Bone

Abstract

Bone is a hard tissue that; protects the body organs, produce blood cells, and stores minerals. In a new-born body there is more than quantity of 270 bones and during different life stages this number decreases to 206 by coalisions in mature skeleton. Bone tissue is basically divided into three types as long, short and flat according to its shape. Long and short bones are derived by cartilage model as endochondral ossification, flat bones are formed by concentration of mesenchymal tissues (intramembranous ossification). The hard outer portion that contains lower amount of space is called cortex and more soft and spongy structure that is biologically more active is the inner part and called trabecular bone. Bone tissue as the basis contains three type of cells that are; osteoblasts, osteoclasts and osteosits. Osteosits are the main types (larger amount) of cells in the mature skeleton that consist of trapped former osteoblast in the newly formed matrix. Osteoblasts are cells that are responsible for bone production while osteoclast are bone destructor. Bone matrix is developed by organic and inorganic component. Organic matrix is 40 % of dry weight of bone tissue and 90 % of this type of matrix is formed by collagens (mainly type 1). 60 % of the dry weight of the bone is inorganic matrix that contains calcium hydroxyapatite and calcium phosphate. Bone’s hard and mineralized nature is closely associated with the dynamic and self-renewal behavior. This dynamic structure; ensures the continuum of structural integrity, mechanical resistance and contributes to heal without scar tissue. This is achieved through the construction and destruction of the bone regularly. When the balance of construction and destruction of bone fails, diseases such as osteoporosis, osteopetrozis can be seen. Cortical and trabecular bone remodels by osteoblastic and osteoclastic activities throughout life. All bone tissue can completely refresh itself in 4 - 20 years.