Introduction to Pathology

Pathology

• The study of disease (pathos) and suffering (logos).
• Focuses on changes in cells, tissues, and organs caused by disease.
• Involves laboratory examination of body tissue.
• Bridges basic sciences with clinical medicine.
• Utilizes various techniques (morphologic, molecular, microbiologic, immunologic).
• Pathologist: Physician who interprets and diagnoses disease-related changes.

Introduction to Pathology

• General Pathology: Studies cellular and tissue responses to abnormal stimuli.
  • Examples: cell injury, inflammation, repair, hemodynamic disorders, genetic disorders, immune system diseases, infectious diseases, and environmental diseases.
• Systemic Pathology: Examines alterations in specific organs and tissues in a diseased state.
  • Aspects include etiology, pathogenesis, and disease classification.
• Etiology (Cause):
  • Genetic: Mutations (congenital or acquired).
  • Acquired: Infectious, nutritional, chemical factors.
• Pathogenesis (Mechanism): The sequence of events from initial stimulus to disease manifestation.

Classification of Pathology

• Anatomical/ Surgical Pathology:
  • Gross and microscopic examination of tissues for diagnosis.
  • Includes: histopathology, cytopathology, autopsy, and subspecialties (like neuropathology).
• Clinical Pathology:
  • Involves hematology, microbiology, immunology, serology, and biochemistry.

Diagnosis in Anatomical Pathology

• Biopsies: Tissue samples for diagnosis.
  • Excisional: Removal of the entire tissue.
  • Incisional: Removal of a portion of the tissue.
• Smears: Cell samples for diagnosis.
  • Exfoliative: Obtaining cells naturally shed (e.g., Pap smear for cervical cancer screening).
  • Fine Needle Aspiration (FNA): Sampling cells using a needle (e.g., breast or thyroid).

Biopsy Types

• Fine Needle Aspiration (FNA):
  • Advantages: Easy to obtain, can be guided by ultrasound or CT, useful for peripheral adenopathy.
  • Limitations: Only obtains a few cells, limited use for certain diagnoses.
• Core Biopsy (Larger Needle):
  • Advantages: More tissue for confident diagnosis, can be used for flow cytometry (confirming lymphoma diagnosis).
  • Limitations: May not identify all lymphomas/ leukemias.
• Excisional Biopsy:
  • Advantages: Most tissue for diagnosis.
  • Limitations: More invasive, time-consuming to arrange.
• EBUS/TANA:
  • Advantages: Necessary for lung lesions inaccessible by other methods.
  • Limitations: Same limitations as FNA.

Stages of Tissue Processing

• Preservation and Processing of Tissues:
  • Specimen Identification and Labeling:
    • Each specimen receives a unique number for identification.
  • Gross Examination:
    • Initial visual inspection of the specimen.
  • Fixation:
    • Preserves the specimen using 10% formaldehyde (formalin).
  • Dehydration:
    • Removal of water using increasing concentrations of alcohol.
  • Clearing:
    • Replacement of alcohol with xylene or toluene.
  • Impregnation:
    • Infiltration of the specimen with molten paraffin.
  • Embedding:
    • Encasing the specimen in solidified paraffin.
  • Section Cutting:
    • Thin slices of embedded tissue are made.
  • Staining:
    • Staining the slices for visualization.
      • Hematoxylin-Eosin (H&E) Staining:
        • Stains nuclei blue and cytoplasm/extracellular components red.
  • Mounting:
    • Preparing the stained slices for microscopic examination.

Cellular Responses to Stress

• Basic Principles:
  • Organ: A differentiated structure (heart, liver, kidney) composed of cells and tissues.
  • Homeostasis: The normal physiological state that maintains a stable internal environment.
  • Stress on an organ can lead to cellular responses (adaptation, injury, death).
• Cellular Responses:
  • Adaptation: Reversible changes in cell size, number, and function in response to stress.
  • Injury: Reversible or irreversible damage to cells.
  • Apoptosis: Programmed cell death.
  • Intracellular Accumulation: Buildup of substances within cells.
  • Calcification: Deposition of calcium salts in tissues.
  • Cellular Aging: Changes associated with the aging process.
• Factors Determining Cellular Response:
  • Nature and Severity of Stress:
    • Fast, severe, or prolonged stress leads to cell injury.
    • Less severe stress leads to cellular adaptation.
  • Involved Cell: Cell types vary in their ability to adapt or respond to stress.

Growth Adaptations

• Adaptation: A new steady state achieved by cells in response to stress, preserving viability and function.
• Growth Adaptations:
  • Hypertrophy: Increase in cell size leading to increased organ size.
    • Mechanism: Increased production of cellular proteins and organelles.
    • Causes: Increased functional demand (workload), hormonal stimulation, growth factor stimulation.
    • Limitations: Hypertrophy has limits, excessive stress can lead to cell injury.
  • Hyperplasia: Increase in cell number leading to increased organ size.
    • Mechanism: Production of new cells from stem cells.
    • Types:
      • Physiological: Normal growth due to hormones or compensation.
      • Pathological: Excessive hormone stimulation.
    • Examples:
      • Physiological: Uterine enlargement during pregnancy (hormonal), compensatory hyperplasia after liver resection (growth factors).
      • Pathological: Endometrial hyperplasia (excessive estrogen), prostate hyperplasia (androgen).
    • Note: Pathological hyperplasia can increase cancer risk.
  • Atrophy: Decrease in cell size and number leading to decreased organ size.
    • Mechanism:
      • Decreased protein synthesis and increased protein degradation.
      • Reduced metabolic activity.
      • Ubiquitin-proteasome pathway: Degradation of cellular components.
      • Autophagy (self-eating) to find protein sources.
    • Causes: Decreased workload, loss of innervation, diminished blood supply, inadequate nutrition, loss of endocrine stimulation, aging.
    • Types:
      • Physiological: Embryonic development, involuting gravid uterus.
      • Pathological: Disuse atrophy, denervation atrophy, inadequate nutrition, loss of endocrine stimulation, aging.
  • Metaplasia: A change in cell type due to stress.
    • Mechanism: Reversible replacement of one differentiated cell type with another.
    • Example: Squamous metaplasia in the respiratory tract of smokers.

This quiz covers the fundamental concepts of pathology, including general and systemic pathology. It explores cellular responses, disease etiology, and the methods used in the diagnosis and evaluation of diseases. Perfect for anyone looking to deepen their understanding of how diseases affect the body.