Zoology Assignment Help >> Defining Bone, Bone General Features, Types of Bone

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Defining Bone

Bone is a highly mineralized connective tissue. Connective tissue part is 1/3 and mineral part is 2/3. It is mechanically dynamic tissue and acts as a homeostatic reservoir for ions like calcium, magnesium. and phosphorus.

General Bone features

(1) Bone is made up of osteocytes

(2) They lie in lacunae.

(3) Mature osteocyte does not divide.

(4) Each lacunae is interconnected with adjacent lacunae by canaliculi.

(5) Intercellular matrix is made up of (1/3 part) ossein and (213 part) inorganic phosphates called hydroxyapetite.

(6) It is highly vascular.

(7) It has greater regenerative power than any other tissue of the body except blood.

(8) Blood vessels are lodged in a network of slender branching' canals. Haversian canals run parallel to the main axis of the body while Volkman's canals run obliquely and interconnect Haversian canal.

(9) Haversian canal never contains lymph vessel.

(10) Most of the mature human bones whether compact or cancellous, are composed of thin plates of bony tissue called lamellae. They are called lamellar bone. Lamellae are concentric and form a system called osteon or Haversian system.

(11) Osteons are absent in spongy bones.

(12) Formation of bone is called osteogenesis or ossification.

Types of bone: According to shape:

(1) Long bones: With one diaphysis and two epiphysis.

(2) Short bones: Usually cuboid, cuneiform or trapezoid.

(3) Flat bones: e.g. scapula etc.

(4) Irregular bones: e.g. vertebrae etc.

(5) Pneumatic bones: e.g. maxilla etc.

(6) Sesamoid bones: e.g. patella, pisiform, fabella etc.

(7) Supernumerary: e.g. Os trigonum etc.

According to development:

(1) Membrane bones: Also called dermal bones. e.g. facial bone.

A defect in membranous ossification causes a syndrome called "cleidocranial dyrostosis".

(2) Cartilaginous bone: Ossifies in cartilage. e.g. bones of limbs, vertebral columns etc.

A defect in endochondral ossification causes a syndrome called "achondroplasia ".

(3) Membrano-cartilaginous bone: Ossifies partly in membrane and partly in cartilage. e.g. clavicle, temporal etc.

Law of ossification: Secondary centres of ossification which appear first, are last to unite.

Maintaining the shape of bone and removal of the unwanted part of bone by osteoclasts is called remodelling of bone.

Parts of a young bone: A typical bone ossifies in three parts - the shaft from primary centre and two ends from secondary centre. Before ossification, the bone has-

(1) Epiphysis: These are the ends and tips of the bone which ossifies from secondary centre. They may be pressure epiphysis which take part in articulation, traction epiphysis which does not take part in articulation and atavistic epiphysis. Atavistic epiphysis is phylogenetically an independent bone which is fused with another bone. e.g. Os trigonum.

(2) Diaphysis: It is long shaft of a bone which is ossified from primary centre.

(3) Metaphysis: These are the epiphysial end of the diaphysis. They are zone of active growth and have a rich supply of blood vessels and nerves.

(4) Epiphysial plate of cartilage: Cells of this plate are responsible for the lengthwise growth of the bone. After epiphysial fusion, no growth can occur.