Cell Injury and Responses

Cell Injury

• Cell injury is a fundamental process in pathology, encompassing a spectrum of responses that range from reversible alterations to irreversible cell death.
• Stimuli causing cell injury include hypoxia, toxins, infectious agents, immunologic reactions, and genetic defects.
• Cell injury mechanisms disrupt essential cellular functions.

Cellular Responses to Injury

• Reversible injury: Early stages involve reversible changes like cellular swelling, cytoplasmic vacuolation, and mitochondrial swelling.
• Irreversible injury: Persistent or intensified stimuli lead to irreversible injury and cell death.
• Mechanisms of cell injury:
  • Depletion of ATP
  • Mitochondrial damage
  • Loss of membrane integrity
  • Defects in intracellular calcium homeostasis
  • Oxidative stress
  • Protein misfolding and aggregation

Types of Cell Death

• Necrosis: Accidental cell death with loss of membrane integrity and release of cellular contents, characterized by inflammation.

  • Types of necrosis:
    • Coagulative necrosis: Common in hypoxic tissue injury.
    • Liquefactive necrosis: Tissue digestion by enzymes from inflammatory cells, often from bacterial infections.
    • Caseous necrosis: Soft, cheesy appearance, seen in tuberculous granulomas.
    • Fat necrosis: Localized fat destruction due to pancreatic enzyme release.

• Apoptosis: Programmed cell death for development, homeostasis, and elimination of unwanted cells; marked by specific biochemical events without inflammation.

  • Apoptosis mechanisms:
    • Activation of caspases, a family of proteases
    • DNA fragmentation
    • Membrane blebbing and formation of apoptotic bodies
    • Phagocytosis of apoptotic bodies by neighboring cells

Pathological Consequences of Cell Injury

• Inflammation: Body's response to injury, involving vascular changes, cellular infiltration, and tissue repair.
• Tissue repair: Processes restoring tissue architecture and function after injury.
• Fibrosis: Excessive connective tissue deposition, causing scarring.
• Gangrene: Extensive tissue death due to severe ischemia or infection.
  • Types of gangrene:
    • Dry gangrene
    • Wet gangrene
    • Gas gangrene

Cellular Adaptations

• Hypertrophy: Increased cell size.
• Hyperplasia: Increased cell number.
• Atrophy: Decreased cell size.
• Metaplasia: Transformation of one cell type to another, a response to stress.

Hypoxic Cell Injury

• Hypoxia, a lack of oxygen, is a common cause of cell injury.
• Hypoxia decreases ATP production, a critical cellular energy source.
• Progressive hypoxia impairs cellular processes, eventually leading to cell death.

Toxic Injury

• Exposure to endogenous or exogenous substances causes direct or indirect toxic injury to cells.

Summary of Key Concepts

• Cell injury is a range of responses to stimuli, from reversible to irreversible death including necrosis and apoptosis.
• Necrosis is inflammatory while apoptosis is not.
• Consequences include inflammation, repair, fibrosis, and gangrene.
• Cellular adaptations, like atrophy, hypertrophy, and metaplasia, are responses to stress.
• Hypoxia and toxins are common causes of cell injury.

This quiz explores the concepts of cell injury and the various cellular responses to it, including reversible and irreversible injury mechanisms. Gain insights into the factors that contribute to cell injury and the pathways involved in disrupting cellular functions. Perfect for students studying pathology and cellular biology.