Bone Development and Growth

Osteogenesis is a complex process of bone formation involving several phases and utilizes various cell, metabolites, hormones, and organic and inorganics components. Numerous genetic factors mediate bone formation. Initially, progenitor cells produce osteoblastic lines, which pass through three major cell differentiation stages: proliferation, maturation of matrix, and mineralization. Based on embryonic origin, ossification is of two types: intramembranous and endochondral. In intramembranous ossification, mesenchymal cells in ossification center directly differentiate into osteoblasts, without prior cartilage formation. It involves mesenchymal cell proliferation in highly vascularized areas of embryonic connective tissue, leading to primary ossification center formation. These cells then synthesize bone matrix at periphery, with continuous differentiation into osteoblasts. The resulting bone undergoes reshaping and is eventually replaced by mature lamellar bone. Sufficient blood supply and communication among cells by lacunar-canalicular system are crucial for bone synthesis and maintenance. In contrast, endochondral ossification begins with the formation of primary ossification center within cartilage. Chondrocytes undergo proliferation, expanding the cartilage through cartilage matrix deposition. Central region of cartilage sees the maturation of chondrocytes into hypertrophic chondrocytes. As primary ossification center forms, marrow cavity expands toward epiphysis. The process is completed by subsequent stages of endochondral ossification in various zones of ossification.