osteogenezë

Osteogenezis is the process by which bone tissue is formed. This complex biological process involves the differentiation of progenitor cells into osteoblasts, which are the bone-building cells. Osteogenesis can occur through two primary mechanisms: intramembranous ossification and endochondral ossification.

Intramembranous ossification is the direct formation of bone from mesenchymal connective tissue. This process is prominent during fetal development for the formation of the flat bones of the skull and the clavicles. Mesenchymal cells condense and differentiate into osteoblasts, which then secrete osteoid, the unmineralized bone matrix. This osteoid gradually mineralizes, trapping osteoblasts within lacunae and forming mature osteocytes.

Endochondral ossification is the formation of bone from a pre-existing cartilage model. This is the primary mechanism for the development of most bones in the body, including the long bones of the limbs. A hyaline cartilage model is first formed, which then undergoes changes. A primary ossification center appears in the diaphysis (shaft) of the bone, where cartilage cells hypertrophy and die, and blood vessels invade. Osteoblasts then deposit bone matrix on the remnants of the calcified cartilage. Secondary ossification centers eventually appear in the epiphyses (ends) of the bone, leading to the formation of spongy bone. The region between the diaphysis and epiphysis, known as the epiphyseal plate, remains as cartilage and is responsible for longitudinal bone growth throughout childhood and adolescence. After growth ceases, the epiphyseal plate ossifies, and the bone stops growing in length.