cell adaptation

• Cells respond to stress placed upon them to maintain their structure and function to keep the cell alive
• Cells can be exposed to various stresses like workload, hormonal changes, pH changes, nutritional changes, exposure to chemicals, irritants, inflammation
• Cell adaptation is crucial for maintaining homeostasis and cell survival
• Cell injury can occur due to stresses like mechanical trauma, chemical trauma, physical trauma, reduction in oxygen
• Cells can recover from injury through wound repair, regeneration, resolution, replication, or replacement of cell types
• Reversible injury allows cells to return to normal homeostasis, while irreversible injury leads to cell death
• Types of cell death include necrosis and apoptosis
• Cells can adapt to stress through atrophy, hypertrophy, hyperplasia, metaplasia, and dysplasia
• Cells are categorized into labile cells (constantly replicating), stable cells (quiescent but can replicate if needed), and permanent cells (cannot replicate)
• Atrophy:

  • Reduction in cell size due to decreased work demands, hormonal stimulation, growth factors
  • Examples: disuse, denervation, reduction in nutrition, blood flow
  • Can be physiological (normal response) or pathophysiological (disease-related)
  • Examples: muscles in the uterus after pregnancy, ischemia, denervation
• Hypertrophy:

  • Increase in cell size due to mechanical force, stretch, muscle contraction, hormonal or growth factor stimulation
  • Examples: muscle growth from weightlifting, uterus in pregnancy, bladder in response to restricted flow
  • Can be physiological or pathophysiological
  • Example: cardiac myopathies leading to heart muscle enlargement
• Hypertrophy:

  • Muscle gets bigger and longer in length proportional to width
  • Heart becomes inefficient and ineffective
  • Problem with contraction
• Hypertrophic cardiomyopathy:

  • Muscle becomes bulky
  • Restricts heart's ability to pump or fill
  • Can lead to disease
• Hypertrophy can be physiological or pathophysiological

  • Usually occurs in permanent cell types like muscle cells
• Hyperplasia:

  • Increase in cell number, not cell size
  • Occurs in labile or stable cells like epithelial cells, hemopoietic stem cells, liver cells
• Physiological hyperplasia examples:

  • Breast tissue during puberty or pregnancy
  • Liver cells becoming active when part of the liver is removed
• Pathological hyperplasia examples:

  • Prostate gland in response to androgen hormones
  • Warts caused by papilloma virus
• Metaplasia:

  • Change in cell type or morphology in response to chronic irritation or inflammation
  • Reversible adaptation
  • Examples: stomach-like cells in lower pH environment, stratified squamous cells in response to cigarette smoke
• Dysplasia:

  • Disordered growth in response to chronic irritation or inflammation
  • Increase in cell number and shape disorganization
  • Precursor for cancer
  • Examples: cervical dysplasia due to HPV, bronchopulmonary dysplasia in preterm infants
• Dysplasia can be reversible but less likely

  • Usually indicates progression towards a cancerous state