Biology · Ch 10 — Animal Tissue
Bone
Bone
Bone is the other member of the supporting connective tissue group, distinguished by a hard matrix called ossein, which is built from the mineral salt hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). An outer tough membrane, the periosteum, encloses this matrix; blood vessels and nerves pierce through the periosteum to reach the bone tissue within.
The matrix itself is laid down in the form of concentric rings called lamellae. Each lamella carries fluid-filled cavities called lacunae, and fine canals called canaliculi radiate outward from each lacuna; the canaliculi of neighbouring lamellae connect with one another as they run through the matrix, forming a continuous network. Within the lacunae are found osteoblasts (the active, bone-forming cells), osteocytes (mature, inactive bone cells) and osteoclasts (cells responsible for breaking down bone matrix). Mammalian bone shows a distinctive arrangement called the Haversian system, in which a central Haversian canal, carrying an artery, a vein and nerves, runs through the middle of each set of concentric lamellae.
According to how this matrix is arranged, two types of bone occur in the human body: …
What this figure shows. A cut-away block of a long bone shown at increasing magnification: the outer periosteum layer covering the bone surface, with perforating (Volkmann's) canals running in from the surface to connect with a central (Haversian) canal that runs along the bone's length carrying an arteriole, venule and nerve; around each central canal, matrix is laid down in concentric rings called lamellae (an osteon), each ring holding small lens-shaped lacunae joined to their neighbours by fine radiating canaliculi, with an osteocyte occupying each lacuna; a separate close-up shows the honeycomb-like trabeculae of spo …