Cell Injury Basics😊

Cell Injury Basics

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  • Most Common Cause of Cell Injury:
    • Hypoxia 
  • Most Common Cause of Hypoxia:
    • Ischemia 
  • Cell Sensitivity to Hypoxia:
      • Sensitivity
      Cells
      Time
      Most Sensitive
      Neurons (brain tissue)
      give way in 2-5 minutes.
      Most Resistant
      Fibroblasts 
      withstand 30-60 minutes
  • Types of Cell Injury:
    • Reversible cell injury
    • Irreversible cell injury
      • Type of Injury
      Characteristic Features
      Reversible Cell Injury
      - Cellular swelling/hydropic change (1st m/c morphological feature)
      - m/c organelle affected: Mitochondria
      -       Bleb formation
      -       Loss of microvilli
      - Chromatin clumping
      Irreversible Cell Injury
      Electron microscopy:
      Amorphous densities in mitochondria

      Light microscopy:
      Nuclear changes
      → Pyknosis: Chromatin clumping
      →       Karyolysis: Dissolution
      →       Karyorrhexis: Fragmentation

      Myelin figures (Irreversible > reversible injury)
  • Mnemonic:
    • Reversible →
      • Riveril Vellam → Reversible → Hydropic change
      • Riveril Myil (Myelin) vallapozhum (not main) varum
    • Irreversible → Amorphous, nuclear, myelin
  • Mitochondria
    • Most important organelle affected in
        1. Apoptosis
        1. Reversible cell injury
        1. Calcification

Reversible Cell Injury

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  • Decreased oxygen → Mitochondrial dysfunction (first change of cell injury) → ↓ ATP production → 3 changes
      1. Sodium-Potassium ATPase Pump Failure (NOKIa) → 3 Naâș enter, 2 Kâș exit → Water influx → Cellular swelling (hydropic change) → Myelin Figures Formed
      1. Hypoxia → Anaerobic Glycolysis → ↑Lactic acid → ↓pH → Nuclear chromatin clumping (second change of cell injury)
      1. Ribosomes detach from RER → ↓ protein synthesis → third change

Myelin Figures:

  • Formed as cells swell and burst.
      • notion image
  • Composition:
    • Primarily phospholipid
    • with a little calcium.
  • Presence:
    • Seen in reversible injury (process starts)
    • More enhanced in irreversible cell injury.
  • Microscopic Appearance: 
    • Lamellated concretions 
    • under electron microscopy

Irreversible Cell Injury

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Two Defining Moments:

  • Mnemonic: M&M
      1. Membrane damage
      1. Mitochondrial Damage

Membrane damage + Mitochondrial damage → Calcium influx

  1. Into mitochondria → Amorphous densities formed

      2. Amorphous Densities 
      (or amorphous flocculent densities):

      • Composition: Calcium.
      • Location: Seen inside the mitochondria.
      • Injury Type: Exclusively seen in irreversible cell injury.
  1. Into cytoplasm → Activate enzymes → Phospholipase, Proteases, Nucleases → Nuclease cause Nuclear changes → Order: PKK (Pyknosis → Karyorrhexis → Karyolysis)
    1. Pyknosis (P):
        • Nucleus undergoes shrinkage and condensation;
        • appears dark and central.
    2. Karyorrhexis (K):
        • Nucleus fragments or breaks into pieces
        • likened to "bomb blast"
    3. Karyolysis (K):
        • Nucleus is gone or dissolved
        • no nucleus visible.
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