Nail courses – Bone tissue
It belongs to stromal tissues (just like connective and cartilage tissue), constitutes the skeleton of the body having a connective and gap-filling role, it is composed of cellular space and the so-called intercellular matrix and it is rich in blood vessels (except for cartilage tissue). Bone tissue is the hardest and most weight-bearing tissue of the body. It is solid and elastic at the same time.
The structure of bone tissue:
- organic matrix (collagen fibers or in other words: collagenous protein constituents of skeleton which ensure the elasticity of bones),
- inorganic matrix (mineral salts providing the hardness and solidity of bones).
Bone tissue is composed of:
1. Cellular matrix, bone cells
- Osteocytes: large, plum stone –shaped cells with extensions which produce substances needed for the intercellular matrix (e.g. collagen).
- Osteoblasts: are situated at the growing point of bones (under the cartilaginous ends and under the periosteum), or at the place of their reconstruction (e.g. bone fracture).
- Osteoclasts: are found in the hollow part of bones and where bone absorption takes place.
2. Intercellular matrix
- organic matters that are composed of protein, or of so called collagen fibers (like ferro-concrete, the elasticity and tensile-strength of which is provided by steel wire) which constitute about 35% of the bone.
- inter-fibre spacing that consists of mineral salts (like the hard material of ferro-concrete) which constitutes about 65% of the bone.
Bones consist of two parts with different structures:
1. Compact Bone:
compact and thick bone matrix forming the outer layer of bones,
it is homogeneous to the naked eye, having regular structure under microscope
it is thin in most bones,
the cylinder-like part in the middle of the so called cylindrical bones (e.g. thighbone) consists of almost only this kind of bone,
its thickness is affected by loading (the thighbone is thick) and its function.
2. Spongy Bone:
- found in the internal part of bones,
- forms e.g. the thicker bone ends jointed by symphysis, cube- shaped and flat bones,
- irregular lattice of thin, fine flakes and beams containing bone tissue, the spaces of which are filled with bone marrow,
- they are formed in a regular system, the order and type of which corresponds to the static lines of forces resulting from the weight placed on bones,
- more massive
- the trabeculae of bones is capable of rebuilding itself when loading is changed (e.g. one of the limbs is shortened).
Under a microscope bone tissue is constituted in a regular structure, in a system of laminaes which are a so-called basic trabeculae of bones. These are canals running parallel with the bone’s longitudinal axis and there are lamellas around them forming concentric circles (as if we would insert them into each other with tubes). Real bone tissues are found within the spaces among tubes while the tubes provide the intercellular matrix. Blood vessels which transfer nutritives run in the innermost part of the tube. The bone is constantly changing, the osteoclasts breaking it up, while osteoblasts build it.
Growth of bones occurs:
- in longitudinal direction (cartilage lamina)
- in their thickness (deposition from periousteum).