1.3 - Causes and Morphology of Cell Injury

Major causes of cell injury include hypoxia/ischemia, chemicals, infections, immune reactions, genetic defects, nutritional problems, physical injury, and aging. Reversible injury results in swelling and fatty changes, while irreversible injury results in necrotic or apoptotic changes.

oxygen deprivation

• hypoxia — tissue does not receive adequate oxygen

  • examples:

    • pneumonia → fluid within alveoli impairs oxygen exchange

    • CO poisoning → CO interferes with oxygen transport by hemoglobin

• ischemia — blood supply is inadequate

  • blood delivers oxygen, so ischemia commonly produces hypoxia

  • caused by impaired arterial flow or impaired venous drainage

chemical agents

damage cells through many mechanisms

• poisons → alter membrane permeability

• innocuous substances → harmful at abnormal concentrations

  • example — excess salt can disrupt osmotic environment across cell membrane

infectious agents

• viruses

• bacteria

• fungi

• protozoa

• helminths

immunologic injury

immune system can injure the body’s own tissues

• inflammatory reactions

• autoimmunity

• hypersensitivity

genetic defects

genetic abnormalities can cause:

• deficient proteins

• abnormal proteins

• dysfunctional cellular pathways

nutritional imbalance

deficiencies and excesses can injure cells

• deficiency → inadequate nutritional access

• excess → contribute to disorders like type 2 diabetes and obesity-related disease

physical agents

• trauma

• temperature extremes

• radiation

• changes in atmospheric pressure

aging

contributes to cellular vulnerability and accumulated injury

morphology of cell injury

morphology is structural changes that can be observed in an injured cell or tissue

• biochemical dysfunction → ultrastructural changes → light microscopic changes → gross changes

• functional/biochemical abnormalities occur before obvious structural abnormalities

reversible injury morphology

1. cellular swelling:

   • decreased ATP → failure of energy-dependent pumps → Na⁺ accumulates inside → water follows Na⁺ → cell swells

   • inability to maintain ionic and fluid homeostasis

2. fatty change

   • fat accumulates inside injured cells that cannot properly metabolize lipid

   • microscopically → lipid vacuoles appear within cytoplasm

   • common in tissues involving fat metabolism, including liver and myocardium

necrosis morphology

major hallmark — loss of plasma membrane integrity

• increased eosinophilia → denatured cytoplasmic proteins bind more eosin and loss of RNA

• myelin figures → remnants of damaged cellular membranes

• calcification → calcium deposits in dead or damaged tissues, saponification of phospholipids

• nuclear changes to nucleus:

  • pyknosis → nuclear shrinkage and increased basophilia

  • karyorrhexis → fragmentation of pyknotic nucleus

  • karyolysis → fading of nuclear basophilia due to DNA degradation

apoptosis morphology

contents remain packaged, so inflammation is minimized

1. chromatin condenses

2. cell fragments into membrane-bound pieces

3. apoptotic bodies form