Bones

• Diaphysis


  The tubular shaft that runs between the proximal and distal ends of a long bone
• Medullary cavity


  The hollow region in the diaphysis, filled with yellow marrow
• Compact bone


  The dense and hard walls of the diaphysis
• Epiphysis


  The wider section at each end of a long bone, filled with spongy bone and red marrow
• Metaphysis


  The narrow area that contains the epiphyseal plate, a layer of hyaline cartilage in a growing bone
• Epiphyseal plate


  A layer of hyaline cartilage in a growing bone
• Epiphyseal line


  Where the epiphyseal plate was located after the bone stops growing in early adulthood
• Endosteum


  The delicate membranous lining of the medullary cavity, where bone growth, repair, and remodeling occur
• Periosteum


  The fibrous membrane that covers the entire outer surface of bone, except where the epiphyses meet other bones to form joints
• Articular cartilage


  The thin layer of cartilage that covers the epiphyses where they meet other bones to form joints
• Diploë


  The layer of spongy bone between the two layers of compact bone in flat bones like the cranium
• Bone markings

  • Articulations
  • Projections
  • Holes
• Articulation


  Where two bone surfaces come together
• Projection


  An area of a bone that projects above the surface, for attachment of tendons and ligaments
• Hole

  An opening or groove in the bone that allows blood vessels and nerves to enter
• Bone contains a relatively small number of cells entrenched in a matrix of collagen fibers that provide a surface for inorganic salt crystals to adhere
• The hydroxyapatite crystals give bones their hardness and strength, while the collagen fibers give them flexibility so that they are not brittle
• Bone cells

  • Osteoblasts
  • Osteocytes
  • Osteogenic cells
  • Osteoclasts
• Osteoblast


  The bone cell responsible for forming new bone, found in the growing portions of bone
• Osteocyte


  The primary cell of mature bone, formed when osteoblasts become trapped within the calcified matrix
• Osteogenic cell

  Undifferentiated cells with high mitotic activity that can differentiate into osteoblasts
• Osteoclast


  The cell responsible for bone resorption or breakdown, found on bone surfaces
• Osteoblasts and osteocytes are incapable of mitosis, so osteogenic cells replenish them when old ones die
• Canaliculi


  Channels within the bone matrix
• If osteoblasts and osteocytes are incapable of mitosis, then how are they replenished when old ones die?
• Osteogenic cells

  Undifferentiated with high mitotic activity, the only bone cells that divide, they differentiate and develop into osteoblasts
• Osteoclasts


  Cell responsible for bone resorption, or breakdown, found on bone surfaces, multinucleated, originate from monocytes and macrophages, not from osteogenic cells
• Osteoclasts are continually breaking down old bone while osteoblasts are continually forming new bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone.
• Bone Cells

  • Osteogenic cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteogenic cells


  Develop into osteoblasts
• Osteoblasts

  Bone formation
• Osteocytes


  Maintain mineral concentration of matrix
• Osteoclasts

  Bone resorption
• Compact bone

  Dense, stronger of the two types of bone tissue, found under the periosteum and in the diaphyses of long bones, provides support and protection
• Osteon


  Microscopic structural unit of compact bone, composed of concentric rings of calcified matrix called lamellae, with a central canal containing blood vessels, nerves, and lymphatic vessels
• Canaliculi

  Connect the lacunae and eventually with the central canal, allowing nutrients to be transported to the osteocytes and wastes to be removed
• Spongy (Cancellous) bone


  Contains osteocytes housed in lacunae in a lattice-like network of matrix spikes called trabeculae, provides balance to the dense and heavy compact bone by making bones lighter so that muscles can move them more easily, contains red marrow where hematopoiesis occurs
• Trabeculae


  Matrix spikes in spongy bone, form along lines of stress to provide strength
• Nutrient foramen

  Small openings in the diaphysis through which arteries pass to provide nourishment to the spongy bone and medullary cavity
• Nerves follow the same paths as blood vessels into the bone, concentrating in the more metabolically active regions