An osteon is a fundamental unit of compact bone, which forms the dense outer layer of most bones. It is a cylindrical unit.
Anatomy of an Osteon
At its center is the Haversian canal, which runs longitudinally through the osteon. This central canal contains blood vessels, nerves, and lymphatic vessels, providing essential supplies to the surrounding bone tissue.
Surrounding the Haversian canal are concentric lamellae, layers of bone matrix. These lamellae are made of both organic components, such as collagen fibers, and inorganic mineral salts, like hydroxyapatite crystals, contributing to the bone’s hardness and rigidity. Within these lamellae are small spaces called lacunae, which house mature bone cells known as osteocytes.
Tiny channels, called canaliculi, radiate outwards from each lacuna, connecting them to neighboring lacunae and ultimately to the central Haversian canal. These channels allow osteocytes to extend their cellular processes and communicate with each other. This network also facilitates the transport of nutrients and the removal of waste products throughout the osteon.
Osteons in Bone Structure
Osteons are the primary structural units of compact bone, which forms the hard, dense outer shell of bones. These units typically run parallel to the long axis of the bone. This arrangement contributes to the bone’s ability to withstand stress.
While osteons themselves contain Haversian canals, there are also perforating canals, known as Volkmann’s canals, that connect adjacent Haversian canals. These canals run perpendicular or obliquely to the Haversian canals, creating a broader network for blood vessels, nerves, and lymphatic vessels to extend across the compact bone. Volkmann’s canals also connect the blood supply of the Haversian canals to the periosteum, the membrane covering the outer surface of the bone.
Role of Osteons in Bone Health
The structure of osteons is fundamental to maintaining bone health. The concentric arrangement of lamellae provides mechanical strength, allowing bone to resist bending and twisting forces. This layered organization helps distribute stress effectively, making the bone less prone to fracturing.
The Haversian system, encompassing the central canal, lacunae, and canaliculi, plays a crucial role in bone cell health. Blood vessels within the Haversian canals deliver oxygen and nutrients to the osteocytes, which are embedded deep within the mineralized matrix. Simultaneously, the canaliculi network enables the removal of metabolic waste products from these cells. This continuous supply and removal system supports bone maintenance, repair, and its ability to adapt to mechanical demands.