Introduction to Pathology: Key Concepts

Introduction to Pathology

• Pathology is the scientific study of disease, examining how molecules, cells, tissues, organs, or systems respond to harmful agents.
• Pathology acts as a bridge between preclinical sciences (anatomy, physiology) and clinical medicine.
• The Royal College of Pathologists defines pathology as "the science behind cure."

Key Aspects of Pathology

• Pathology studies the patterns, causes, mechanisms, and effects of illnesses.
• It interprets symptoms and identifies a range of abnormalities in organs or systems.
• Pathology forms the basis of differential diagnosis (approximately 70% of cases).

Branches of Pathology

• Histopathology (anatomical): examines tissues for changes.
• Haematology: deals with blood and blood-forming organs.
• Clinical Chemistry: analyzes chemicals in bodily fluids.
• Immunology: studies the immune system's response to disease.
• Microbiology: studies microorganisms.
• Genetics: studies genes and their role in disease.
• Surgical pathology: studies tissue samples from surgical procedures.
• Cellular pathology: studies cellular changes at a microscopic level.
• General pathology: examines common changes in various tissues, like inflammation, cancer, ageing, edema, and hemorrhage.
• Systemic pathology: analyzes mechanisms of disease in specific organ systems (e.g., CVS, CNS, GIT).

Types of Pathology Studies

• Human pathology: studies disease in humans using autopsy, biopsy, and cytology (smears, fine-needle aspiration) procedures.
• Experimental pathology: studies disease using animal models and tissue or cell cultures.

Sub-categories for Human Pathology

• Autopsy: Examination of a deceased body by systematically dissecting to see cause of death
• Biopsy: Examination of tissue samples from a living person
• Cytology: Examination of cells obtained from various sources.

Forensic Pathology

• A branch of medicine focused on applying medical knowledge to criminal or civil legal cases, for instance in suspicious death investigations.
• Also referred to as Forensic medicine.

Disease Study

• A disease is a structure or function disorder in humans, animals, or plants.
• Diseases can arise from genetic disorders, environmental factors or injuries.
  • Diseases often show specific symptoms and affect particular locations.
  • Diseases are not simply the result of physical injuries.
• Important factors to consider in disease study include:
  • Definition
  • Epidemiology (where and when it occurs)
  • Etiology (cause)
  • Pathogenesis (how it develops)
  • Morphology (structural changes)
  • Functional consequences
  • Management
  • Prognosis
  • Prevention
  • Categorization (developmental or acquired) followed by sub-categories (inflammatory, neoplastic, genetic, infectious, etc.).

Etiology

• Etiology is the study of the causes of disease and the agent or factor that causes the disease.
• Types of causes include:
  • Etiologic agent: The triggering factor (like bacteria, viruses).
  • Predisposing cause: Factors creating greater susceptibility (smoking).
  • Exciting cause: Factors directly responsible for the disease (hypoxia).

Pathogenesis

• Examines the molecular, physiological, and cellular mechanisms after initial injury, leading to the development of a disease.
• Understanding pathogenesis helps in choosing appropriate therapies .

Cell Responses to Injury

• Cells can adapt, suffer reversible injury, or undergo irreversible injury and die in response to injurious agents.

Clinical Symptoms and Signs

• Symptoms are the patient's complaints (pain, headache).
• Signs are observable characteristics (organomegaly).

Morphology

• Morphology studies the structural changes in diseased tissues.
• Types of morphology assessment include gross appearance (size, shape, weight, color, consistency, surface) and microscopic examination (using stains, like hematoxylin and eosin (H&E) to examine tissues or specific reactions such as immunohistochemistry, or using more advanced technologies like electron microscopy (EM) and scanning electron microscopy (SEM)).

Molecular Pathology

• Examines the molecular level details involved in disease processes, often for cancer diagnostics.
• Example applications include microscopic examinations and techniques such as Polymerase chain reaction (PCR) and DNA sequencing.

Other techniques

• Flow Cytometry (FCM): Analyzes cell properties, especially useful in neoplastic diagnoses
• Image analysis: Measures specific morphological details using images (measurements, shapes, and sizes).

Prognosis

• Prognosis is assessing the expected outcome of the disease and, therefore clinicians also asses the severity.