The growth plate: Zonal architecture, plasticity, and endocrine control of linear growth

The growth plate (physis) is a highly specialized cartilaginous organ that drives longitudinal bone growth and ultimately determines adult stature. Its zonal architecture, including the resting, proliferative, hypertrophic, and calcification zones, integrates stem-like progenitor activity, clonal chondrocyte expansion, matrix remodeling, vascular invasion, and replacement by bone. Here, we review how the structural organization of the growth plate emerges from the interplay among extracellular matrix composition, sulfation pathways, and canonical paracrine signaling pathways, including Ihh-PTHrP, BMP, Wnt, and FGF. We highlight advances in our understanding of chondrocyte fate, including lineage-tracing studies demonstrating that resting-zone PTHrP⁺ cells function as skeletal stem cells and that hypertrophic chondrocytes can transdifferentiate into osteoblasts or dedifferentiate into progenitors rather than undergoing obligatory apoptosis. We also summarize how endocrine axes, including the GH/IGF-1, thyroid hormone, sex steroids, glucocorticoids, and vitamin D, coordinate the tempo of growth, the dynamics of growth plate senescence, and the timing of epiphyseal fusion, with emphasis on species differences between rodents and humans. Finally, we use monogenic skeletal dysplasias, endocrine disorders, and acquired conditions such as rickets and slipped capital femoral epiphysis as "experiments of nature" that illuminate how specific molecular perturbations disrupt growth plate physiology. Together, these converging lines of evidence reframe the growth plate as a dynamic stem-cell and progenitor niche whose fate is plastic, highly regulated, and increasingly targetable for therapy in disorders of linear growth.