Introduction to Pathology

Introduction to Pathology

• Pathology is the science that studies the nature of disease.
• Pathology is classified into general and systemic pathology.
• General pathology studies the general reactions of cells and tissues to injuries that occur in disease processes.
• Systemic pathology studies specific disease processes or reactions that affect particular organs/organ systems (e.g., cardiovascular system (CVS), central nervous system (CNS), gastrointestinal tract (GIT)).

Applied Classification of Pathology

• Necropsy pathology examines tissues from dead bodies (cadavers) to determine the cause of death.
• This is also called autopsy.
• Surgical pathology examines tissues from living patients to diagnose specific conditions.
• This is called biopsy.

Biopsy Types

• Needle (or core) biopsy: Pathologists or clinicians insert a needle into a mass to collect a tissue sample.
• Incisional biopsy: A surgical cut is made to collect a larger tissue sample.
• Excisional biopsy: The entire mass is removed for diagnosis.

Classification of Pathology by Specimen Type

• Histopathology is the examination of tissues to diagnose conditions.
• Cytopathology is the microscopic study of exfoliated cells within bodily fluids.

Fine Needle Aspiration Cytology (FNAC)

• FNAC uses a thin needle to take a few cells from a mass lesion for cytology.
• This method is often used for superficial masses and deep masses ( with radiology assistance).

The Disease

• The disease is characterized by structural and functional changes in organs and tissues due to exposure to irritants.
• The irritant can be the causative/etiological agent of the disease.

Classification of Diseases

• Hereditary: Diseases resulting from chromosomal abnormalities or gene mutations.
• Acquired: Diseases obtained not genetically, such as:
  • Inflammatory
  • Neoplastic (tumors)
  • Degenerative (e.g., aging)
  • Metabolic

Items of Study for Diseases

• Definition
• Etiology (cause)
• Pathogenesis (mechanism of disease)
• Morphological features (gross and microscopic appearance)
• Complications (resulting from the disease)
• Prognosis (prediction of outcome)

Etiology of Disease

• Predisposing causes: Factors making someone more susceptible to a disease (e.g., heredity, low immunity).
• Exciting causes: Factors directly causing the disease (e.g., infection).

Pathogenesis of Disease

• The mechanisms by which the etiological/disease causing agent instigates the disease process.

Morphology of Disease

• Gross (macroscopic) morphology: Examination of the tissue using the naked eye. This involves noting size, shape, weight, color, consistency, and cut section of the tissue.
• Microscopic morphology: Examination of tissue sections using a light microscope. This is used to determine the nature of the disease.

Complications of Disease

• Complications include additional pathological changes post the normal course of the disease.
• Examples include common cold leading to acute bronchitis, and acute bronchitis leading to pneumonia.

Prognosis of Disease

• Prognosis predicts the expected outcome of the disease.
• Good prognosis suggests likely recovery.
• Poor prognosis suggests permanent disability or death.