Neoplasia: Uncontrolled abnormal cell growth; may be benign or malignant.
Oxygen Deprivation
↓O₂ → ↓ATP → Na⁺/K⁺ pump failure → Na⁺ + water enter cell → swelling → anaerobic
metabolism → lactic acid ↑ → pH ↓ → Ca²⁺ accumulates → enzyme/membrane damage →
mitochondrial and lysosomal injury → necrosis if severe.
● Autolysis: Cell digests itself using its own lysosomal enzymes.
● Heterolysis: Other cells, especially WBCs, digest damaged/dead tissue.
● Cellular edema: Usually from ATP depletion and Na⁺/K⁺ pump failure.
● Cellular dehydration: Water leaves cells when extracellular fluid becomes hypertonic,
such as hypernatremia.
● Reperfusion injury: Restoring blood flow after ischemia can cause additional damage
from ROS, Ca²⁺ overload, mitochondrial injury, and inflammation.
1. CELLULAR ORGANELLES, MEMBRANE TRANSPORT
& IONS
Cellular Organelles
● Nucleus: Contains DNA; controls gene expression, replication, and transcription.
● Nucleolus: Produces rRNA and ribosomal subunits.
● Ribosomes: Protein synthesis; free ribosomes make intracellular proteins, attached
ribosomes make secreted/membrane proteins.
● Rough ER: Protein production and transport.
● Smooth ER: Lipid/steroid production, detoxification, Ca²⁺ storage.
● Golgi: Modifies, sorts, and packages proteins/lipids.
● Mitochondria: Produce ATP through aerobic metabolism.
● Lysosomes: Digest damaged organelles, proteins, and cellular debris.
● Peroxisomes: Fatty-acid breakdown and detoxification.
● Cytoskeleton: Cell shape, support, and intracellular movement.
● Centrioles: Organize microtubules during cell division.
Membrane Transport
● Simple diffusion: High → low concentration; no ATP. Example: O₂, CO₂.
● Facilitated diffusion: High → low through membrane proteins; no ATP. Example:
glucose.
● Osmosis: Water moves toward higher effective solute concentration.
● Filtration: Movement caused by hydrostatic pressure; example: kidney glomerulus.
● Active transport: Uses energy to move against a gradient. Example: Na⁺/K⁺ pump
moves 3 Na⁺ out and 2 K⁺ in.
● Endocytosis: Brings substances into the cell.
○ Phagocytosis: Large particles/bacteria.
○ Pinocytosis: Fluid.
○ Receptor-mediated: Specific substances such as LDL.
● Exocytosis: Releases substances outside the cell; example: hormones and
neurotransmitters.
Major Ions
● Intracellular: K⁺, Mg²⁺, phosphate, proteins.
● Extracellular: Na⁺, Ca²⁺, Cl⁻, HCO₃⁻.
, ● Remember: K⁺ = inside; Na⁺ = outside.
2. CELLULAR INJURY & ADAPTATION
Hypoxia vs Ischemia vs Infarction
● Hypoxia: Inadequate oxygen.
● Ischemia: Inadequate blood flow → ↓O₂/nutrients + impaired waste removal.
● Infarction: Tissue death from prolonged ischemia.
Cell Death
● Necrosis: Pathologic cell death; membrane ruptures and contents leak → inflammation.
● Gangrene: Extensive tissue necrosis.
○ Dry: Ischemic tissue.
○ Wet: Necrosis + infection.
○ Gas: Bacterial infection producing gas.
● Apoptosis: Controlled/programmed cell death; cell shrinks and fragments without
significant inflammation.
Cellular Adaptations
● Hypertrophy: ↑ cell size; example: cardiac muscle with hypertension.
● Hyperplasia: ↑ cell number.
● Atrophy: ↓ cell size from disuse, poor nutrition, reduced blood supply, aging, etc.
● Metaplasia: One mature cell type changes to another better suited to stress; often
reversible.
● Neoplasia: Uncontrolled abnormal cell growth; may be benign or malignant.
Oxygen Deprivation
↓O₂ → ↓ATP → Na⁺/K⁺ pump failure → Na⁺ + water enter cell → swelling → anaerobic
metabolism → lactic acid ↑ → pH ↓ → Ca²⁺ accumulates → enzyme/membrane damage →
mitochondrial and lysosomal injury → necrosis if severe.
● Autolysis: Cell digests itself using its own lysosomal enzymes.
● Heterolysis: Other cells, especially WBCs, digest damaged/dead tissue.
● Cellular edema: Usually from ATP depletion and Na⁺/K⁺ pump failure.
● Cellular dehydration: Water leaves cells when extracellular fluid becomes hypertonic,
such as hypernatremia.
● Reperfusion injury: Restoring blood flow after ischemia can cause additional damage
from ROS, Ca²⁺ overload, mitochondrial injury, and inflammation.
