Question

How does structure and function of skeletal bone contribute to growth and development?

Answer 1

Endochondral ossification leads to the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed by this proces leading to the growth of body frame.

These bones are called endochondral bones. By this process the future bones are first formed are hyaline cartilage models.

The process involves following events :-

During the 3rd month after conception, the perichondrium that surrounds the hyaline cartilage becomes infiltrated with blood vessels &osteoblasts and finally changes into a periosteum.

The osteoblasts form a collar of compact bone around the diaphysis. At the same time, the cartilage in the center of the diaphysis begins to fragment . Osteoblasts penetrates in the disintegrating cartilage and replaces it with spongy bone, leads to the formation of primary ossification centers.

Ossification continues from here to the end of the bones. Afterspongy bone is formed in the diaphysis then osteoclasts break down the newly formed bone to open up the medullary cavity.

The cartilage in the epiphyses continues to grow so the developing bone increases in length. Later after birth,the secondary ossification centers form in the epiphyses. Ossification in the epiphyses is similar to the diaphysis except that the spongy bone is retained instead of being broken down to form a medullary cavity. When secondary ossification is complete, the hyaline cartilage is totally replaced by bone except in two areas ie (a region of hyaline cartilage remains over the surface of the epiphysis as the articular cartilage & another area of cartilage remains between the epiphysis and diaphysis).

This is the epiphyseal plate or growth region.

Bones grow in length at the epiphyseal plate is similar to endochondral ossification. The cartilage in the region of the epiphyseal plate next to the epiphysis continues to grow by mitosis. The chondrocytes, in the region next to the diaphysis gradually age & degenerate. Osteoblasts move in to ossify the matrix to finally form bone. This process continues throughout childhood and the adolescent years until the cartilage growth slows down and finally stops.

When cartilage growth ceases in the early twenties, the epiphyseal plate completely ossifies so then only a thin epiphyseal line remains and the bones can no longer grow in length.

Note: Bone growth is under the influence of growth hormone from the anterior pituitary gland and sex hormones from the ovaries and testes.

Even though bones stop growing in length in early adulthood, they can continue to increase in thickness or diameter throughout life in response to stress from increased muscle activity or to weight. The increase in diameter is called appositional growth. Osteoblasts in the periosteum form compact bone around the external bone surface. At the same time, osteoclasts in the endosteum break down bone on the internal bone surface to control bone growth.