Bone architecture: Terminologies

Compact bone

• They are found on the outer part (wall) of the shafts of long bones.
• They are also called dense bones or cortical bones.
• Trabeculae in compact bones are thick and densely packed.

Spongy bone

• They are also called cancellous bone .
• They can be found in the ends of the long bone.

• The spongy bone at the bone ends is covered by a thin layer of compact bone.
• The trabeculae are thin and spread out in a mesh work.

Harvesian canal

• They are the microscopic canal seen in the cortical bones.
• These allows the blood vessels and nerves to travel through them.

Volkmann's canal

• They are also called perforating channels.
• They are small channels that runs between two harvesian canals thereby connects two osteon.
• They transmitted blood vessels from periosteum into bones.
• They provide energy and nourishing elements for osteon.

Osteoprogenital cells

• They are the stem cells that proliferate and convert into osteoblast.

Osteoblast

• They are the bone producing cells .

Osteocytes

• They are the cells of the mature bones.
• They are the osteoblast trapped in matrix that they secret.
• They are found in the lacunae.

Osteoclast

• These are the bone removing cells.

Lacunae

• Small cavity or gap between the two lamellae of the bone.
• It contains osteocytes.

Osteon

• Structural unit of compact bone.
• It is cylindrical in shape.
• Also called harvesian system.

Lamellae

• They are the layers of the compact bone tissue.
• The concentric layers of bone tissue that surrounds the harvesian canal is called concentric lamellae.
• They keeps the adjacent cells together.
• The irregular shaped bone tissue seen between the two osteons is called interstitial lamellae.
• The bone tissue that runs parallel to the periosteum is called circumferential lamellae.

Canaliculi

• Channels connecting the lacunae .
• Helps in the conduction of nutrients to osteocytes and waste products away from osteocytes.