Bone growth at the epiphyseal growth plate is endochondral (aka interstitial) is linear.
Bone Growth: Endochondral (Linear)
epiphyseal growth plate
Reserve zone
- Filled with typical fetal hyaline cartilage cells, responsible for growth in length – these cells "lead the growth pack," in essence.
Proliferative zone
- Filled with chrondrocytes that proliferate but do NOT hypertrophy, regulated by Indian hedgehog – this prevents the growth plates from inactivating until puberty when the child reaches full growth the growth plates degenerate to epiphyseal lines.
Hypertrophic zone
- Filled with hypertrophic chondrocytes (we can identify their nuclei and lipid droplets) – they undergo apoptotic enlargement and are the future site of ossification (bony matrix extension).
- They mineralize the surrounding cartilage, attract vasculature via VEGF (vascular endothelial growth factor), and that vasculature then recruits chondroclasts to degrade the carilage and form osteoblasts, which secrete the osteoid (bony matrix).
Vascular Invasion.