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Bone development and growth
Last reviewed: 04.07.2025
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The fetal skeleton goes through connective tissue (membranous) and cartilaginous stages in its development. Two groups of bones can be distinguished, differing in origin. Some bones are formed directly on the basis of connective tissue, bypassing the cartilaginous stage. Bones formed in this way (membranous osteogenesis) are the bones of the cranial vault. Other bones go through both membranous and cartilaginous stages. The bones of the trunk, limbs, and base of the skull are formed on the basis of the cartilaginous model. There are enchondral(intracartilaginous), perichondral, and periosteal methods of bone formation. If ossification occurs in the thickness of the cartilage, it is called enchondral osteogenesis. One or more ossification points arise in the thickness of the cartilage. Near the connective tissue fibers and blood vessels that have grown into the cartilage, young bone cells (osteoblasts) form bone beams that increase in size and grow in different directions. Osteoblasts turn into mature bone cells - osteocytes, and eventually bone is formed. If bone substance is formed along the periphery of the cartilage (with the participation of the perichondrium), this is perichondral osteogenesis. Bone formation due to the osteogenic function of the periosteum is called periosteal osteogenesis.
Depending on the time of appearance of bone tissue in cartilaginous models, primary and additional (secondary) ossification centers are distinguished. Primary ossification centers are laid in the diaphyses of tubular bones, in many spongy and mixed bones in the first half of the intrauterine period. Secondary ossification centers are formed in the epiphyses of tubular bones at the very end of intrauterine life and mainly after birth (up to 17-18 years). Due to additional ossification centers, processes, tubercles and ridges are formed in bones.
After the formation of ossification centers in the diaphyses, and then in the epiphyses, a layer of cartilage (epiphyseal cartilage) remains between them. Due to this cartilage, the bone grows in length. The epiphyseal cartilage is replaced by bone tissue by the age of 13-20. Bone growth in thickness is achieved due to the activity of the inner layer of the periosteum and endosteum.
The medullary canal of tubular bones arises inside the diaphysis during the resorption of endochondral bone.
The growth and aging of bones depend on many factors: for example, the state of the body itself (lifestyle) and the influence of the external environment.
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