Cellular Response to Stress, Injury, Aging
Learning Objectives
1. Define cellular adaptation and its purpose.
- Cellular adaptation is a reversible, structural, or functional cellular response to physiologic or
pathologic stressors. It is compensatory in nature, with a goal to achieve an altered steady state
(homeostasis).
2. Define and give examples of 5 types of cellular adaptation.
1. Atrophy – Decrease in cell size and functional capacity due to disuse, denervation, decreased nutrition,
or reduced blood flow.
Physiologic examples: Aging, menopause
Pathologic examples: Brain atrophy, kidney atrophy
2. Hypertrophy – Increase in cell size and functional capacity, often due to increased workload.
Reversible if the stimulus is removed.
Example: Enlarged heart from high blood pressure
3. Hyperplasia – Organized increase in cell number, controlled by proliferation, programmed cell death,
and hormonal or growth factor signals. Can be physiologic or pathologic.
Physiologic examples: Pregnancy (uterine lining), tissue regeneration
Pathologic examples: Skin warts, calluses from excessive stimulation
4. Metaplasia – Reversible replacement of one mature cell type with another, usually due to chronic
irritation or inflammation. Stem cells are reprogrammed to survive stress. Always pathologic but not
always cancerous.
Example: Columnar epithelium replaced by squamous epithelium in smoker’s lungs,cervix
5. Dysplasia – Disorganized cell growth with variation in size, shape, and appearance. Often follows
prolonged metaplasia and may precede cancer. Usually reversible and due to chronic irritation or
inflammation.
Example: Cervical dysplasia detected on a Pap smear
3. Define intracellular accumulations and give examples.
Intracellular accumulations are the buildup of substances within cells that
are either normal cellular components in excess, abnormal
substances, or foreign materials that the cell cannot immediately
degrade or remove. These accumulations can result from metabolic
disturbances, defects in protein folding, enzyme deficiencies, or
exposure to harmful substances.
Examples:
1. Lipids – Fatty substances accumulating in liver cells (e.g., fatty liver/steatosis).
2. Proteins – Abnormal or excess proteins inside cells, like in Alzheimer’s disease (tau
protein aggregates).
