Bone Tissue (PowerPoint)

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					Chapter 7
      Bone Tissue
• Know the functions of the skeletal system

• Understand how bones are classified

• Identify the macroscopic and microscopic features of bone

• Understand how bone is developed and physiologically

• Know what a fracture is and how it is repaired

• Know some bone disorders
                      Skeletal System
• Composed of bones, cartilages, and ligaments joined tightly
  together to form a strong, flexible framework for the body

• Skeleton functions
   –   Support
   –   Protection
   –   Movement
   –   Electrolyte balance
   –   Acid-base balance
   –   Blood formation

• Osseous tissue               

   – Connective tissue with a hardened matrix
        • Deposition of calcium phosphate and other minerals
   – Part of the composition of a bone
         Classification of Bones
• Classified based on shape and corresponding

• Four categories
  – Long bones
  – Short bones
  – Irregular bones
  – Flat bones

        General Features of Bones
• Epiphysis
   – Ends of the bone
   – Composed of cancellous (spongy) bone

• Diaphysis
   – Shaft of the bone
   – Composed of compact bone

• Medullary cavity
   – Contains yellow bone marrow

   – Epiphyiseal plate

Structure of Bone

                    Figure 5.1
• Four main types of bone cells                   • Matrix
    – Osteogenic (osteoprogenitor) cells             – composed of inorganic and organic
        • give rise to osteoblasts , osteocytes        components

    – Osteoblasts
        • Bone-forming cells
        • Found along endosteum and               • Inorganic component
          periosteum                                 – Hydroxyapaptite
        • Secrete osteocalcin                            • Composed mainly of CaPO4 salt

    – Osteocytes
        • Former osteoblasts that have been
          trapped in their lacunae
        • Maintain bony matrix
                                                  • Organic components
        • Strain sensors                             – Protein and carbohydrate
                                                         • Collagen

    – Octeoclasts                                 • Bone is a composite
        • Bone-dissolving cells
                  Compact Bone
• Osteon (haversian system)
   – Basic structural unit of compact

• Central (haversian) canal
  surrounded by concentric
  lamellae (matrix)

• Perforating canals
   – Transverse or diagonal passages

     into the central canal
   – Originate at nutrient foramen
               Spongy Bone
• Composed by a network of
  spicules and trabeculae

• Spaces filled with red

• Beams arranged to sustain
           Bone Development
• Ossification or osteogenesis
  – Formation of bone

• Two methods
  – Intramembranous ossification

  – Endochondral ossification
     Intramembranous Ossification
• Produces flat bones of skull and clavicles

• Starts with

• End with

      Endochondral Ossification
• Bone develops from a hyaline model

   Bone Growth and Remodeling
• Bone Elongation
  – Involves epiphyseal plates
       • Hyaline cartilage between to transitional zones (metaphysis)

• Zones of mataphysis
  –   Reserve cartilage
  –   Cell proliferation
  –   Cell hypertrophy
  –   Calcification
  –   Bone deposition
       • Spongy bone
    Bone Growth and Remodeling
• Interstitial growth
   – Result from growth of cartilage within the metaphysis
   – Finite process
      • Epiphyseal line

• Appositional growth
   – Growth in diameter and thickness
      • Circumferential lamellae

• Remodeling
   – Wolff’s law of bone
      • The architecture of bone is determined by the mechanical stresses
        placed up it.
          – Bone adapts to withstand stress
    Physiology of Osseous Tissue
• Mineral deposition
  – Calcium and phosphate are allowed to reach their
    solubility product
     • Precipitate in the matrix
  – Ectopic ossification
     • Abnormal calcification of soft tissue
         – Calculus

• Mineral resorption
  – HCl secreted by osteoclasts
  – Acid phosphatase
     • Absorbs collagen
          Calcium Homeostasis
• Hypocalcemia
  – Leads to excitability of nervous system

• Hypercalcimia
  – Leads to depression of nervous system
               Calcium Homeostasis
• Regulated by three hormones
   – Calcitonin
       • Secreted by parafollicular cells in thyroid
       • Promote deposition of calcium in the bone
       • Decreases calcium level in blood
           – Inhibit osteoclasts, promote osteoblast activity
   – Parathyroid hormone
       • Secreted by parathyroid glands
       • Promotes bone resorption
       • Increases calcium level in blood
           –   Raise osteoclast population
           –   Promotes calcium reabsorption in kidneys
           –   Promotes calcitriol synthesis
           –   Inhibits collagen deposition
   – Calcitriol
       • Increases calcium level in blood
           – Promotes more calcium absorption by intestine
           – Promotes reapsorption from skeleton
              Fractures and Repair
• Fracture
  – Break in the bone
  – Two types
     • Stress
     • Pathological
     • Table 7-2 for classifications

• Granulation tisssue
  – Fibrous mass of
    capillaries and cells
    within hematoma
                 Bone Disorders
• Osteoporosis
  – Sever loss of bone density
     • Osteoclast more active than osteoblasts

• Osteosarcoma
  – Most common and deadly form of bone cancer
     • Metastasizes quickly

• Osteogenesis imperfecta
  – Brittle bones
     • Defect in collagen deposition

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