Chapter 6

Skeletal CartilageChondrocytes in lacunae in

jelly-like ground substanceGround substance of water &

protein resiliency No blood or nervesPerichondrium3 types

Hyaline cartilageElastic cartilageFibrocartilage

Cartilage Types

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

AxialProtection and support

AppendicularLocomotion and

manipulation

Storage and hematopoiesis too

Classifying Bones

Bone Shape

206 bones (adult)LongShortFlatIrregular

Sesamoid and wormianNot 206

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)

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

Other Bone Anatomy

Membranes same as long bones

DiploëNo dia- or epiphysisBone marrow, but no cavity

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

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

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

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

Endochondral Ossification

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

Thickening of BoneOsteoblasts

Create new osteons on external surface

OsteoclastsBreak down (resorb)

bone on endosteal surface

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

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

FracturesTreated by reduction

Closed – physicican setsOpen –pins/wires

Cast immobilizesTypes

Closed (simple)Open (compound)ComminutedCompressionDepressedSpiralEpiphyseal

Smith’sColle’sTransverseImpactedGreenstickPott’s

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

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