MAIN FEATURES AND COMPONENTS OF BONE TISSUE
Bone tissue is a type of connective tissue that has two main components: resident cells originated from the mesenchyme and a mineralized extracellular matrix.
There are in the bone two cell populations that are originated from two different lineages: osteoblastic and osteoclastic. Each has specific distribution and functions within the bone.
The extracellular matrix of the bone is quite unique, as it is composed of an organic portion and a mineralized portion.
These are the main characteristics of the bone extracellular matrix:
– A high amount of type I collagen fibers. Depending on the type and region of the bone the fibers are disorganized or highly organized.
– The presence of many other kinds of molecules in the fundamental extracellular matrix, mainly proteoglycans and glycoproteins, some of which are exclusive or characteristic of bone tissue.
– Sections of bones may sometimes be confused with cartilage sections. However, collagen fibers are acidophilic and stain well with eosin. This means that the bone matrix appears pink after H&E staining, unlike the cartilage matrix, which stains predominantly in blue-blueish with hematoxylin.
– Bone matrix is calcified due to the deposition of hydroxyapatite crystals (formed from calcium phosphate) on the collagen fibrils.
Histological Sections of Bone and Teeth
Due to their rigid consistency, hard tissues require special techniques for obtaining histological sections. See how this is done in the section dealing with Hard Tissue Preparation – pages 1-26 and 1-27.