Chondroblasts secrete cartilage matrix forming bone

uring 8th to 12th week of development.
Chondroblasts secrete cartilage matrix forming bone model. (b) Cartilage calcifies, and a periosteal bone
collar forms around diaphysis. Chondrocytes in the cartilage model produce holes in the matrix and
chondrocytes die. Blood vessels grow toward cartilage. Osteoblasts develop and secrete osteoid around
calcified cartilage shaft and form a layer of osteoid. Periosteal bone collar formed. (c) Periosteal bud
extends into cartilage shaft and the primary ossification center forms in the diaphysis. Most formed by
12 th week of development. Bone development extends in both directions toward epiphyses as bone
replaces degenerating cartilage. (d) Secondary ossification centers form in epiphyses. Not all secondary
ossification centers are formed at birth. Hyaline cartilage calcifies and degenerates in epiphyses. Blood
vessels enter and osteoprogenitor cells enter laying down bone. Osteoclasts resorb some bone matrix
creating the hollow medullary cavity. (e) Bone replaces almost all cartilage, except the articular cartilage
and epiphyseal cartilage. By late bone development, almost all of the hyaline cartilage is displaced by
bone. Hyaline cartilage remains as articular cartilage only on the articular surface of each epiphysis and
at the epiphyseal plates. (f) Lengthwise growth continues until the epiphyseal plates ossify and form
epiphyseal lines. Lengthwise bone growth continues into puberty until the epiphyseal plate is converted
to the epiphyseal line.
7.5 Bone Growth & Remodeling
13. Describe and compare appositional and interstitial bone growth: