Chapter 2: Cellular Injury, Adaptations, and Maladaptive Changes

Adaptations: Atrophy, hypertrophy, hyperplasia, metaplasia, dysplasia —> stress removed—> normal cell restored

Reversible cell injury: degenerations, sub-cellular alterations, intracellular accumulations —> stress removed—> repair and healing

Irreversible cell injury —> cell death

  • The cell either adapts or compensates

  • cells develop maladaptive changes resulting in changes to cell function/ structure

  • cells can de

  • Cellular adaptation and maladaptive changes occur as a result of specific disease processes, altered cell function or environmental factors

Causes of cellular adaptation

  • damage to cell membrane

  • reduced levels of ATP

  • changes in metabolic processes

  • change in pH

Cellular changes: Aging

  • Decrease in cellular function

    • cell structure changes

    • mitosis slows down

    • increased accumulation of waste

    • altered protein syntheses and ATP production

    • decreased collagen and elastin fibers

  • inability to adapt to change or exposure

    • alteration in nucleus-free radicals

    • alterations in DNA during mitosis

Causes of cellular change

  • ischemia or cellular hypoxia - decreased oxygen

  • inflammation or immunological runs (autoimmune)

  • nutrition imbalance

  • fluid and electrolyte disturbances

  • microorganisms

  • free radical injury

  • physical agents

  • genetic defects

Normal alterations - hypertrophy or atrophy

  • Hypertrophy- enlargement of tissue mass due to the increased size of cells

    • normal physiologic hypertrophy- increased stimuli (workload)

    • Pathologic hypertrophy- cardiomyopathy

  • atrophy- decreased tissue mass- cells become smaller

    • disuse or decreased metabolic need

    • decrease in blood flow- ischemia

    • lack of nerve stimulation

    • loss of hormonal stimulation

    • aging

Abnormal alterations (pathologic) leads to cell death

  • DNA changes- ionizing radiation

  • Trauma or chemical exposure

hyperplasia- overproduction of cells (pregnancy)

metaplasia- mature cell replaced by another mature cell

dysplasia- cells vary in size and shape within a tissue type, increased rate of mitosis; often due to chronic irritation, infection, or precancerous change

neoplasia- new growth, tumor

Endothelial Cell Injury

  • Endothelium= lining of arterial blood vessels

  • Body larges organ → injury causes widespread effects

  • Causes

    • Hypertension (HTN → shearing injury, weakening of vessel walls

    • Diabetes mellitus (DM)→ hyperglycemia causes chemical damage to endothelial cells but also narrowing of the arteries (vasoconstriction)

    • smoking→ arteriosclerosis and vasoconstriction

    • angiotensin II → vasoconstriction

  • Effects: atherogenesis (deposition of plaque within arteries)

Hypoxia- Most common cause of cell injury

  • due to ischemia or reduced blood supply to the issue

  • Causes- inadequate oxygen intake(high altitude, pulmonary disease), anemia, cardiac arrest, poor circulation, or obstruction of blood flow(arteriosclerosis, thrombosis)

Results of cellular Hypoxia

  • inability to produce ATP

  • failure of NA+ and K+ pump

  • Ca++ flooding of cell

  • cellular swelling

  • protein synthesis slows/stops

  • cellular hypoxia→ anaerobic metabolism → 2 ATP and pyruvic acid (lactic acid)

  • cell dies

Impact on tissue from hypoxia

  • Infarction = death of tissue due to prolonged ischemia (ischemic necrosis

  • individual cell types have varying tolerance levels to ischemia

    • brain & heart cells infarct within minutes

    • skeletal muscles can last for hours

Apoptosis: cell death; programmed cell death

  • eliminated unwanted, unnecessary, or damaged cells without any adverse effects

  • can be either normal or due to disease

  • if doesn’t occur at approximate times, can lead to excess accumulation or excessive distraction

Necrosis= cell death caused by injury

  • cell degraded by autolysis(break apart)

Complications of necrosis

  • gangrene= infection of necrotic tissue

    • caused by Clostridium perfringens

    • most commonly occurs in necrotic tissues of lower extremities caused by PAD

      • emits a gas within the tissues

      • often requires amputation