BIOL 121 Chp 6: The Skeletal System: Bone Tissue


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This is a lecture presentation for my BIOL 121 Anatomy and Physiology I students on Chapter 6: The Skeletal System: Bone Tissue (Principles of Anatomy and Physiology, 14th Ed. by Tortora and Derrickson).

Rob Swatski, Associate Professor of Biology, Harrisburg Area Community College - York Campus, York, PA. Email:

Please visit my website for more anatomy and biology learning resources:

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BIOL 121 Chp 6: The Skeletal System: Bone Tissue

  1. 1. 1 The Skeletal System: Bone Tissue BIOL 121: A&P IChapter 6 Rob Swatski Associate Professor of Biology HACC – York CampusTextbook images - Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
  2. 2. 2
  3. 3. 3 Skeletal System Tissues Bone Cartilage Dense CT Epithelium Adipose Nervous
  4. 4. 4
  5. 5. 5 Functions of Bone Supports body Protects soft tissues Muscle attachment site
  6. 6. 6 Functions of Bone, cont. Mineral storage & homeostasis Produces blood cells in red bone marrow (hemopoiesis aka hematopoiesis) Energy storage in yellow bone marrow
  7. 7. 7 Bone Marrow
  8. 8. 8
  9. 9. 9 Anatomy of a Long Bone
  10. 10. 10 Anatomy of a Long Bone Diaphysis Epiphysis Metaphysis Epiphyseal plate Articular cartilage
  11. 11. (b) Partially sectioned humerus Medullary cavity in diaphysis Compact bone Spongy bone Epiphyseal line Proximal epiphysis Metaphysis
  12. 12. 12 Anatomy of a Long Bone, cont. Medullary (Marrow) cavity Endosteum Periosteum: 2 layers A. Fibrous layer B. Osteogenic layer
  13. 13. 13
  14. 14. 14
  15. 15. 15 Histology of Bone Tissue Compact bone Spongy bone Specialized bone cells Extracellular matrix
  16. 16. 16
  17. 17. 17 Matrix 15% water, 30% collagen, 55% mineral salts Calcium phosphate (hydroxyapatite), calcium carbonate, K, Mg Collagen fiber skeleton = tensile strength Calcification (Mineralization) = hardness
  18. 18. 18
  19. 19. 19 4 Types of Bone Cells Osteogenic cells Osteoblasts Osteocytes Osteoclasts
  20. 20. 20 Osteogenic Cells = Osteoprogenitor cells Undifferentiated Found in periosteum & endosteum Develop into osteoblasts
  21. 21. 21 Osteoblasts Bone-building cells Do not divide Form bone matrix & secrete collagen fibers Develop into osteocytes
  22. 22. 22 Osteocytes Mature bone cells; do not divide Maintain bone tissue No longer secrete matrix
  23. 23. 23
  24. 24. 24 Osteoclasts Largest of the bone cells Originate from fused monocytes (WBC’s) Bone resorption
  25. 25. 25
  26. 26. 26 Compact (Dense) Bone Solid, hard, external layer of bone Forms diaphysis of long bones Resists stresses of weight & movement Arranged in units called osteons
  27. 27. 27 Osteons aka Haversian systems House the osteocytes Abundant vascular tissue: blood vessels & lymphatics Well-innervated with nervous tissue
  28. 28. (a) Osteons (Haversian systems) in compact bone and trabeculae in spongy bone Compact bone Spongy bone Periosteum Medullary cavity Outer circumferential lamellae Interstitial lamellae Concentric lamellae Blood vessels Canaliculi Osteocyte Lacuna Periosteal vein Periosteal artery Periosteum: Outer fibrous layer Inner osteogenic layer Central canal Compact bone Spongy bone Inner circumferential lamellae Trabeculae Medullary cavity See Figure 6.3b for details Perforating canal Perforating (Sharpey’s) fibers Osteon
  29. 29. 29 Osteon Histology Concentric lamellae of matrix around central canal Osteocytes inside lacunae Canaliculi Interstitial lamellae
  30. 30. 30
  31. 31. 31
  32. 32. 32 Spongy Bone No osteons Consists of trabeculae Supports red bone marrow Reduces weight Short, flat, irregular bones Epiphyses of long bones
  33. 33. 33
  34. 34. 34 Blood Supply of Bone Periosteal arteries Nutrient arteries Epiphyseal arteries Metaphyseal arteries
  35. 35. 35 Bone Formation (Ossification) Embryonic CT begins as mesenchyme Template for ossification Intramembranous ossification Endochondral ossification
  36. 36. 36
  37. 37. 37 Intramembranous Ossification Forms flat & irregular bones of skull & mandible “Jelly sandwich” Mesenchyme  Osteogenic cells Ossification center Osteoblasts  Matrix (Calcification) Osteoblasts  Osteocytes Osteogenic cells
  38. 38. 38
  39. 39. 39Osteoblasts
  40. 40. 40 Intramembranous Ossification, cont. Calcifying matrix joins to form trabeculae Spongy bone forms around red bone marrow Surface mesenchyme  Periosteum Superficial spongy bone  Compact bone
  41. 41. 41
  42. 42. Flat bone of skull Mandible Blood capillary Ossification center Mesenchyme Osteoblast Collagen fiber Development of ossification center: osteoblasts secrete organic extracellular matrix 1 Osteocyte in lacuna Calcification: calcium and other mineral salts are deposited and extracellular matrix calcifies (hardens) 2 Canaliculus Osteoblast Newly calcified bone extracellular matrix Mesenchyme condenses Formation of trabeculae: extracellular matrix develops into trabeculae that fuse to form spongy bone 3 Blood vessel Spongy bone trabeculae Osteoblast Periosteum Compact bone tissue Spongy bone tissue Compact bone tissue Development of the periosteum: mesenchyme at the periphery of the bone develops into the periosteum 4
  43. 43. 43 Endochondral Ossification Forms long bones Replaces cartilage with bone Six step process Begins with formation of cartilage model
  44. 44. 44 1. Development of Cartilage Model Originates from mesenchyme Basic shape & length of bone Hyaline cartilage & chondroblasts Perichondrium
  45. 45. 45 2. Growth of Cartilage Model Chondrocytes divide & matrix forms Interstitial growth Appositional growth Mid-region cells burst & lower pH Destroys chondrocytes & triggers calcification
  46. 46. 46 3. Development of Primary Ossification Center Perichondrium  Periosteum Forms periosteal bone collar Nutrient artery penetrates center of bone model Periosteal bud brings osteoblasts & osteoclasts to center
  47. 47. 47
  48. 48. 48 4. Development of Medullary Cavity Osteoblasts deposit matrix over calcified cartilage Form trabeculae of spongy bone Osteoclasts form medullary cavity
  49. 49. 49 5. Development of Secondary Ossification Center Blood vessels enter uncalcified epiphyses Spongy bone develops
  50. 50. 50 6. Formation of Articular Cartilage & Epiphyseal Plate Epiphyseal cartilage does not ossify Remains as articular cartilage Epiphyseal (Growth) plate also remains as cartilage Source of interstitial growth
  51. 51. Development of cartilage model: mesenchymal cells develop into chondroblasts, which form the cartilage model. 1 Proximal epiphysis Diaphysis Distal epiphysis Hyaline cartilage Perichondrium Endochondral Ossification - Overview Growth of cartilage model: growth occurs by cell division of chondrocytes. 2 Uncalcified extracellular matrix Calcified extracellular matrix Nutrient artery Periosteum Primary ossification center Spongy bone Development of primary ossification center: in this region of the diaphysis, bone tissue replaces most of the cartilage. 3
  52. 52. Uncalcified extracellular matrix Development of the medullary (marrow) cavity: bone breakdown by osteoclasts forms the medullary cavity. 4 Calcified extracellular matrix Periosteum Medullary cavity Nutrient artery and vein Development of secondary ossification centers: these occur in the epiphyses of the bone. 5 Secondary ossification center Uncalcified extracellular matrix Epiphyseal artery and vein Articular cartilage Spongy bone Epiphyseal plate Formation of articular cartilage and epiphyseal plate: both structures consist of hyaline cartilage. 6 Endochondral Ossification – Overview, cont.
  53. 53. (b) Twelve-week fetus. The red areas represent bones that are forming (calcified). Clear areas represent cartilage (uncalcified).
  54. 54. 54 Epiphyseal (Growth) Plate Chondrocytes produce cartilage on epiphyseal side Cartilage replaced by bone on diaphyseal side Plate closes at age 18-25 Chondrocytes stop dividing Bone replaces cartilage (epiphyseal line)
  55. 55. 55 4 Zones of Epiphyseal Plate Zone of Resting Cartilage Zone of Proliferating Cartilage Zone of Hypertrophic Cartilage Zone of Calcified Cartilage
  56. 56. Epiphysis (c) Lengthwise growth of bone at epiphyseal plate EPIPHYSEAL (GROWTH) PLATE: Zone of resting cartilage Zone of proliferating cartilage Zone of hypertrophic cartilage Zone of calcified cartilage Diaphysis Articular cartilage New chondrocytes are formed Old chondrocytes are replaced by bone New diaphysi s
  57. 57. 57 Zone of Resting Cartilage Anchors growth plate to bone
  58. 58. 58 Zone of Proliferating Cartilage Rapid cell division (stacks of coins)
  59. 59. 59 Zone of Hypertrophic Cartilage Cells enlarge & remain in columns
  60. 60. 60 Zone of Calcified Cartilage Thin zone – mostly dead cells Osteoblasts & osteoclasts active
  61. 61. 61 Calcified Cartilage
  62. 62. Ridges in periosteum create groove for periosteal blood vessel. 1 Periosteal ridges Periosteum Periosteal blood vessel Perforating canal Groove Periosteal ridges fuse, forming an endosteum-lined tunnel. 2 Endosteum Tunnel Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon. 3 Endosteum Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels. 4 Circumferential lamellae Periosteum New osteon Central (haversian) canal
  63. 63. Ridges in periosteum create groove for periosteal blood vessel. 1 Periosteal ridges Periosteum Periosteal blood vessel Perforating canal Groove
  64. 64. Periosteal ridges fuse, forming an endosteum-lined tunnel. 2 Endosteum Tunnel
  65. 65. Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon. 3 Endosteum
  66. 66. Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels. 4 Circumferential lamellae Periosteum New osteon Central (haversian) canal
  67. 67. Medullary cavity Bone formed by osteoblasts Bone destroyed by osteoclasts Infant Child Young adult Adult (b) Macroscopic changes
  68. 68. 68 Factors Affecting Bone Growth: Nutrition Calcium & Phosphorus Vitamin C  collagen Vitamins K & B12  protein synthesis
  69. 69. 69 Factors Affecting Bone Growth: Hormones Insulinlike Growth Factors (IGFs) Thyroid hormone, Human Growth Hormone (hGH), insulin Estrogen & testosterone
  70. 70. 70 Bone Homeostasis Remodeling Osteoclasts Osteoblasts
  71. 71. 71 Orthodontics
  72. 72. 72 The Effects of Corsetry
  73. 73. 73 Bone Fractures Greenstick Impacted Open Comminuted Pott Colles’ Stress
  74. 74. Ulna Greenstick Radius Wrist bones
  75. 75. Humerus Impacted
  76. 76. Humerus Open (Compound) Radius Ulna
  77. 77. Humerus Comminuted
  78. 78. Tibia Pott Fibula Ankle bones
  79. 79. Ulna Colles’ Radius Wrist bones
  80. 80. 80 Fracture Repair
  81. 81. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Periosteum Fracture hematoma Fibrocartilaginous callus (soft) Reactive phase: formation of fracture hematoma 1 Reparative phase: fibrocartilaginous callus formation 2a Reparative phase: bony callus formation 2b Bone remodeling phase 3 New blood vessel Spongy bone trabeculae Bony (hard) callus Healed fracture
  82. 82. 82 1. Reactive Phase: Formation of fracture hematoma (clot)
  83. 83. 83 2. Reparative Phase: Fibrocartilaginous callus formation
  84. 84. 84 3. Reparative Phase: Bony callus formation
  85. 85. 85 4. Bone Remodeling Phase
  86. 86. 86 Calcium Homeostasis & Bone Tissue Skeleton = Calcium reservoir Nerve & muscle fiber function Blood clotting cascade Enzyme function 9-11 mg Ca+2/100 ml plasma
  87. 87. 87 Hormonal Regulation of Ca+2 Parathyroid Hormone (PTH) (from parathyroid gland) Calcitriol (from kidneys) Calcitonin (from thyroid gland)
  88. 88. STIMULUS CONTROLLED CONDITION Blood calcium (Ca2+) level RECEPTORS CONTROL CENTER Parathyroid hormone gene EFFECTORS RESPONSE Increase in blood Ca2+ level Osteoclasts increase bone resorption Kidneys retain Ca2+ in blood, excrete phosphate in urine, and produce calcitriol Parathyroid gland cells Return to homeostasis when response brings blood Ca2+ level back to normal Disrupts homeostasis by decreasing Detect lowered Ca2+ concentration which increases production of cyclic AMP Input Output Gene “turned on” which increases release of PTH Osteoclasts Kidneys
  89. 89. 89 How do they do this?
  90. 90. 90 Aging & Bone Tissue Demineralization Osteoporosis Reduced protein synthesis Less collagen Fewer growth hormones
  91. 91. 91
  92. 92. 92The End
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