Cellular adaptations (atrophy, hypertrophy)

Cellular adaptations (atrophy, hypertrophy)

Cellular adaptations (atrophy, hypertrophy)

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Cellular Adaptations - The Cell's Survival Kit

Cells adapt to stress to achieve a new steady state, avoiding injury. This involves changes in size, number, or phenotype.

  • Hypertrophy: Increase in cell size → increased organ size.

    • Mechanism: ↑ synthesis of structural proteins & organelles.
    • Physiologic: Uterine growth in pregnancy; skeletal muscle with exercise.
    • Pathologic: Cardiac hypertrophy from chronic hypertension.
  • Atrophy: Decrease in cell size → decreased organ size.

    • Mechanism: ↓ protein synthesis & ↑ protein degradation via ubiquitin-proteasome pathway; autophagy.
    • Causes: Disuse, denervation, ↓ blood supply, poor nutrition, loss of endocrine stimulation.

Histopathology of Hypertrophic Cardiomyopathy

⭐ In cardiac hypertrophy, heart muscle cells enlarge, but this adaptation can progress to contractile dysfunction and heart failure.

Atrophy - Shrink to Survive

  • Definition: A reversible adaptation involving a ↓ in cell size and/or number, leading to reduced organ size or function. It's a retreat to a smaller size to conserve energy and survive.
  • Mechanisms: Primarily driven by ↓ protein synthesis and ↑ protein degradation.
    • Ubiquitin-Proteasome Pathway: Key for degrading cytosolic and nuclear proteins.
    • Autophagy: "Self-eating" where the cell digests its own components via lysosomes, often leaving behind residual bodies (lipofuscin granules).
  • Common Causes:
    • ↓ Workload (disuse atrophy)
    • ↓ Innervation (denervation atrophy)
    • ↓ Blood Supply (ischemia)
    • ↓ Nutrition (marasmus, cachexia)
    • ↓ Endocrine Stimulation (e.g., post-menopausal endometrium)
    • Aging (senile atrophy)

High-Yield: In atrophic cells, accumulations of brownish lipofuscin granules represent indigestible lipid residues from autophagolysosomes, a key sign of free radical-induced lipid peroxidation and cellular aging.

Sarcopenia vs. Normal Muscle

Hypertrophy - Bulking Up Under Stress

  • Definition: ↑ in cell size, leading to ↑ organ size. Occurs in non-dividing cells (e.g., myocytes, neurons). No new cells, just bigger ones.

  • Triggers & Pathways:

    • Mechanical stretch (e.g., chronic pressure/volume load).
    • Trophic signals (e.g., hormones, growth factors).
    • Activates signal transduction (PI3K/Akt, GPCRs) → transcription factors (GATA4, NFAT) → ↑ synthesis of structural proteins.
  • Types & Examples:

    • Physiologic: Uterine smooth muscle in pregnancy; skeletal muscle with exercise.
    • Pathologic: Cardiac hypertrophy from hypertension or aortic stenosis.

Left ventricular hypertrophy vs. normal heart

⭐ In cardiac hypertrophy, there's a switch to fetal/neonatal forms of contractile proteins (e.g., β-myosin heavy chain). This provides slower, more energy-efficient contraction but at the cost of reduced contractile performance, predisposing to heart failure.

High‑Yield Points - ⚡ Biggest Takeaways

  • Atrophy is a decrease in cell size and number, commonly from ↓ workload, denervation, or ischemia.
  • The primary mechanism for atrophy is the ubiquitin-proteasome pathway.
  • Hypertrophy is an increase in cell size, occurring in non-dividing cells like cardiac and skeletal muscle.
  • It is triggered by ↑ functional demand or specific hormonal stimulation.
  • Pathologic cardiac hypertrophy is a major risk factor for sudden cardiac death.

Practice Questions: Cellular adaptations (atrophy, hypertrophy)

Test your understanding with these related questions

A 45-year-old man presents with a hereditary condition affecting iron metabolism. The condition is caused by mutations in a gene that normally stimulates hepatic production of hepcidin, a hormone that downregulates iron absorption by inhibiting ferroportin (an iron transporter) on enterocytes. Due to this genetic defect, the patient has developed iron overload. He presents with skin hyperpigmentation, fatigue, joint pain, and diabetes mellitus. Laboratory studies show elevated serum ferritin and transferrin saturation. The patient is also developing early signs of cardiovascular complications from iron deposition. What would be the first cardiac manifestation in this patient?

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Flashcards: Cellular adaptations (atrophy, hypertrophy)

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Which cellular change is characterized by a decrease in tissue mass due to decrease in size or number of cells? _____

TAP TO REVEAL ANSWER

Which cellular change is characterized by a decrease in tissue mass due to decrease in size or number of cells? _____

Atrophy

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