Introduction to Pathology

Introduction to Pathology

• Pathology is the study of disease.
• "Pathos" refers to suffering or disease.
• Disease is an abnormal variation in the structure or function of any body organ or tissue.

Important Concepts in Pathology

• The core of pathology includes four aspects of a disease process:
  • Etiology: the causes of a disease
  • Pathogenesis: the mechanisms of disease development
  • Morphologic changes: the structural alterations in cells and organs
  • Clinical significance: the functional consequences of these changes

Classification and Divisions of Pathology

• Pathology is a bridging discipline, combining basic science and clinical practice.

• Types of pathology include:

  • Human pathology: encompassing autopsy, biopsy, and cytology
  • Experimental pathology

• Divisions of pathology include:

  • General pathology: focusing on the basic cellular and tissue responses to abnormal stimuli, which underlie all diseases.
  • Systemic pathology: describing specific responses of specialized organs and tissues to defined stimuli.

Cell Injury and Cellular Adaptations

• The basis of all diseases is injury to cells.
• A normal cell is typically in a steady state maintaining physiological balance based on adaptive mechanisms.
• Cell injury is of two types: reversible or irreversible.
  • Reversible injury:
    • Hydropic swelling or excess water in the cell
    • Fatty change: fat accumulation
    • Oxidative phosphorylation reduction: less ATP.
  • Irreversible injury:
    • Necrosis or overall cell death
    • Apoptosis or programmed single cell death

Causes of Cell Injury

• Hypoxia: oxygen deprivation
• Biological agents: bacteria, viruses, fungi, parasites
• Chemical agents: strong alkalis or acids, insecticides, alcohol, narcotics, air pollutants.
• Physical agents: extreme heat or cold, radiation, mechanical trauma, electric injury
• Endogenous toxins: uremia, jaundice, diabetic ketosis
• Immunological reactions and autoimmune diseases
• Nutritional imbalances: protein-calorie malnutrition, starvation, obesity, diabetes, vitamin deficiencies.
• Genetic abnormalities

Cellular Adaptation

• Cellular adaptation is a response to excessive physiological or pathological stimuli, without compromising cell viability, by modulating its functions.
• Etiology of cellular adaptations include:
  • Increased physiological demands.
  • Minor stresses
  • Reduced demands
  • Malnutrition

Types of Cellular Adaptations

• Hypertrophy: increase in cell size
• Hyperplasia: increase in cell number
• Atrophy: decrease in cell size and function
• Metaplasia: conversion of one adult cell type to another

Hyperplasia

• Physiologic hyperplasia: increase in cell number due to hormonal stimulation or functional demands.
• Pathologic hyperplasia: increase in cell number due to abnormal stimuli (e.g., excessive hormone, viral infection, chronic injury) potential to be precursors for cancer.

Atrophy

• Physiological atrophy occurs during aging, menopause, or after delivery as well as disuse.
• Pathological atrophy is caused by several factors, including disease, denervation, reduced blood supply, nutritional deficiency, reduced endocrine stimulation, and pressure.

Metaplasia

• Metaplasia is the reversible replacement of one mature cell type by another.
• Metaplasia can be a protective response.
• Metaplasia may frequently be a precursor to malignancy.