Gangrene: Types and Pathogenesis

Study Notes

Gangrene

Definition: Necrosis of large tissue with putrefaction, characterized by a black, foul-smelling appearance.
Pathogenesis: Putrefactive organisms infect necrotic tissue. Hemoglobin (released from hemolyzed red blood cells) combines with hydrogen sulfide (produced by bacteria) to form iron sulfide, giving the tissue a dark coloration.

Types of Gangrene

Dry gangrene:
- Affects the surface of the skin, primarily limbs, especially toes.
- Caused by arterial obstruction.
- Commonly occurs in individuals with impaired peripheral blood flow like diabetics.
- Characterized by dry, shrunken, and dark reddish-black tissue resembling mummified flesh.
Wet gangrene:
- Commonly affects the small intestine, appendix, lung, uterus, and limbs.
- Caused by both arterial and venous obstruction.
- Saprophytic microorganisms like Clostridium perfringens or Bacillus fusiformis infect the tissue.
- Characterized by wet, swollen, foul-smelling, black, or green tissue.
- Systemic manifestations: Toxic products from bacteria absorption lead to septicemia and potentially death.
Gas gangrene:
- Affects deep contaminated wounds with considerable muscle damage.
- Caused by gas-forming bacteria.
- Characterized by swollen tissue and gas bubble formation.
- The infection spreads rapidly and causes severe toxemia.
- Less common in civilian practice but a serious complication of war wounds.

Cellular Adaptations to Stress

Adaptability of cells: Cells adapt to altered environments through physiological and pathological stimuli.
Changes in growth pattern: This includes hypertrophy, hyperplasia, atrophy, and metaplasia.

Significance of Cellular Adaptations

These adaptations are common responses in diseases.
Certain adaptations in growth can create a fertile ground for the later development of neoplasia (cancer formation).
This terminology is used in clinical work.

Cellular Adaptations to Stress: Changes in Growth Pattern

Hypertrophy:
- Definition: Abnormal increase in the size and weight of an organ or tissue due to increased cell size.
- Cause: Increased functional demand.
- Types: Physiological hypertrophy (e.g., pregnant uterus, muscular exercise) and pathological hypertrophy (compensatory or adaptive).
- Physiological Hypertrophy: Skeletal muscle hypertrophy in response to exercise.
- Pathological Hypertrophy:
  - Compensatory: Occurs in paired organs (e.g., kidney) when one is destroyed or removed, the other enlarges to compensate.
  - Adaptive: Occurs in muscular hollow organs (e.g., heart, stomach, bladder, intestine) in response to chronic partial obstruction, requiring increased muscle contraction.
Hyperplasia:
- Definition: Increase in the size and weight of an organ or tissue due to increased cell number.
- Types: Physiological hyperplasia (e.g., breast and genital organs at puberty) and pathological hyperplasia.
- Causes of Pathological Hyperplasia: Compensatory (e.g., bone marrow after hemorrhage), hormonal (e.g., endometrium and mammary gland due to estrogen), irritation (mechanical, bacterial, toxic), deficiencies (e.g., iodine deficiency causing thyroid hyperplasia), and viral (e.g., pox virus causing epithelial hyperplasia).
Atrophy:
- Definition: Decrease in tissue size after reaching full growth, due to decreased cell number or size.
- Types: Physiological atrophy (e.g., thymus atrophy) and pathological atrophy.
- Physiological Atrophy: Atrophy of the thymus.
- Pathological Atrophy:
  - General Atrophy: Malnutrition and starvation atrophy, senile atrophy.
  - Localized Atrophy:
    - Disuse atrophy
    - Pressure atrophy
    - Vascular atrophy
    - Neuropathic atrophy
    - Endocrine atrophy