Expansion
Labile, stable and permanent cell populations
Expansion
- Labile: continuously dividing, with a stem cell population. Surface epithelia (skin, gut, urothelium), bone marrow. Regenerate completely, but are the most vulnerable to chemotherapy and radiotherapy, which explains mucositis, marrow suppression and alopecia
- Stable (quiescent): normally in G0 but able to re-enter the cycle when stimulated. Liver, kidney tubule, pancreas, fibroblasts, smooth muscle, endothelium. The liver’s capacity is remarkable, regenerating after partial hepatectomy
- Permanent: cannot divide. Neurones, cardiac muscle, skeletal muscle. Heal by scarring only
This classification explains the outcome of injury in each organ. Myocardial infarction leaves a collagenous scar rather than new muscle; cerebral infarction leaves a glial scar and a cyst; whereas hepatitis can resolve with complete architectural restoration provided the reticulin framework survives.
Skeletal muscle is a partial exception: satellite cells provide a limited regenerative capacity, sufficient for minor injury but not for major loss.
The framework matters as much as the cells: if the basement membrane or reticulin scaffold is destroyed, even a labile or stable tissue heals by fibrosis rather than regeneration.