osteogeneesi

Osteogeneesi, or bone formation, is the process by which new bone tissue is produced. It occurs through two main mechanisms: intramembranous ossification and endochondral ossification. Intramembranous ossification forms flat bones such as the skull and clavicles. In this process mesenchymal cells condense and differentiate directly into osteoblasts, which lay down osteoid that mineralizes into mature bone. Endochondral ossification forms most of the skeleton, especially long bones. A cartilage model forms first; chondrocytes enlarge and calcify, and a primary ossification center develops as osteoprogenitor cells invade and replace cartilage with bone. Later secondary ossification centers appear at the ends of bones.

Osteoblasts produce osteoid, which mineralizes to become bone; osteocytes derive from osteoblasts and reside in lacunae. Bone remodeling is carried out by osteoclasts, which resorb bone, and osteoblasts, which form new bone, maintaining structural integrity throughout life.

Regulation involves signaling pathways such as bone morphogenetic proteins, Wnt/β-catenin, Hedgehog, and Notch, along with hormonal controls including growth hormone and IGF-1, parathyroid hormone, calcitonin, and vitamin D. Mechanical loading also stimulates osteogenesis.

Two major bone tissue types result from these processes: woven bone, produced rapidly during development or repair, and mature lamellar bone, organized into osteons in cortical bone and trabeculae in trabecular bone.

Clinical relevance: impaired osteogenesis can lead to conditions such as osteogenesis imperfecta; osteoporosis reflects imbalanced remodeling with reduced bone mass; fracture healing recapitulates aspects of endochondral ossification. Understanding osteogenesis informs treatments and tissue engineering strategies.