Introduction to Pathology

Introduction to Pathology

• Pathology is a branch of science that studies the structural and functional changes occurring in cells, tissues, and organs that result in disease.
• The word pathology is derived from Greek words "pathos" meaning suffering and "logos" meaning study.

Branches of Pathology

• Anatomical surgical pathology: Focuses on structural abnormalities in cells and tissues, often through autopsy and biopsy.
• Clinical pathology: Includes various sub-branches analyzing various aspects of disease:

  Hematology:

  • Studies blood diseases and the impact of other diseases on blood.

  Chemical pathology:

  • Examines biochemical abnormalities related to diseases.

  Immunology:

  • Investigates primary immune system diseases and the effects of other diseases on the immune system.

  Microbiology:

  • Studies infectious diseases and their causes.

  Genetics :

  • Analyzes genetic disorders and their impact on health.

General vs. Systemic Pathology

• General pathology: Focuses on the mechanisms of common disease processes, such as inflammation, degeneration, and tumor formation.
• Systemic pathology: Examines the effects of specific diseases on specialized organs.

Disease Definition and Characteristics

• Disease is a clinical manifestation of an underlying abnormality, resulting in signs and symptoms.
• This abnormality can be structural, functional, or both.

Disease Characteristics:

• Etiology: The cause of the disease, whether congenital or acquired.
• Pathogenesis: The mechanism or series of steps involved in the disease process.
• Manifestations: Morphological and functional changes associated with the disease.
• Complications: Secondary effects of a particular disease.
• Prognosis: The expected outcome of the disease, ranging from good to bad.
• Epidemiology: The incidence and distribution of a disease in a population.

Homeostasis

• Refers to the normal steady state of a cell where it functions appropriately and meets physiological demands.

Cell Adaptation

• A new, altered steady state where cells preserve viability by modifying their morphology and function in response to stress or stimuli.

Types of Adaptive Responses:

Cell Atrophy:

• Shrinkage of a cell due to loss of cell substance.
• When a significant number of cells undergo atrophy, the entire tissue or organ diminishes in size.

Causes of Cell Atrophy:

• Immobilization: Due to factors like a fracture.
• Loss of innervation: Examples include poliomyelitis.
• Diminished blood supply: Such as ischemia.
• Inadequate nutrition: Starvation.
• Loss of endocrine stimuli: Like the uterus after menopause.
• Aging: For example, brain atrophy.

Mechanism of Atrophy:

• Reduction of cellular components through:
  • Decreased synthesis.
  • Increased catabolism.
  • A combination of both.

Cell Hypertrophy:

• An increase in the size of cells, leading to an increase in organ size.
• This growth is driven by increased synthesis of structural proteins and organelles.

Types of Hypertrophy:

• Physiological hypertrophy: A normal physiological response, like increased muscle mass in weightlifters due to workload.
• Pathological hypertrophy: An abnormal response like left ventricular hypertrophy in patients with hypertension or heart valve stenosis.
  • In hypertension, the heart muscle faces increased resistance pumping blood.
  • In cases of myocardial infarction, the enlargement of viable cardiac muscle compensates for the loss of neighboring cells due to ischemia.

Mechanism of Cell Hypertrophy:

• Activation of cell receptors, genes, and growth factors that trigger increased protein synthesis and organelle production.

Cell Hyperplasia:

• An increase in the number of cells.

Types of Hyperplasia:

• Physiological hyperplasia:

  • Hormonal: Like the proliferation of breast lobules during lactation.
  • Compensatory: When part of a tissue is removed or diseased, neighboring cells proliferate to compensate.
    • Examples include liver partial resection and connective tissue cell proliferation during wound healing.

• Pathological hyperplasia: Primarily caused by excess hormone or growth factor stimulation.

  • Endometrial hyperplasia: Due to progesterone-estrogen imbalance, leading to abnormal uterine bleeding.
  • Benign prostatic hyperplasia (BPH): Occurs in elderly males, leading to urine retention.

Mechanism of Cell Hyperplasia:

• Growth factor-driven proliferation of mature cells and, in some cases, increased production of new cells from tissue stem cells.

Cell Metaplasia:

• A reversible change where one epithelial or mesenchymal cell type is replaced by another adult cell type.
• This is an adaptive response to stress, where cells sensitive to stress are replaced by a more resistant type.