pathology; intro block

• Modification of growth


  • Introduction
  • Hypertrophy
  • Hyperplasia
  • Atrophy
  • Metaplasia
  • Dysplasia
• Labile cells


  Undergo frequent division in life to replace those lost through differentiation, called continuous replicators (e.g. cells of lymph nodes, skin, endometrium, cell linings of alimentary canal and respiratory system)
• Stable cells


  Also called discontinuous replicators, can divide when stimulated but are usually in the quiescent stage (e.g. liver, kidney, pancreas, endocrine glands, and fibroblasts)
• Permanent cells


  Cannot divide, also called non-replicators (e.g. neurons, skeletal and cardiac muscles)
• Cell growth


  Process of increase in size and mass of a cell resulting from synthesis of specific cell components
• Cell differentiation


  Process by which a cell developed overt specialised morphology or function which distinguishes it from its parent cell
• Abnormalities of cellular growth

  • Excesses - hypertrophy and hyperplasia
  • Decreases - agenesis and hypoplasia
  • Acquired after full development - atrophy and aplasia
• Adaptation


  Reversible changes in the size, number, phenotype, metabolic activity or functions of cells in response to change in their environment
• Abnormalities of cellular differentiation

  • Metaplasia
  • Dysplasia
• Hypertrophy


  Increase in size of an organ or tissue due to increase in size of its constituent specialised cells
• Hypertrophy


  • Can be physiologic or pathologic
  • Physiologic causes: increased functional demand or workload, stimulation by hormones
  • Pathologic causes: adaptive, compensatory or hormonal
• Pathologic hypertrophy


  • Cardiac enlargement in response to increased workload in hypertension
  • Stomach in pyloric stenosis
  • Urinary bladder in case of urethral stricture
  • Compensatory enlargement of a kidney when one is absent or surgically removed
  • Hormonal hypertrophy in gigantism and acromegaly
• Mechanism of hypertrophy


  Gene activation, protein synthesis, and production of cellular organelles
• Hyperplasia


  Increase in size of an organ or tissue due to an increase in the number of its specialised constituent cells, involves production of new cells from stem cells
• Hyperplasia and hypertrophy are distinct processes but frequently occur together and may be triggered by the same external stimulus
• Hyperplasia can only occur if the cells are capable of dividing
• Types of hyperplasia


  • Physiologic - hormonal, compensatory
  • Pathologic - caused by excessive or inappropriate actions of hormones or growth factors
• Physiologic hyperplasia


  • Pubertal enlargement of the female breast
  • Regeneration of the liver following partial hepatectomy
  • Bone marrow activity/hyperplasia in response to acute blood loss
• Pathologic hyperplasia


  • Endometrial hyperplasia
  • Benign prostatic hyperplasia (BPH)
• Pathologic hyperplasia can lead to dysplasia and cancer but BPH is an exception
• Hyperplasia in viral infections

  • Skin warts in HPV infection, virus makes factors that interfere with host proteins that regulate cell proliferation
• Atrophy


  Reduction in the size of an organ or tissue due to a decrease in cell size and number
• Types of atrophy


  • Physiological - in foetus, infancy, later life
  • Pathological - generalised, localised (ischaemic, pressure, disuse, neuropathic, idiopathic)
• Causes of atrophy


  • Decreased workload
  • Loss of innervation
  • Diminished blood supply
  • Senile atrophy due to atherosclerosis
  • Inadequate nutrition
  • Loss of endocrine stimulation
  • Pressure
• Mechanism of atrophy


  Decreased protein synthesis and increased protein degradation in cells, decrease in cell number via apoptosis and autophagy, increased protein degradation via ubiquitin-proteasome pathway
• Metaplasia


  Reversible change in which one differentiated cell type (epithelial or mesenchymal) is replaced by another cell type
• Epithelial metaplasia


  • Columnar to squamous in respiratory tract in response to chronic irritation (e.g. cigarette smoking)
  • Squamous to columnar in Barrett's oesophagus
• Advantage of epithelial metaplasia

  Epithelium becomes tough and can withstand stress
• Disadvantage of epithelial metaplasia

  Inherent abilities/functions are lost (e.g. respiratory epithelium's ability to protect against infections, produce mucus secretions, and perform ciliary actions)
• Malignant transformation is a possibility in epithelial metaplasia
• Connective tissue metaplasia


  • Formation of bone, cartilage or adipose tissue in tissue that does not normally contain these elements (e.g. myositis ossificans)
• Mechanism of metaplasia


  Result of reprogramming of stem cells that exist in normal tissue, or of undifferentiated mesenchymal cells present in connective tissue
• Dysplasia


  Disordered growth, occurs mainly in epithelia, involves loss of uniformity of individual cells and loss in their architectural orientation
• Changes in dysplasia


  • Anisocytosis
  • Poikilocytosis
  • Hyperchromatism
  • Presence of mitotic figures
• Dysplasia may be a precursor to malignant transformation, but dysplasia may not necessarily progress to cancer
• Carcinoma in-situ and invasive carcinoma

  Dysplasia involving the entire epithelium is referred to as carcinoma in-situ, and invasive carcinoma when it has breached the basement membrane
• Dysplasia often occurs in metaplastic epithelium but not all metaplastic epithelium is dysplastic