Gross Anatomy of Bones

• Compact & Spongy Bone

  each bone has a dense outer layer that looks smooth + solid to the naked eye

  this external layer = compact bone

  internal to this = spongy bone/trabecular bone

  = a honeycomb of flat pieces = trabeculae

  in living bones the open spaces between trabeculae r filled w red/yellow bone marrow

  
• Structure of Short, Irregular & Flat Bones - Spongy & Compact

  short, irregular + flat bones share a similar patter:

  they all consist of thin plates of spongy bone covered by compact bone

  the compact bone is covered outside + inside by connective tissue membranes - periosteum + endosteum
• Structure of Short, Irregular & Flat Bones - Shafts & Bone Marrows

  these bones r not cylindrical + so they have no shaft/expanded ends

  they contain bone marrow between their trabeculae, but no well-defined marrow cavity

  where they form movable joints w their neighbours, hyaline cartilage covers their surfaces
• Structure of a Typical Long Bone

  w a few exceptions, all long bones have the same general structure:

  a shaft (diaphysis)

  bone ends (epiphyses)

  membranes

  
• Structure of Long Bones - Diaphysis

  a tubular diaphysis/shaft forms the long axis of the bone

  it's constructed of a relatively thick collar of compact bone that surrounds a central medullary cavity (marrow cavity) that contains no bone tissue

  the medullary cavity contains yellow marrow (fat)

  between the marrow + the compact bone = thin layer of spongy bone
• Structure of Long Bones - Epiphyses

  the epiphyses r the bone ends

  an outer shell of compact bone forms the epiphysis exterior + the interior contains spongy bone

  a thin layer of articular (hyaline) cartilage covers the joint surface of each epiphysis, cushioning the opposing bone ends during movement + absorbing stress
• Structure of Long Bones - Epiphyseal Line

  between the diaphysis + each epiphysis of an adult long bone is an epiphyseal line, a remnant of the epiphyseal plate

  = growth plate = a disc of hyaline cartilage tat grows during childhoos to lengthen the bone
• Structure of Long Bones - Metaphysis


  the flared portion of the bone where the diaphysis + epiphysis meet, whether it is the epipyseal plate/line
• Structure of Long Bones - Periosteum

  periosteum = a white, double-layered membrane that covers the external surface of the entire bone except the joint surfaces

  has an outer fibrous layer + a inner osteogenic layer
• Periosteum - Outer Layer

  the outer fibrous layer of the periosteum is dense irregular connective tissue
• Periosteum - Inner Osteogenic Layer

  the inner osteogenic layer of the periosteum, next to the bone surface, contains osteoprogenitor cells (stem cells that give rise to most bone cells)

  it also has bone-destroying cells (osteoclasts) + bone-forming cells (osteoblasts)
• Periosteum - Rich Supply of Nerve Fibres & Blood Vessels

  the periosteum is richly supplied w nerve fibres + blood vessels, which is why broken bones r painful + bleed profusely
• Periosteum - Perforating Fibres

  perforating fibres = bundles of collagen fibres that extend into the bone matrix

  = secure the periosteum to the underlying bone

  the periosteum also provides anchoring points for tendons + ligaments

  at these points, the perforating fibres r really dense
• Structure of Long Bones - Endosteum

  endosteum = a delicate connective tissue membrane that covers the internal bone surfaces

  covers the trabeculae of the spongy bone + lines the canals that pass thru the compact bone

  the endosteum contains the same cells cell types as the inner layer of the periosteum