Growth of Cartilage and Bone Tissue

Cartilage is a pliable, avascular connective tissue. Hyaline cartilage is a type of cartilage that protects the ends of long bones and enables smooth joint movements. It also forms the fetal skeleton which will be converted into bone tissue by endochondral ossification.

Cartilage formation begins when either mesenchymal stem cells or fibroblasts differentiate into chondrocytes, specialized cells that divide and secrete a thick gel-like matrix.  

In hyaline cartilage, the chondrocytes stop dividing once they increase in volume 5-12 fold and form the general shape of a bone, known as a cartilaginous model. As the cells undergo apoptosis, blood vessels enter the degenerating cartilaginous model, bringing in osteoblasts, cells that form the new bone tissue.

Osteoblasts synthesize an organic matrix called osteoid, consisting mainly of collagen. Osteoblasts deposit increasing layers of osteoid in a process known as apposition. The osteoid turns into calcified bone due to calcium phosphate crystals in the bone matrix.

Some osteoblasts remain buried in the calcified bone matrix and transform into osteocytes. These cells play major roles in bone and mineral homeostasis and bone remodeling.