BONE
 BONE
Functions of Bone
• Supports soft tissue
• Protects vital organs (cranium, thoracic
  cavity)
• Contains bone marrow
• Res...
Specialized CT
• Cells
  – Osteoblasts
  – Osteocytes
  – Osteoclasts
• Bone matrix
  – Calcified material,
    lacunae
• ...
Anatomy of a L ong Bone
Osteoblasts
• Synthesize organic components of matrix
  (collagen type I, proteoglycans,
  glycoproteins.)
• Collagen form...
Osteoblasts
Osteocytes
• Mature bone cells that sit in lacunae
• Gap junctions between osteocytes provide
  nutrition (15 cells in a r...
Osteocyte with Cytoplasmic E xtensions
Osteocytes with Canaliculi
Photomicrograph of dried
bone ground very thin.

The lacunae and
canaliculi filled with air
def...
Osteoclasts
•   Derived from monocytes; engulf bony material
•    Active osteoblasts stimulate osteoclast activity
•   L a...
Osteoclasts
Bone Resorption
On this image,
                       Remodeling
the deepest red
color is bone
while pink
represents
either
fibrocartilage...
Bone Replacing Cartilage
Remodeling Bone
E ndochondral Ossification
Photomicrograph of endochondral
ossification. In the upper region is
a row of osteoblasts with ...
Osteon
• L ong cylinder parallel
  to long axis of
  diaphysis
• Consists of:
  – Haversian canal with
    nerves, blood v...
Compact Bone
Canaliculi between Osteocytes
Bone Tissue: Supportive Connective Tissue
             E xtracellular Matrix
25% Water
25% Protein or organic matrix
    9...
Two K inds of Bone
Compact Bone

Spongy Bone
Compact Bone
• Compact bone is arranged in units called osteons or
  Haversian systems.

• Osteons (Haversian canal) conta...
Compact bone
       - arranged into concentric rings called Haversian systems
       - provides strength
       - is exter...
Histology of Bone Tissue
Histology of Compact Bone
• Osteon is concentric rings (lamellae) of calcified matrix
  surrounding a vertically oriented ...
Compact Bone
The Trabeculae of Spongy Bone
• L attice work of thin plates of bone called trabeculae oriented
  along lines of stress
• ...
Spongy Bone
• Spongy (cancellous) bone does
  not contain osteons.
• It     consists  of     trabeculae
  surrounding many...
BONE FORMATION
• All embryonic connective tissue begins as mesenchyme.
• Bone formation is termed osteogenesis or ossifica...
Two K inds of
  Ossification
1. Intramembranous
    Ossification



2. E ndochondral
   Ossification
Intramembranous Ossification
Also called dermal ossification because it
normally occurs in the deeper layers of
connective...
Intramembranous Ossification
Centers of Ossification
Centers of Ossification
E ndochondral Ossification


Developing bones are deposited as a hyaline
cartilage model and then this cartilage is
replac...
E ndochondral Ossification
E ndochondral Ossification
Growth at epiphyseal
  plates
Zones of epiphyseal plates

Zone of Resting Cartilage
Zone of Proliferating Cartilage
Zone o...
• Zone of resting cartilage                Zones of Growth in
   – anchors growth plate to bone           E piphyseal Plat...
Growth at epiphyseal plates

Zones of epiphyseal plates


Zone of Resting Cartilage
Zone of Proliferating
Cartilage
Zone o...
Growth in Thickness
• Bone can grow in thickness or diameter only by
  appositional growth.
• The steps in these process a...
Bone Growth in Width




• Only by appositional growth at the bone’s surface
• Periosteal cells differentiate into osteobl...
Calcium homeostasis
Factors That Affect Bone Growth
1.   Minerals
2.   Vitamins
3.   Hormones
4.   E xercise
Factors That Affect Bone Growth
                 Minerals
Calcium      Makes bone matrix hard
             Hypocalcemia: l...
Factors That Affect Bone Growth
                    Vitamins
Vitamin A     Controls activity, distribution, and
          ...
Factors That Affect Bone Growth
                       Hormones
Human Growth Hormone Promotes general growth of all
      ...
Bone
Fractures
Terms:
Closed/Open
Partial/Complete
Displaced/Non-displaced
Simple/Compound

Other Fractures:
Spiral
Transv...
Subluxation : an incomplete or
partial dislocation of a joint or organ.


L uxation: a complete dislocation of
A joint or ...
Bone Fracture Repair
Steps in Fracture Repair

1. Formation of a fracture hematoma

Immediately after the fracture, there is
a sharp fracture l...
Steps in Fracture Repair


 2. Fibrocartilaginous Callus
    Formation

At 2 weeks there is much visible callus.
There is ...
Bone Fracture Repair
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Bones

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  1. 1. BONE BONE
  2. 2. Functions of Bone • Supports soft tissue • Protects vital organs (cranium, thoracic cavity) • Contains bone marrow • Reservoir of Ca++, PO4 to maintain constant concentrations in body fluids • Allows body to move
  3. 3. Specialized CT • Cells – Osteoblasts – Osteocytes – Osteoclasts • Bone matrix – Calcified material, lacunae • And more… . – Canaliculi – Periosteum – E ndosteum
  4. 4. Anatomy of a L ong Bone
  5. 5. Osteoblasts • Synthesize organic components of matrix (collagen type I, proteoglycans, glycoproteins.) • Collagen forms osteoids: strands of spiral fibers that form matrix • Influence deposit of Ca++, PO4. • Active vs inactive osteoblasts • E strogen, PTH stimulate activity Parathyroid hormone (PTH),
  6. 6. Osteoblasts
  7. 7. Osteocytes • Mature bone cells that sit in lacunae • Gap junctions between osteocytes provide nutrition (15 cells in a row) • Maintain bony matrix; long lived cells • Stimulated by calcitonin; inhibited by PTH
  8. 8. Osteocyte with Cytoplasmic E xtensions
  9. 9. Osteocytes with Canaliculi Photomicrograph of dried bone ground very thin. The lacunae and canaliculi filled with air deflect the light and appear dark, showing the communication between these structures through which nutrients derived from blood vessels flow.
  10. 10. Osteoclasts • Derived from monocytes; engulf bony material • Active osteoblasts stimulate osteoclast activity • L arge, branched, motile cells • Secrete enzymes that digest matrix
  11. 11. Osteoclasts
  12. 12. Bone Resorption
  13. 13. On this image, Remodeling the deepest red color is bone while pink represents either fibrocartilage (i.e., collagen within cartilage) or mineralized cartilage. The central clearing represents the invasion of bone into calcified cartilage. Osteoblast are laying down new bone toward the left of the upper boundary of this cavity. Ostoblasts are removing previously-formed bone .
  14. 14. Bone Replacing Cartilage
  15. 15. Remodeling Bone
  16. 16. E ndochondral Ossification Photomicrograph of endochondral ossification. In the upper region is a row of osteoblasts with intense cytoplasmic basophilia, a feature to be expected in cells synthesizing a glycoprotein (collagen). Note an osteoblast being captured in the bone matrix (arrow). Between the layer of osteoblasts and the calcified bone matrix is a pale region made of noncalcified bone matrix called Osteoid.
  17. 17. Osteon • L ong cylinder parallel to long axis of diaphysis • Consists of: – Haversian canal with nerves, blood vessels; lamellae with osteocytes • Haversian canals communicate with marrow cavity, periosteum, other canals through V olkmann’ s canals
  18. 18. Compact Bone
  19. 19. Canaliculi between Osteocytes
  20. 20. Bone Tissue: Supportive Connective Tissue E xtracellular Matrix 25% Water 25% Protein or organic matrix 95% Collagen Fibers 5% Chondroitin Sulfate 50% Crystalized Mineral Salts Hydroxyapatite (Calcium Phosphate) Other substances: L ead, Gold, Strontium, Plutonium, etc.
  21. 21. Two K inds of Bone Compact Bone Spongy Bone
  22. 22. Compact Bone • Compact bone is arranged in units called osteons or Haversian systems. • Osteons (Haversian canal) contain blood vessels, lymphatic vessels, nerves • Surrounding this canal are concentric rings of osteocytes along with the calcified matrix. • Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.
  23. 23. Compact bone - arranged into concentric rings called Haversian systems - provides strength - is external & solid - Haversian system consists of: lamella - concentric ring of matrix lacuna - openings between lamellae for osteocytes osteocytes - mature bone cell Haversian canal - in center of lamella; houses vessels Canaliculi - radiating channels between lacuna and Haversian canal for nutrients and wastes Volkmann canal - crosswise canals from Haversian canal to exterior containing blood vessels and nerves
  24. 24. Histology of Bone Tissue
  25. 25. Histology of Compact Bone • Osteon is concentric rings (lamellae) of calcified matrix surrounding a vertically oriented blood vessel • Osteocytes are found in spaces called lacunae • Osteocytes communicate through canaliculi filled with extracellular fluid that connect one cell to the next cell • Interstitial lamellae represent older osteons that have been partially removed during tissue remodeling
  26. 26. Compact Bone
  27. 27. The Trabeculae of Spongy Bone • L attice work of thin plates of bone called trabeculae oriented along lines of stress • Spaces in between these struts are filled with red marrow where blood cells develop • Found in ends of long bones and inside flat bones such as the hipbones, sternum, sides of skull, and ribs. No true Osteons.
  28. 28. Spongy Bone • Spongy (cancellous) bone does not contain osteons. • It consists of trabeculae surrounding many red marrow filled spaces. • It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones. • Spongy bone tissue is light and supports and protects the red bone marrow. Spongy bone - irregular lattice work of bone called trabecula - spaces filled with red bone marrow - osteocytes trapped within calcium matrix
  29. 29. BONE FORMATION • All embryonic connective tissue begins as mesenchyme. • Bone formation is termed osteogenesis or ossification and begins when mesenchymal cells provide the template for subsequent ossification. • Two types of ossification occur. – Intramembranous ossification is the formation of bone directly from or within fibrous connective tissue membranes. – E ndochondrial ossification is the formation of bone from hyaline cartilage models.
  30. 30. Two K inds of Ossification 1. Intramembranous Ossification 2. E ndochondral Ossification
  31. 31. Intramembranous Ossification Also called dermal ossification because it normally occurs in the deeper layers of connective tissue of the dermis of the skin. • All roofing bones of the Skull Frontal bone Parietal bones Occipital bone Temporal bones • Mandible • Clavicle
  32. 32. Intramembranous Ossification
  33. 33. Centers of Ossification Centers of Ossification
  34. 34. E ndochondral Ossification Developing bones are deposited as a hyaline cartilage model and then this cartilage is replaced by bone tissue. All bones of the body except: • All roofing bones of the Skull • Mandible • Clavicle
  35. 35. E ndochondral Ossification
  36. 36. E ndochondral Ossification
  37. 37. Growth at epiphyseal plates Zones of epiphyseal plates Zone of Resting Cartilage Zone of Proliferating Cartilage Zone of Hypertrophic Cartilage Zone of Calcified Cartilage
  38. 38. • Zone of resting cartilage Zones of Growth in – anchors growth plate to bone E piphyseal Plate • Zone of proliferating cartilage – rapid cell division (stacked coins) • Zone of hypertrophic cartilage – cells enlarged & remain in columns • Zone of calcified cartilage – thin zone, cells mostly dead since matrix calcified – osteoclasts removing matrix – osteoblasts & capillaries move in to create bone over calcified cartilage
  39. 39. Growth at epiphyseal plates Zones of epiphyseal plates Zone of Resting Cartilage Zone of Proliferating Cartilage Zone of Hypertrophic Cartilage Zone of Calcified Cartilage
  40. 40. Growth in Thickness • Bone can grow in thickness or diameter only by appositional growth. • The steps in these process are: – Periosteal cells differentiate into osteoblasts which secrete collagen fibers and organic molecules to form the matrix. – Ridges fuse and the periosteum becomes the endosteum. – New concentric lamellae are formed. – Osetoblasts under the peritsteum form new circumferential lamellae.
  41. 41. Bone Growth in Width • Only by appositional growth at the bone’s surface • Periosteal cells differentiate into osteoblasts and form bony ridges and then a tunnel around periosteal blood vessel. • C oncentric lamellae fill in the tunnel to form an osteon.
  42. 42. Calcium homeostasis
  43. 43. Factors That Affect Bone Growth 1. Minerals 2. Vitamins 3. Hormones 4. E xercise
  44. 44. Factors That Affect Bone Growth Minerals Calcium Makes bone matrix hard Hypocalcemia: low blood calcium levels. Hypercalcemia: high blood calcium levels. Phosphorus Makes bone matrix hard Magnesium Deficiency inhibits osteoblasts Boron May inhibit calcium loss, increase levels of estrogens Manganese Inhibits formation of new bone tissue
  45. 45. Factors That Affect Bone Growth Vitamins Vitamin A Controls activity, distribution, and coordination of osteoblasts/osteoclasts Vitamin B12 May inhibit osteoblast activity Vitamin C Helps maintain bone matrix, deficiency leads to decreased collagen production which inhibits bone growth and repair (scury) disorder due to a lack of Vitamin C Vitamin D (Calcitriol) Helps build bone by increasing calcium absorption. Deficiencies result in “Rickets” in children
  46. 46. Factors That Affect Bone Growth Hormones Human Growth Hormone Promotes general growth of all body tissue and normal growth in children Insulin-like Growth Factor Stimulates uptake of amino acids and protein synthesis Insulin Promotes normal bone growth and maturity Thyroid Hormones Promotes normal bone growth and maturity E strogen and Increases osteogenesis at puberty Testosterone and is responsible for gender differences of skeletons
  47. 47. Bone Fractures Terms: Closed/Open Partial/Complete Displaced/Non-displaced Simple/Compound Other Fractures: Spiral Transverse L ongitudinal Pathologic
  48. 48. Subluxation : an incomplete or partial dislocation of a joint or organ. L uxation: a complete dislocation of A joint or organ.
  49. 49. Bone Fracture Repair
  50. 50. Steps in Fracture Repair 1. Formation of a fracture hematoma Immediately after the fracture, there is a sharp fracture line with associated soft tissue swelling. At the fracture Site, there is abundant hematoma with beginning fibroblastic penetration.
  51. 51. Steps in Fracture Repair 2. Fibrocartilaginous Callus Formation At 2 weeks there is much visible callus. There is also bone resorption and osteoporosis, both difficult to see in this case because of the overlying callus. There has been migration of chondroblasts into the area and cartilage is beginning to cover the ends of the fracture. New osteous tissue is produced enchondrally.
  52. 52. Bone Fracture Repair

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