Bone Growth and Development

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enger91
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83856
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Bone Growth and Development
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2011-05-05 00:41:46
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bone formation animal growth development
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University of MN Spring 2011
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  1. Dense connective tissue
    • many fibers aligned parallel to eachother
    • strong, little flexibility
    • relatively few cells, non-vascular
  2. Loose connective tissue
    • few fibers, aligned randomly
    • highly porous
    • flexible
    • relatively few cells, non-vascular
  3. Cartilage
    • strength and flexibility varies with type and abundance if fibers
    • relatively few cells
    • fibers aligned randomly
    • non-vascular
  4. Periosteum
    • a connective tissue sheath made up of a double layer of cells surrounding the bone
    • loosely adheared when growing, tightly adhered when no longer growing
  5. Functions of the periosteum
    • bridge between the bone and other connective tissues
    • proliferation
    • nutrition
    • source of osteogenic precursor cells (very inside layer)
    • some growth restriction properties
  6. Endosetum
    connective tissue sheath made up of a single layer of cells which lines the inner surface of the bone
  7. Functions of the endosetum
    • nutrition
    • sources of osteogenic precursor cells
  8. Bone
    • highly specialized form of connective tissue
    • very hard; somewhat flexible, able to withstand stress
    • dynamic tissue -10% of bone is replaced every year
    • exhibits regenerative powers
  9. Function of bone
    • support
    • protection
    • contains bone marrow
    • maintains mineral homeostasis
    • locomotion
  10. Factors influencing bone mass
    • physical activity
    • dietary calcium
    • heredity
    • oral contreaceptives
    • age
  11. Composition of bone
    • 20% water
    • 45-50% inorganic matterial
    • 30-35% organic matter; 90-95% collagen
  12. Compact bone
    • aka cortical
    • covers the surface of all bones
    • dense
    • very strong
    • no cavities
    • Haversian system
    • collagen fibers arranged in parallel to eachother in helical formation but perpendicular to the next lamella; gives strength to bone
  13. Haversian canal
    • central canal where blood vessels and nerves are contained
    • lined with endosteum
    • younger canals are larger (due to inward growth)
  14. Cancellous bone
    • aka spongy, trabecular
    • consists of a network of fine, interlacing trabeculae
    • has areas with numerous interconnecting cavities
    • typically surrounded by cortical bone
    • bone marrow is located in the spaces between the trabeculae
    • organization is dependent on the mechanical stress put on the bone
    • able to withstand less stress then cortical bone
    • Lamelia: layers of calcium deposits surrounding osteocytes
    • Osteocytes: bone cells
    • Lacuna: space where osteocytes reside
    • Canaliculus: small canals connecting lacuna and osteocytes
  15. Osteoporosis
    • aka porus bone
    • characterised by low bone mass and structural deterioration
    • bone fragility and increased susceptibility to fractures
  16. Types of bone cells (5)
    • Osteoprogenitor cells: source of new cells
    • Osteoblasts: builders of bone
    • Osteocytes: housekeepers of bone (in lacunea)
    • Bone lining cells: surface protection
    • Osteoclasts: bone demolition
  17. Osteoprogenitor cells
    • source of new bone cells
    • located in periosteum and endosteum
    • proliferation and renewal (numbers decrease with age)
    • differentiate sequentially into osteoblasts, osteocytes, and bone lining cells
  18. Osteoblasts
    • responsible for the formation of new bone: 1. synthesize the organic matrix of the bone 2. regulate the mineralization of bone
    • secrete osteoid in one direction (toward an existing hard surface)
    • cuboidal cell
    • one-cell thick layer loacted exclusively at the surface of bone (interior and exterior)
    • don't proliferate
    • Communicates with other osteoblasts, osteocytes, osteoclasts, and non-bone cells
    • respond to growth factors and hormones from other cells
    • capable of synthesizing growth factors
  19. Osteocytes
    • house keepers
    • osteoblasts that have become trapped in the mineralized matrix of bone (differentiate into osteoclast)
    • most abundant type of cell in mature bone
    • maintain mineralized matrix
    • involved in the exchange of mineral ions between matrix and extracellular fluid
    • detection of strain (through changes in electrical current)
  20. Bone lining cells
    • not a part of the periosteum (just underneath)
    • thin, flat cells covering most bone surfaces in adult bone (surfaces not undergoing formaion or reabsorption)
    • serve as a selective barrier
    • When remodeling is required: secrete collagenase, which removes unmineralized collagen, allowing for osteoclast attachment
  21. Where are osteocytes located?
    • Within the lacunae
    • in contact with each other through canaliculi
  22. What is bone adaptation dependent on?
    • strain magnitude
    • duration
    • frequency
    • history type (i.e. compression, tension, shear)
    • distribution
  23. Osteoclasts
    • demolition cells
    • arise from a different type of cell than the rest of the bone cells
    • travel to bone via the bloodstream
    • differentiate and fuse to form osteoclasts
    • large, multinucleated cells w/a ruffled border
    • must sit on a mineralized matrix
    • reabsorb the mineralized matrix of the bone
    • erode bone with enzymes and acid
    • create pits which lead to a new Haversian canal
  24. Calcitonin
    • secreted when blood Ca levels are high
    • acts directly on osteoclasts -inhibiting bone reaborption
    • increases renal excretion of Ca and P
  25. Parathyroid Hormone (PTH)
    • secreted when blood Ca levels are low
    • increases intestinal Ca aborption
    • Mobilizes Ca and P from bone
    • increases active vitamin D in kidney to decrease P
    • maxamizes reaborpion of Ca by kidney
    • increase number and activity of osteoclasts
  26. What are the 2 methods of bone remodeling?
    intramembraneous and endochondral
  27. Intramembranous bone formation
    • Transformation of soft connective tissue into bone
    • Mesenchymal cells become closely packed within a soft connective tissue layer
    • Cells differentiate into osteoblasts at a number of different sites simltaneously
    • Osteoblasts at each site make new bone
    • Ossification centers (sites of new bone) merge together
    • Areas of assification spread out toward each other and eventualy meet
  28. Endochondral
    replacement of cartilage with bone
  29. Fontanelles
    • aka soft spots
    • regions where the connective tissue has not been ossified
  30. Endochondral bone formation
    • replacement of cartilage with bone
    • bone collar growth (bone collar formation = intramembranous)
  31. Cartilage
    specilized form of connective tissue
  32. 3 types of cells present in cartilage
    • Chondrocytes: house keeping cells -located within the cartilage matrix
    • Chondroblasts: builders of cartilage
    • Chondroclasts: demolition of cartilage
  33. 2 ways cartilage grows
    • on the surface by the recruitment of chondroblasts
    • interstitially by proliferation of the chondrocytes which separate and continue to synthesize matrix
  34. Perichondrium
    connective tissue sheath which surrounds cartilage
  35. 2 processes of endochondral bone formation
    • hypertrophy and calcification of cartilage model
    • osteogenic bud penetration into spaces left by degenerating cartilage model bring in osteoblasts to form bone
  36. Primary ossification of diaphysis
    • mesenchymal cells condense/secrete substances forming a cartilage model
    • perichondrium (connective tissue sheath around the cartilage model) is formed
    • intramembranous ossification of the inner layer of perichondrium occurs forming a bone collar around thediaphysis shaft of the cartilage model; (should completion of the ossification fail to take place, cartilage growsbetween the defect to produce an exostosis; the perichondrium of the shaft develops osteogenic potential andassumes the role of the periosteum.
    • by definition the perichondrium is now a periosteum
    • diffusion of nutrients are blocked by the bone collar – resulting in starvation/death of the chondrocytes
    • the chondrocytes of the cartilage model begin to enlarge greatly: they swell through a process of fluid intake;they reabsorb their surrounding matrix, causing an enlargement of the lacunas; The intercellular substancebetween the swollen cells then decreases, leaving only slender perforated trabeculae of cartilage matrix; thechondrocytes lose their ability to maintain the surrounding matrix, calcium deposits form and the cartilage thatis left becomes calcified.
    • the chondrocytes degenerate and leave large interconnecting spaces
    • osteoclasts from the periosteum on the bone collar erode holes in the bone collar, through which bloodvessels and osteogenic precursor cells (from the periosteum; the periosteum is highly heterogeneous andcontains cells in all transitional stages of osteogenic differentiation,) arrive (forming an osteogenic bud)
    • osteogenic precursor cells penetrate the calcified cartilage matrix, proliferate and give rise to osteoblasts andbone marrow cells
    • chondroclasts resorb calcified cartilage
    • osteoblasts deposit osteoid on the calcified cartilage remnants; osteoid becomes ossified: primary bonedevelops
    • osteoclasts and osteoblasts remodel the interior of the bone
  37. Secondary ossification of epiphysis
    • occurs at the end of the bone (radial expansion)
    • found in epiphysis (has no perichondrium)
    • osteogenesis begins at specific sites and coalexce into an ossification center
  38. Generalities of bone formation
    • primary ossification center occurs first
    • secondary ossification center occurs second
    • distal portion of the long bone contributes 60% of the total length whereas proximal portion contributes 40%
  39. What are the 5 zones of epiphyseal plate growth starting from epiphysis?
    • Resting: or reserve zone -chondrocyte stem cells
    • Proliferative zone: chondrocytes increase in number in stacks
    • Hypertrophic zone: chondrocytes increase in size, surrounding cartilage becones calcified
    • Degenerative zone: chondrocytes undergo apoptosis, the cartilage becomes calcified and forms the scaffolding for osteoblasts
    • Ossification zone: endochondral bone tissue is formed by osteoblasts brought by the encroaching diaphyseal marrow tissue
    • A) resting
    • B) proliferative
    • C) proliferative
    • D) hypertrophic
    • E) bone formation
  40. Cellular activities that affect long bone growth (3)
    • the rate of division of the chondrocytes
    • the size of the proliferation zone
    • the degree of cellular hypertrophy
  41. Factors that affect bone growth
    • Systemic factors: genetics, nutrition, hormones, etc
    • Local factors: physical stress, blood supply, mineralization of osteoid
  42. GH/IGF impact on bone
    • increased osteoblast proliferation
    • increase osteoblast differentiation
  43. Primary bone
    • immature
    • collagen is randomly oriented
    • less mineral
    • fewer osteocytes
    • temporary (replaced by secondary bone in adult or after repair)
  44. Secondary bone
    • mature bone
    • lamellar configuration
    • trabeculae
    • Haversian
    • more mineral
    • more osteocytes
  45. Medical intervention for a bone break
    • reduction (bring bone pieces together)
    • fixation
    • use
  46. 3 phases of bone healing
    • Inflammatory: immune system respince to injury
    • Reparitive: repairs typically exceed original size
    • Remodeling: functional adaptation
  47. Inflammatory phase
    • blood vessels associated with the Haversian system are damaged
    • periosteum is often torn
    • soft tissue is often damaged
    • a hematoma forms within the bone and beneath the periosteum
    • osteocytes die
  48. Reparitive phase
    • callus forms: mass of new bone forming around the periphery of fracture
    • no callus formed under condition of compression and rigid-fixation
  49. What is callus formation dependent on?
    • fracture fragments
    • movement between fragments
  50. Remodeling phase
    • removal of bone from a site
    • addition of bone to a site
    • facilitated by motion of adjacent joints and use of extremity
    • final bone will closely resemble the original structure

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