Practice question

Physiological stem roles encompass tissue regeneration after injury via symmetric expansion and mobilization, differentiation into specialized cells replenishing turnover, secretion of trophic factors modulating inflammation, angiogenesis and niche, and maintaining homeostatic equilibrium between loss and production. Apoptosis constitutes programmed death mediated by caspase cascade eliminating damaged or unwanted cells, opposite of stem survival function. Stem cells evade apoptosis through Bcl2 and niche PI3K-Akt signals; apoptosis eliminates not generates derivatives. Therefore apoptosis is not stem function but death mechanism controlling cell numbers and tissue sculpting during development.