Structure of Long Bones

Diaphysis: the shaft that makes up most of the bones length and is composed of compact bone
Periosteum: the fibrous connective tissue membrane that covers and protects the diaphysis 
Perforating/Sharpey's Fibers: hundreds of connective fibers that secure the periosteum to the underlying bone
Epiphyses: the ends of the long bone ~ each epiphyses consists of a thin layer of compact bone enclosing an area filled with spongy bone
Articular Cartilage: (instead of periosteum) this covers the external surface of bones ~ because it is glassy hyaline cartilage, it provides a smooth, slippery surface that decreases friction at joint surfaces 
Epiphyseal Line: the line of bony tissue spanning the epiphysis that looks a bit different from the rest of the bone in that area ~ it is a remnant of the epiphyseal plate
Epiphyseal Plate: a flat plate of hyaline cartilage (seen in young, growing bone) that cause the lengthwise growth of a long bone ~ after puberty, the epiphyseal plate is replaced by bone, leaving only the epiphyseal lines to mark their previous location
Yellow Marrow or Medullary, Cavity: the cavity of the shaft that is used for storage of adipose (fat) tissue
Red Marrow: the substance found in bone cavities in infants ~ in adults, red marrow is confined to the cavities of spongy bone of flat bones and the epiphyses of some long bones
Bone Markings: the bumps, holes, and ridges that mark the outside of a bone and translate where muscles, tendons, and ligaments were attached/where blood vessels and nerves passed ~ the two categories of bone markings are projections/processes and depressions/cavities 
Osteocytes: mature bone cells
Lacunae: tiny cavities within the matrix where osteocytes can be found
Lamellae: the concentric circles that the lacunae form
Central (Haversian) Canals: what the lamellae form around ~ these canals run lengthwise through the bony matrix, carrying blood vessels and nerves to all areas of the bone
Osteon/Haversian System: each complex consisting of central canal and matrix rings
Canaliculi: tiny canals that radiate outward from the central canals to all lacunae ~ the canaliculi form a transportation system that connects all the bone cells to the nutrient supply through the hard bone matrix
Perforating (Volkmann's) Canals: canals that run into the compact bone at right angles to the shaft in order to create communication pathways from the outside bone to its interior (and the central canals)

The calcium salts deposited in the matrix give bone its hardness, whereas the organic parts (especially the collagen fibers) provide for bone's flexibility and great tensile strength.



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