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2012-09-30 23:52:37
ANAT390 cartilage bone

ANAT 390 Lecture 11 Cartilage and Bone
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  1. What are the five key similarities between cartilage and bone?
    • Both are specialized forms of CT
    • Both share a mesenchymal origin
    • Both contain cells embedded in a matrix (ECM) that they have produced (in lacunae)
    • The functions of both rely on the composition/structure of their ECM's
    • Both are covered with a thin layer of dense irregular connective tissue that is protective and may contain progenitor/stem-like cells
  2. Define periosteum.
    The thin layer of dense irregular connective tissue that covers bone.
  3. Define perichondrium.
    The thin layer of dense irregular connective tissue that covers cartilage.
  4. Name three features of progenitor type cells.
    • In perichondrium/osteum
    • Stem-like
    • Lineage-restricted
  5. Name two features of "blast" type cells.
    • Start to differentiate
    • Lay down matrix
  6. Name two features of "cyte" type cells
    • Terminally differentiated
    • Trapped in matrix/lacunae
  7. Name the three key differences between cartilage and bone.
    • Cartilage ECM is a firm, hydrated, plastic-like gel with a high diffusion index (lots of proteoglycans), while bone ECM is solid and mineralized (calcium phosphate)  with a low diffusion index.
    • Cartilage is avascular while bone is richly vascularized
    • After trauma or injury, repair and regeneration is much greater in bone than cartilage.
  8. What are the three primary functions of cartilage?
    • 1) Support for soft tissue
    • 2) Sliding/Low frictional surfaces in joints
    • 3) Growth (epiphyseal) plate of long bones

  9. What type of tissue is this?
    Hyaline Cartilage
  10. Describe the structure of hyaline cartilage.
    • Most abundant type of cartilage; found in joints, nose, and trachea
    • Has translucent/glassy appearance
    • Usually has a perichondrium; but lower regenerative capacity than bone
    • Entirely organic (not mineralized)
    • 70% water
    • 20% collagen - most often Type II
    • 10% proteoglycan
    • Very hydrated, resists compression, has some tensile strength

  11. What tissue type is this?
    Elastic cartilage
  12. Describe the structure of elastic cartilage.
    • similar to HC
    • Contains elastic fibers which impart greater flexibility
    • Chondrocytes are more abundant and larger than in HC
    • Less matrix than HC
    • Well-defined perichondrium containing elastic fibers
    • found in ear pinna

  13. What tissue type is this?
  14. Describe the structure of fibrocartilage.
    • distinct from HC and EC
    • matrix contains thick bundles of Type I collagen - provides high tensile strength
    • No distinct perichondrium - little or no ability to regenerate
    • Resembles dense regular connective tissue, except FC contains chondrocytes in lacunae and fibroblasts
    • found in intervertebral disks and at sites of bone attachment
    • Resistant to compression
  15. What are the two components of the ECM of bone?
    • 1) Organic component = osteoid
    • 2)  Inorganic component = mineralized
  16. Name 4 features of the organic component of bone ECM.
    • low amount of ground substance
    • high amount of Type I collagen fibers
    • low amount of diffusion
    • deposited first by osteoblasts
  17. Name 5 features of the inorganic component of bone ECM.
    • consists of hydroxyapatite crystals (high calcium high phosphate)
    • rigid
    • very low amount of diffusion
    • deposited late by osteoblasts and trapped osteocytes (crystals form on collagen fibers extracellularly)
    • facilitated by the enzyme alkaline phosphatase which can enter the bloodstream (useful serum-marker)
  18. What is a spicule?
    a small connected piece of bone tissue
  19. What is an osteoblast?
    usually on the edges of bone tissue, lays down osteoid initially, derived from osteogenic cells
  20. What is an osteocyte?
    Within/encased/trapped in bone tissue lacunae; lays down mineralized crystals; derived from osteoblasts
  21. What is an osteoclast?
    large, multinucleate cell; derived from hematopoeitic stem cells; can digest/reabsorb/destroy bone matrix; important for bone remodelling/repair and for controlling blood levels of calcium
  22. Explain the four steps to osteoclast function.
    • 1.  Cells adhere to bone very tightly via focal adhesions around the periphery of the cell with actin filaments emanating from them; form a central sealing zone where bone digestion/reabsorption will occur
    • 2.  Cells generate carbonic acid (H2CO3) using the cytoplasmic enzyme carbonic anhydrase.
    • 3.  Cells release protons via transmembrane channels onto the bone surface inside the sealing zone - acid degrades hydroxyapatite which releases calcium, picked up by capillaries to raise serum calcium levels.
    • 4.  Cells release lysosomal enzymes and metalloproteases that digest collagen and osteoid.
  23. What is osteoclast function stimulated by?
    Osteoblasts due to parathyroid hormone.
  24. What is osteoclast function inhibited by?
    Calcitonin (hormone) and bisphosphonates (drug = fosamax)

  25. What tissue type is this?
    Spongy bone

  26. What tissue type is this?
    Compact bone
  27. Describe the structure of compact bone.
    • Bone matrix is arranged in concentric layers (=lamellae) arranged around a central canal
    • Forms cylindrical columns of bone tissue (=osteon) with central/vertical Haversian canals for blood vessels; there are also horizontal Volkmann canals for blood vessels
  28. Name and describe the two methods of bone formation?
    • 1) Intramembranous Bone Formation (flat bones of the skull):
    • mesenchyme condenses; mesenchymal stem cells generate cells of the osteogenic lineage
    • bone forms directly within the mesenchymal condensations
    • 2) Endochondral Bone Formation (all other bones):
    • a hyaline cartilage model of the bone forms first
    • blood vessels invade the cartilage and drag in osteoprogenitor cells (=periosteal bud)
    • increased oxygen tension due to vascularization leads to calcification of cartilage followed by chondrocyte cell death; bone tissue is laid down in its place (=ossification centre)
    • ossification centers form centrally in the shaft of long bones (=diaphysis) at the primary ossification center and at the ends (=epiphysis) at secondary ossification centers
    • reserve cartilage remains between the diaphysis and epiphyses (=growth/epiphyseal plate)
    • growth plate expands until early adulthood to increase the size of long bones
  29. Describe osteoarthritis.
    • Very common disease, characterized by defects in articular/hyaline cartilage within the joint
    • Causes include injury or wear and tear
    • Cartilage has little regenerative repair and there is no cure, so severely affected joints need to be replaced.
  30. Define osteoporosis.
    • Increase in bone porosity
    • 50% incidence is women > 50 years
    • Increased risk of fracture
    • Bone remodeling is skewed towards greater reabsorption
    • Treatment options include anti-resorptives and anabolics to decrease the activity of osteoclasts