Bone Intro and Anatomy

• Skeletal system is composed of

  • Bones
  • Cartilage
  • Ligaments
• Functions of the skeletal system

  • Support
  • Protection
  • Movement
  • Electrolyte balance (calcium & phosphate storage/release)
  • Acid-base balance (alkaline phosphate & carbonate salts storage/release)
  • Blood cell production (hematopoiesis)
• Bone (osseous) tissue

  Connective tissue that undergoes mineralization/calcification - a hardening process with a hard matrix of deposited calcium phosphate (Ca3(PO4)2)
• Components of bone (organ)

  • Bone (tissue)
  • Bone marrow
  • Blood
  • Cartilage
  • Adipose tissue
  • Nervous tissue
  • Fibrous connective tissue
• Categories of bone anatomy

  • Compact bone
  • Spongy bone
• Compact bone


  • Dense outer shell of bones
• Spongy bone


  • Loosely organized bone tissue covered by compact bone
• Flat, short, and irregular bones

  • Compact bone on outside for protection
  • Spongy bone on inside to absorb shock (called "diploe" in cranial bones)
  • Bone marrow between trabeculae
• Parts of a long bone

  • Diaphysis (shaft)
  • Epiphysis (enlarged end(s))
  • Metaphysis (where diaphysis meets epiphysis)
• Diaphysis of long bones

  • Contains medullary cavity (marrow cavity) with bone marrow
• Epiphysis of long bones

  • Anchors ligaments and tendons
  • Contains spongy bone enclosed by compact bone
• Articular cartilage


  • Hyaline cartilage that covers joint surface to allow more free movement and absorb shock
• Nutrient foramina


  • Minute holes in bone that allow blood vessels and nerves to penetrate
• Epiphyseal plate (growth plate)


  • Area of hyaline cartilage that enables lengthening of bone
  • In adults, becomes an epiphyseal line where the plate was
• Layers of the diaphysis

  • Periosteum
  • Compact bone
  • Spongy bone
  • Endosteum
  • Medullary cavity
• Periosteum


  • Connective tissue covering the outer bone surface with a fibrous outer layer and an osteogenic cell layer
  • Protects, supports vessels and nerves, connects to other tissues, and facilitates growth and repair
• Endosteum


  • Thin layer of reticular connective tissue lining the marrow cavity, Haversian canals, and spongy bone surfaces
  • Houses osteogenic cells, osteoblasts, and osteoclasts to facilitate growth, repair, and remodeling
• Medullary cavity


  • Contains yellow bone marrow, which is mostly adipose tissue and serves as an energy reserve (does not produce blood cells)
• Types of bone marrow

  • Red marrow (produces blood cells)
  • Yellow marrow (in long bones of adults)
• Osteogenic cells


  • Stem cells that create osteoblasts, located in the endosteum and periosteum
• Osteoblasts


  • Secrete the organic portions of the bone matrix, become trapped in the matrix and transform into osteocytes
• Osteocytes


  • Maintain the bone matrix, respond to bone density needs and blood calcium/phosphate levels, some resorb matrix while others deposit it, respond to physical stress on bone, and release signaling molecules to allow for bone remodeling
• Osteoclasts


  • Dissolve and remove old, damaged bone tissue through resorption, secrete acid and enzymes, develop from bone marrow stem cells (not osteogenic cells), and are large cells with multiple nuclei
• Bone matrix


  A composite material consisting of a ceramic (inorganic) portion of hydroxyapatite crystals that impart hardness, and a polymer (organic) portion of collagen fibers and ground substance synthesized by osteoblasts that impart flexibility
• Mineral deficiency can cause rickets, and insufficient collagen production can cause osteogenesis imperfecta (brittle bone disease)
• Osteon


  • The structural unit of compact bone, consisting of a central (Haversian) canal surrounded by concentric lamellae
• Lamellae


  • Weight-bearing columns of bone matrix arranged in concentric rings
• Central (Haversian) canal

  • Spaces that allow blood vessels and nerves to pass through compact bone
• Perforating canals

  • Canals that are perpendicular to the central canals and connect them to the periosteum
• Spongy bone anatomy

  • Composed of spicules (slivers/spines) and trabeculae (plates) that are organized along stress lines to provide strength and resistance in multiple directions