Proliferative Zone - rapidly dividing chondrocytes (basophilic) that organize into distinct columns ("stacks of coins").
Zone of Hypertrophy - chondrocytes (basophilic) cease dividing and grow in size. The cartilage matrix forms (lightly basophilic) linear bands between the columns of hypertrophied cells.
Zone of Calcification - the cartilage matrix becomes calcified inhibiting the diffusion of nutrients. The dying chondrocytes are removed leaving longitudinal spicules of calcified cartilage (intensely basophilic).
Zone of Ossification - osteoprogenitor cells migrate into the cavities with the new blood vessels. New bone (eosinophilic) forms on the scaffold of calcified cartilage (basophilic).
Osteoblasts - condense on the spicules of calcified cartilage and produce new bone (osteoid).
Osteoclasts (#1, #2 and #3) - large, multinucleated cells that remove bone tissue (both mineralized matrix and type I collagen).
(The zone of ossification is easier to see in MH 046 Bone).