structure of bones

• structure of long bone

  A) epiphysis

  B) diaphysis

  C) epiphysis

  D) cartilage

  E) cartilage

  F) spongy bone

  G) medullary cavity

  H) red marrow

  I) compact bone

  J) periosteum

  K) yellow marrow

  
• diaphysis is the shaft making up the main portion of the bone.
• when cut lengthwise, the diaphysis is seen to be a hollow cylinder made of compact bone surrounding the medullary cavity. the cavity is used as a fat storage site and often called the yellow bone marrow cavity.
• epiphysis are the enlarged ends of the bone
• the epiphysis is covered with a thin layer of cartilage called the articular cartilage. it is made of compact bone on the outside with the central region containing spongy bone. it contains many large spaces filled with marrow, which may be where red marrow in certain bones
• periosteum is the dense, white, fibrous outer covering of the bone
• there is no periosteum at the joints where the bone is covered with articular cartilage
• compact bone is made of many similar units called osteons. they run parallel to the long axis of the bone, maximising the strength of the bone
• osteons contain :

  • central canal at its centre
  • lamellae, concentric layers of bony matrix surrounding the central canal
  • lacunae, small spaces of matrix between lamellae
  • osteocytes which are bone cells occupying each lacuna
  • canaliculi, tiny canals that run between lacunae
  • projections from bone cells entering canaliculi which makes contact with adjacent bone cells, allowing materials to be passed from cell to cell
  • at least one blood capillary and possibly nerves and lymph capillaries. they are located in the central canal
• spongy bone is made up of an irregular arrangement of thin, bony plates called trabeculae. spaces in the trabeculae are occupied by bone cells. nerves and blood vessels pass through the irregular spaces in the matrix.