VAN 211: Veterinary Histology and Embryology (2+2)

Bone (osseous tissue)

BONE

Bone or osseous tissue consists of cells, collagenous fibres, and an intercellular matrix of organic substances.

• The organic matrix is chiefly made up of osseo mucoid and in this matrix, collagen fibres are embedded and the fibrils form a major portion of the intercellular substance.
• The inorganic matter is composed of calcium phosphate, calcium carbonate and small amount of other minerals. The minerals are present in the form of crystals of hydroxyaptite embedded in the matrix and are arranged in a regular manner in relation to the collagen fibres.
• The bone cells or osteocytes are irregularly oval cells with fine cytoplasmic processes, a large oval nucleus and faintly basophilic cytoplasm. These cells occupy spaces called lacunae in the solid intercellular substance and numerous canaliculi radiate from the lacunae and are occupied by the cytoplasmic processes of osteocytes.
• The intercellular substances of bone are in the form of thin plates or lamellae between or within which are the lacunae and canaliculi occupied by osteocytes and their processes. The arrangement of these lamellae is different in compact and cancellated bones.
• Organisation of bone tissue:
  • Grossly two types of bone may be distinguished the spongy or cancellous and the dense or compact.
  • The spongy and compact varieties do not represent histologically distinct types of osseous tissues, but differ only in the degree of porosity. In the spongy bone, the space is large and the bony matter reduced to a network of slender bars of bone.
  • In compact bone, the bony tissue is abundant and more densely packed. The histological character of the cells and intercellular substance are the same in both.
• In all bones, there is an outer layer of compact bone enclosing the cancellated bone and within the cancellated bone is the bulk of the bone, except in the diaphysis of long bones and certain flat bones of the skull.