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Microscopic Structure of Bone

Microscopic Structure of Bone - Spongy Bone Consists of...

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Microscopic Structure of Bone: Compact bone Microscopically, compact bone is riddled with canals and passageways that serve as conduits for nerves, blood vessels, and lymphatic vessels. The structural unit of compact bone is called the osteon or Haversian system. Each osteon is an elongated cylinder oriented along the long axis of the bone. Osteons appear as tiny weight-bearing pillars composed of a group of hollow tubes of bone matrix, one placed inside the next. Each of the tubes is called a lamella. All the collagen fibers in a particular lamella run in a single direction, while the collagen fibers in adjacent lamella always run in different directions resulting in a very strong structure able to withstand twisting and other mechanical stresses. Running through the core of each osteon is a canal (central or Haversian canal) which contains small blood vessels and nerve fibers. Running a right angles to the long axis are canals (perforating or Volkmann's canals) which connect the vascular and nerve supplies of the periosteum to those in the central canals and medullary cavity.
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Unformatted text preview: Spongy Bone Consists of trabeculae which are positioned where the bone is stressed. Only a few layers thick, the trabeculae contain irregularly arranged lamellae and osteocytes interconnected by canaliculi. No osteons are present. Chemical Composition of Bone: Bone is made of both organic and inorganic components. The organic components consist of cells and the osteoid (organic part of the matrix). The osteoid makes up 1/3 of the matrix, which contributes to the bone's structure, flexibility and tensile strength. The inorganic components consist of hydroxyapatites (mineral salts), largely calcium phosphate. Calcium salts are present in the form of tiny crystals, which accounts for bones hardness. Bone Markings: Bones are rarely smooth. They display bulges, depressions and holes. These markings are named in different ways. Projections that grow outward from the bone surface include heads, trochanters, spines, etc. Depressions and openings are fossae, sinuses, foramina, and grooves....
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