Development and growth of bones
Last reviewed: 23.04.2024
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The skeleton of the fetus undergoes connective tissue (membranous) and cartilaginous stages in its development. There are two groups of bones that differ in their origin. Some bones are formed directly on the basis of connective tissue, bypassing the cartilage stage. Bones formed in this way (membranous osteogenesis) are the bones of the cranial vault. Other bones are both membranous and cartilaginous. On the basis of the cartilaginous model, bones of the trunk, limbs, and the base of the skull are formed. Isolate endochondral (intracardial), perichondral and periosteal methods of bone formation. If ossification occurs in the thickness of the cartilage, it is called the endochondral osteogenesis. In the thickness of the cartilage there are one or more points of ossification. Near the sprouting of connective tissue fibers and blood vessels in the cartilage, young bone cells (osteoblasts) form bony beams, which increase in size, grow in different directions. Osteoblasts are transformed into mature bone cells - osteocytes, eventually forming a bone. If the bone substance is formed along the periphery of the cartilage (with the participation of the perichondrium), this is perichondral osteogenesis. The formation of bone due to the osteogenic function of the periosteum is called periosteal osteogenesis.
Depending on the timing of appearance in the cartilage models of bone tissue, the primary (primary) and secondary (secondary) ossification centers are distinguished. The primary centers of ossification are laid in the diaphysis of the tubular bones, in many spongy and mixed bones in the first half of the intrauterine period. Secondary centers of ossification are formed in the epiphyses of tubular bones at the very end of fetal life and mainly after birth (up to 17-18 years). Due to the additional centers of ossification, the bones form sprouts, knolls and ridges.
After the formation of centers of ossification in the diaphysis, and then in the epiphysis, a layer of cartilage (epiphyseal cartilage) is preserved between them. Due to this cartilage the bone grows in length. Epiphyseal cartilage is replaced by bone tissue to 13-20 years. The growth of bone in thickness is due to the activity of the inner layer of the periosteum and endosteum.
The bony canal of tubular bones arises inside the diaphysis during the resorption of the endochondrial bone.
The growth and aging of bones depends on many factors: for example, the state of the organism itself (lifestyle) and the influence of the external environment.
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