Explore the various ways in which cells adapt to different types of stressors, including hypertrophy, hyperplasia, atrophy, and metaplasia.
Cellular Adaptations in Response to Stress
Study guide – concise, organized, and ready for review
| Adaptation | Definition | Typical Triggers | Key Molecular Players | Outcome |
|---|---|---|---|---|
| Atrophy | Reduction in cell size, organ mass, and functional capacity | Disuse, denervation, decreased workload, loss of endocrine stimulation, aging | ↓ protein synthesis, ↑ protein degradation (ubiquitin‑proteasome, autophagy) | Conserves energy; reversible if stimulus removed |
| Hypertrophy | Increase in cell size (often with enhanced functional output) | Increased workload (e.g., muscle exercise, cardiac pressure overload), hormonal stimulation (e.g., estrogen) | ↑ protein synthesis (mTOR, Akt), sarcomere addition (cardiac), ribosome biogenesis | Improves contractile force; may become maladaptive (e.g., heart failure) |
| Hyperplasia | Rise in cell number via proliferation | Hormonal stimulation (estrogen → endometrium), compensatory growth after loss (liver regeneration), chronic irritation (skin) | Growth factors (EGF, PDGF), cyclins/CDKs, MAPK/ERK pathway | Restores tissue mass; can be physiological or pathological (e.g., neoplasia) |
| Metaplasia | Reversible replacement of one differentiated cell type by another better suited to the new environment | Chronic irritation, inflammation, hormonal changes (e.g., smoking → bronchial epithelium) | Transcription factors (SOX2, p63), stem/progenitor cell activation, BMP/Wnt signaling | Protective short‑term; risk of dysplasia/carcinoma if stimulus persists |
| Dysplasia | Disordered growth with loss of normal orientation and maturation | Persistent irritants, carcinogens, chronic inflammation | Mutations in tumor‑suppressor genes (p53), altered cell‑cycle control, epigenetic changes | Premalignant lesion; may revert or progress to carcinoma |
| Anaplasia | Loss of differentiation; cells become primitive and pleomorphic | Advanced malignancy | Oncogene activation, loss of differentiation markers, genomic instability | Indicator of high‑grade cancer; irreversible |
| Pathway | Primary Stimuli | Main Effectors | Adaptive Result |
|---|---|---|---|
| PI3K/Akt/mTOR | Growth factors, nutrients | Akt, mTORC1, S6K | Promotes hypertrophy & hyperplasia (protein synthesis, cell growth) |
| AMPK | Low ATP/energy stress | AMPKα, TSC2 | Inhibits mTOR, stimulates autophagy → protects against energy depletion |
| **MAPK/ERK |