chapter 6. skeletal cartilage chondrocytes in lacunae in jelly- like ground substance ground...
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Chapter 6
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Skeletal CartilageChondrocytes in lacunae in
jelly-like ground substanceGround substance of water &
protein resiliency No blood or nervesPerichondrium3 types
Hyaline cartilageElastic cartilageFibrocartilage
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Cartilage Types
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Cartilage GrowthAppositional growth
Growth from outsideChondroblasts in perichondrium create matrix
on outside of existing cartilageInterstitial growth
Growth from insideChondrocytes create matrix within lacunae
Calcifified cartilage when Ca2+ salts depositedNot bone
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AxialProtection and support
AppendicularLocomotion and
manipulation
Storage and hematopoiesis too
Classifying Bones
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Bone Shape
206 bones (adult)LongShortFlatIrregular
Sesamoid and wormianNot 206
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Bone StructureMarkings (table 6.1)
Projections Grow from bone Attachment for muscles or form joints Tuberosity, crest, trochanter, line, tubercle, epicondyle,
spine, process, head, facet, condyle, ramusDepressions
Conduits for nerves and blood vessels Groove, fissure, foramen, notch, meatus, sinus, fossa
Helps for lab tooTypes
Compact (osteon)Spongy (trabeculae)
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Long Bone AnatomyDiaphysisEpiphyses
Articular surface absorb stressEpiphyseal plate hyaline
MembranesPeriosteum
Outer is dense irregular CT Inner is osseous cells Nutrient foramina Sharpey’s fibers
Endosteum Covers trabeculae Osseous cells
Marrow cavities
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Other Bone Anatomy
Membranes same as long bones
DiploëNo dia- or epiphysisBone marrow, but no cavity
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Composition of Osseous TissueCell types
Osteoprogenitor cellsOsteoblastsOsteocytesOsteoclasts
MatrixOsteoid (organic)
Ground substance and collagen fibers
Structure & strength resist stretching and twisting
Hydroxyapatites (mineral salts) Calcium phosphates Hardness resist compression
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Bone FormationOssification of fetal skeleton around 8 weeks
Intramembranous ossification Flat bones Fibrous membrane is calcified, no cartilage present
Endochondral ossification All other bones Hyaline cartilage templates
GrowthHormonally controlled
hGH, thyroid hormones (T3 and T4), and sex hormonesLength
Interstitial growth at growth platesWidth
Appositional growthRemodeling and repair
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Intramembranous OssificationIncreased vascularization allows mesenchymal
cells to become osteogenic cells osteoblastsOsteoblasts produce osteoid
Trapped osteoblasts become osteocytesOsteoid is calcified by hydroxyapatite
Forms spicules trabeculae around blood vesselsVascularized mesenchyme periosteumOuter trabeculae thicken compact bone
Inner diploë persistRed marrow fills spaces
Fig. 6.8
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Endochondral OssificationChondrocytes hypertrophy
Signals calcification of cartilageChondrocytes die = matrix deteriorates =
lacunae remainChondroblasts continue to divide = lengtheningPeriosteal bud enters cavitites
Perichondrium is vascularized periosteumMesenchyme to osteoblasts
Osseous cells invadeOsteoid produced along hyaline templateOsteoclasts break down spicules, Osteoblasts add osteoid trabeculaeOsteoclasts erode medullary cavity
Process repeats in epiphyses soon after birthNo medullary cavity forms
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Endochondral Ossification
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Epiphyseal (Growth) PlatesResting zone
No bone growth, looks like hyalineProliferative zone
Tall stacks of chondrocytesMitotic division bone lengthens
Hypertrophic zoneChondrocytes enlarge, signal calcify
Calcification/ossification zoneChondrocytes die spicules remainOsteoblasts turn spicules into
trabeculaeOsteoclasts destroy medullary
cavity lengthen
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Thickening of BoneOsteoblasts
Create new osteons on external surface
OsteoclastsBreak down (resorb)
bone on endosteal surface
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Bone Remodeling Antagonistic processes
Bone deposit Bone resorption
(removal)Continuously occurring
Same rates = healthy Disrupted homeostasis =
breaksCa2+ from bone when low
OsteoclastsCa2+ added/redeposited as
needed Osteoblasts
Bone replacement Spongy: 3 – 4 years Compact: about 10 years
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Homeostatic Control of CalciumBlood Ca2+ levels signalParathyroid hormone (PTH)
Osteoclast resorption Only osteoid is safe no salts Mechanical stresses influence
Ca2+ release from bone matrixCalcitonin (negligible)
Inhibits resorptionCa2+ salts deposited into bone
matrix
Vitamins A, C, D, and B12 help
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FracturesTreated by reduction
Closed – physicican setsOpen –pins/wires
Cast immobilizesTypes
Closed (simple)Open (compound)ComminutedCompressionDepressedSpiralEpiphyseal
Smith’sColle’sTransverseImpactedGreenstickPott’s
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Bone RepairHematoma forms kills cells
Inflammatory responseFibrocartilaginous callus
Phagocytes & osteoclasts clean debris
Fibroblasts & chondrocytes lay down collagen and cartilage to connect
Osteoblasts lay down spongy bone
Excess bone on exterior and in cavity removed
Compact bone recreates shaft
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Bone DisordersOsteomalacia (rickets): inadequate mineralization of
boneOsteoporosis: bone resporption faster than depositSpina bifida: incomplete closure of vertebraeAchondroplasia: dwarfism; defective cartilage growth
and improper endochondral ossificationAcromegaly: gigantism; growth plate slow to ossifyScoliosis: lateral curve of spineKyphosis: hunckback spine; exaggerated thoracic
curvatureLordosis: swayback; exaggerated lumbar curvatureCleft palate: palatine bones don’t fuseCarpal tunnel syndrome: nerve impairment in wrist