Bone Development and Growth
There are two types of bone based on the way the bones form
1. INTRAMEMBRANOUS BONES: broad, flat bones of the skull. These bones form from membrane-like sheets of connective tissue
2. ENCHONDRAL BONES : all other bones.
- Bones first form as hyaline cartilage. The cartilage then gradually changes into bone tissue – a process called OSSIFICATION, which begins near the middle of the diaphysis in an area called the PRIMARY OSSIFICATION CENTER. Later the bone begins to ossify in the epiphysis – these areas are called the SECONDARY OSSIFICATION CENTERS.
- As long as growth is occurring, a “band” of cartilage (called an epiphyseal disk, growth plate) remains between the diaphysis and the epiphysis.
- Bones increase in length as these cartilage cells continue to reproduce and ossify
- Cartilage cells form cells called OSTEOBLASTS. These cells produce bone matrix and once the cell is enclosed in bone matrix it is considered to be a mature bone cell and called an OSTEOCYTE
- Growth in thickness of bone occurs as osteoblasts from beneath the periosteum produce bone matrix and built compact bone just underneath the periosteum
- Bone tissue is constantly being replaced as special cells called OSTEOCLASTS dissolve bone tissue from within the medullary cavity – a process called RESORPTION. At the same time new bone tissue is being added to the outside of the bone.