bonehisto

• Functions of bone tissue

  • Support
  • Protection (protect internal organs)
  • Movement (provide leverage system for skeletal muscles, tendons, ligaments and joints)
  • Mineral homeostasis (bones act as reserves of minerals important for the body like calcium or phosphorus)
  • Hematopoiesis: blood cell formation
  • Storage of adipose tissue: yellow marrow

  
• Shapes of bones


  • Long bones (e.g., humerus, femur)
  • Short bones (e.g., carpals, tarsals, patella)
  • Flat bones (e.g., parietal bone, scapula, sternum)
  • Irregular bones (e.g., vertebrae, hip bones)

  
• Parts of a long bone

  • Diaphysis: long shaft of bone
  • Epiphysis: ends of bone
  • Epiphyseal plate: growth plate
  • Metaphysis: b/w epiphysis and diaphysis
  • Articular cartilage: covers epiphysis
  • Periosteum: bone covering (pain sensitive)
  • Sharpey's fibers: periosteum attaches to underlying bone
  • Medullary cavity: Hollow chamber in bone
  • Endosteum: thin layer lining the medullary cavity

  
• Blood and nerve supply of bone


  • Periosteal arteries accompanied by nerves supply the periosteum and compact bone
  • Epiphyseal veins carry blood away from long bones
  • Nerves accompany the blood vessels that supply bones
  • The periosteum is rich in sensory nerves sensitive to tearing or tension
• Compact bone


  Dense outer layer

  
• Spongy bone


  Honeycomb of trabeculae (needle-like or flat pieces) filled with bone marrow

  
• Compact bone (osteon)


  • Lamellar bone (groups of elongated tubules called lamella)
  • Majority of all long bones
  • Protection and strength (wt. bearing)
  • Concentric ring structure
  • Blood vessels and nerves penetrate periosteum through horizontal openings called perforating (Volkmann's) canals

  
• Components of compact bone (osteon)


  • Central (Haversian) canals run longitudinally. Blood vessels and nerves.
  • Concentric lamella around the canals
  • Osteocytes occupy lacunae which are between the lamella
  • Radiating from the lacunea are channels called canaliculi (finger like processes of osteocytes)

  
• Spongy bone (cancellous bone)


  • Trabecular bone tissue (haphazard arrangement)
  • Filled with red and yellow bone marrow
  • Osteocytes get nutrients directly from circulating blood

  
• Cells of bone tissue

  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts

  
• Osteoprogenitor cells


  • Derived from mesenchyme
  • Unspecialized stem cells
  • Undergo mitosis and develop into osteoblasts
  • Found on inner surface of periosteum and endosteum
• Osteoblasts


  • Bone forming cells
  • Found on surface of bone
  • No ability to mitotically divide
  • Collagen secretors

  
• Osteocytes


  • Mature bone cells
  • Derived from osteoblasts
  • Do not secrete matrix material
  • Cellular duties include exchange of nutrients and waste with blood

  
• Osteoclasts


  • Bone resorbing cells
  • Found on bone surface
  • Responsible for growth, maintenance and bone repair

  
• Inorganic mineral salts in bone


  • Tricalcium phosphate in crystalline form called hydroxyapatite (Ca3(PO4)2(OH)2)
  • Calcium Carbonate (CaCO3)
  • Magnesium Hydroxide (Mg(OH)2)
  • Fluoride and Sulfate
• Components of skeletal cartilage


  • Chondrocytes: cartilage producing cells
  • Lacunae: small cavities where the chondrocytes are encased
  • Extracellular matrix: jellylike ground substance
  • Perichondrium: layer of dense irregular connective tissue that surrounds the cartilage

  
• Types of cartilage


  • Hyaline cartilage
  • Elastic cartilage
  • Fibrocartilage
• Hyaline cartilage


  • Most abundant cartilage
  • Provides support through flexibility
  • Found in articular cartilages, costal cartilage, larynx, trachea, and nose
• Elastic cartilage


  • Contains many elastic fibers
  • Able to tolerate repeated bending
  • Found in ear and epiglottis
• Fibrocartilage


  • Resists strong compression and strong tension
  • An intermediate between hyaline and elastic cartilage
  • Found in intervertebral discs and pubic symphysis
• Situations where bone formation occurs


  • Formation of bone in an embryo
  • Growth of bones until adulthood
  • Remodeling of bone
  • Repair of fractures

  
• Intramembranous ossification


  1. Ossification center appears in the fibrous connective tissue membrane

  2. Osteoblasts secrete bone matrix within the fibrous membrane

  3. Osteoblasts mature into osteocytes

  
• Endochondral ossification


  1. Enlarging chondrocytes within calcifying matrix. Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies

  2. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone

  3. Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center

  4. The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone

  5. Blood vessels invade the epiphyses and osteoblasts form secondary centers of ossification

  
• Longitudinal bone growth


  1. Cartilage continually grows and is replaced by bone

  2. Bones lengthen entirely by growth of the epiphyseal plates

  3. Cartilage is replaced with bone as quickly as it grows

  4. Epiphyseal plate maintains constant thickness

  
• Zones of bone growth under hGH


  • Zone of resting cartilage (quiescent)
  • Zone of proliferating cartilage (prolferation zone)
  • Zone of hypertrophic (maturing) cartilage
  • Zone of calcified cartilage

  
• Appositional bone growth


  1. Bone is resorbed at endosteal surface and added at periosteal surface

  2. Osteoblasts add bone tissue to the external surface of the diaphysis

  3. Osteoclasts remove bone from the internal surface of the diaphysis

  
• Bone remodeling


  1. Bone continually renews itself

  2. Osteoclasts are responsible for matrix destruction

  3. Spongy bone replaced every 3-4 years

  4. Compact bone every 10 years

  
• Fracture repair


  1. Blood clot will form around break (fracture hematoma)

  2. Inflammatory process begins

  3. Blood capillaries grow into clot

  4. Phagocytes and osteoclasts remove damaged tissue

  5. Procallus forms and is invaded by osteoprogenitor cells and fibroblasts

  6. Collagen and fibrocartilage turns procallus to fibrocartilagenous (soft) callus

  7. Broken ends of bone are bridged by callus

  8. Osteoprogenitor cells are replaced by osteoblasts and form spongy bone (bony callus)

  9. Callus is resorbed by osteoclasts and compact bone replaces spongy bone

  10. Remodeling: the shaft is reconstructed to resemble original unbroken bone
• Closed reduction - bone ends coaxed back into place by manipulation
• Open reduction - surgery, bone ends secured together with pins or wires
• growth of cartilage on the epiphyseal plate steps

  1/ zone of resting cartilage

  2/ zone of prolifirating cartilage ( prolifiration zone )

  3/ hyperthrophic (maturing) cartilage

  4/ zone of calcified cartilage
• Zone of resting cartilage (quiescent):

    - no bone growth

    - located near the epiphyseal plate

    - scattered chondrocytes
• Zone of resting cartilage (quiescent):

    - no bone growth

    - located near the epiphyseal plate

    - scattered chondrocytes

    - anchors plate to bone
• Zone of proliferating cartilage (prolferation zone)

     - chondrocytes stacked like coins

    - chondrocytes divide
• Zone of hypertrophic (maturing) cartilage

    - large chondrocytes arranged in columns

    - lengthwise expansion of epiphyseal plate
• Zone of calcified cartilage

    - few cell layers thick

    - occupied by osteoblasts and osteoclasts

      and capillaries from the diaphysis

    - cells lay down bone
• Zone of calcified cartilage

    - few cell layers thick

    - occupied by osteoblasts and osteoclasts

      and capillaries from the diaphysis

    - cells lay down bone

    - dead chondrocytes surrounded by a calcified

        matrix.
• Remodeling : the shaft is reconstructed to resemble original unbroken bone.  
• bone remodeling enables Ca to be pulled from bone when   blood levels are low