BONES:basic information.

What is a bone?

• It is an osseous tissue (also called bone tissue)that later turns into bone.
• It is a type of dense connective tissue with great strength and resilience.
• It consists of cells,fibres and a matrix.
• Matrix is extra cellular and has a calcium deposition in it.
• The calcium salts forms 2/3rd of the bone and the remaining part forms 1/3rd of the connective tissue.
• The calcification provide strength to the bone tissue.
• The presence of fibre gives some amount of elasticity to the tissue.

What are the functions of the bone?

• Bone gives shape and support to the body and resist any form of stress.
• They provide surface for the attachment of muscle ,tendonand ligamens.
• They serve as lever for muscle action.
• The skull, vertebral column and thoracic cage protect brain, spinal cord,thorax and some abdominal viscera.
• Bone marrow inside the bones manufacturers blood cells.
• Bones store about 97% of body calcium and phosphorus.
• Bone marrow contains reticuloendothelial cells which are phagocytic in nature and take part in immune response of the body.
• The larger paranasal air sinuses example ethmoidal sinuses affect the timber of the voice.

Architecture of bones

• All bones have an outer layer of compact bone and the interior covered by cancellous bone.

Compact bone

• They are hard and forms the outer layer of bone.
• It consists of longitudinal running canal called harvesian canal.
• Harvesian canal surrounded by lamellae to form osteon or harvesian system.

Cancellous bone

• Meshwork of tiny rods or plates of bone and contain numerous spaces ; appearance resembles that of sponge.
• They are found on the interior of the bone.
• The spongy bone at the bone ends is covered by a thin layer of compact bone.
• Trabeculae are thin and spread out in a meshwork.

• The newly formed bones are usually cancellous bone and later they are converted into compact bone.
• The bone is covered by periosteum.
• The articular surface of the bone is covered by articular cartilage.
• The marrow cavity of the bone and space between the spongy bone are filled by highly vascular tissue called bone marrow.
• At both the ends the marrow is red in colour.
• The yellow marrow is found in the shaft of the bones in the adult.

Parts of a bone

   A young long bone consist of

• Diaphysis 
• Epiphysis
• Epiphyseal cartilage
• Metaphysis

Diaphysis

• It ossified from primary ossification center to form the shaft of the bone.
• Composed of thick compact bone that covers the thin spongy bone which encloses marrow cavity.

Epiphysis

• Part of the bone that ossified from secondary centres.
• It forms the ends of the long bone.

Epiphyseal cartilage

• Plate of cartilage seen between epiphysis and metaphysis of a young growing bone.
• When the bone achieves full length the epiphyseal cartilage replaced by the bone , thus further growth stops.

Metaphysis

• The end of the diaphysis adjuscent to the epiphyseal cartilage .
•  Actively growing area of the long bone.