Cell Injury: Damage to cells and their environment (extracellular matrix) leads to tissue/organ injury.
Homeostasis: Cells can adapt to physiological demands or stress to maintain a steady state.
Adaptation: Reversible structural or functional response to normal or adverse conditions.
Example: Uterus enlarges during pregnancy.
Adaptation to Stress: Increases size (hypertrophy) or number (hyperplasia) of cells.
Cellular Injury Classification:
Reversible Injury: Sublethal.
Irreversible Injury: Lethal.
Types of injury:
Chemical
Hypoxic (lack of oxygen)
Free radical
Unintentional/intentional
Immunologic/inflammatory.
Cellular injury disrupts structures/deprives oxygen and nutrients.
Pathologic Calcification: Involves calcium accumulation due to cellular death.
Cellular Death: Confirmed by nuclear changes; two main types:
Necrosis: Uncontrolled death due to injury.
Apoptosis: Programmed cell death.
Autophagy: Nutrient deprivation can trigger survival strategies leading to cell death.
Aging leads to structural and functional changes, reducing recovery capacity from injury.
Distinguishing between physiologic and pathologic changes with aging is challenging.
Atrophy: Decrease in cell size.
Can be physiologic (e.g., thymus gland in childhood) or pathologic (e.g., disuse atrophy from immobilization).
Affects skeletal muscle, heart, brain, etc.
Hypertrophy: Increase in cell size due to increased demand or hormonal stimulation.
Types:
Physiologic: E.g., muscle growth from exercise.
Pathologic: E.g., heart enlargement due to hypertension.
Hyperplasia: Increase in cell number from increased cell division, can be compensatory or hormonal.
Example: Liver regeneration post-surgery.
Dysplasia: Abnormal growth not a true adaptation, characterized by disorganized cell architecture.
Not cancer, but reversible if stimulating factors are removed.
Metaplasia: Reversible replacement of one cell type by another, often seen in response to chronic irritation.
Example: Replacement of ciliated cells in smokers by squamous cells.
Understanding cellular adaptations, injuries, and death processes is crucial for disease comprehension and management.