1 Chapter 6 The Skeletal System:Bone Tissue Dynamic and ever-changing throughout life Dynamic and ever-changing throughout life Skeleton composed of many.

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Chapter 6Chapter 6The Skeletal System:Bone The Skeletal System:Bone

TissueTissue

Dynamic and ever-changing throughout lifeDynamic and ever-changing throughout life Skeleton composed of many different tissuesSkeleton composed of many different tissues

• cartilage, bone tissue, epithelium, nerve, blood cartilage, bone tissue, epithelium, nerve, blood forming tissue, adipose, and dense connective forming tissue, adipose, and dense connective tissuetissue

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Functions of BoneFunctions of Bone Supporting & protecting soft tissuesSupporting & protecting soft tissues Attachment site for muscles Attachment site for muscles

making movement possiblemaking movement possible Storage of the minerals, calcium & Storage of the minerals, calcium &

phosphate -- mineral homeostasis phosphate -- mineral homeostasis Blood cell production occurs in red Blood cell production occurs in red

bone marrow (hemopoiesis)bone marrow (hemopoiesis) Energy storage in yellow bone Energy storage in yellow bone

marrowmarrow

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Anatomy of a Long BoneAnatomy of a Long Bone Diaphysis = shaftDiaphysis = shaft Epiphysis = one end of a long boneEpiphysis = one end of a long bone Metaphysis = growth plate regionMetaphysis = growth plate region Articular cartilage over joint surfaces Articular cartilage over joint surfaces

acts as friction & shock absorberacts as friction & shock absorber Medullary cavity = marrow cavityMedullary cavity = marrow cavity Endosteum = lining of marrow cavityEndosteum = lining of marrow cavity Periosteum = tough membrane Periosteum = tough membrane

covering bone but not the cartilage covering bone but not the cartilage • fibrous layer = dense irregular CTfibrous layer = dense irregular CT• osteogenic layer = bone cells & blood osteogenic layer = bone cells & blood

vessels that nourish or help with repairsvessels that nourish or help with repairs

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Histology of BoneHistology of Bone

A type of connective A type of connective tissue as seen by tissue as seen by widely spaced cells widely spaced cells separated by matrixseparated by matrix

Matrix of 25% water, Matrix of 25% water, 25% collagen fibers 25% collagen fibers & 50% crystalized & 50% crystalized mineral saltsmineral salts

4 types of cells in 4 types of cells in bone tissuebone tissue

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Cell Types of BoneCell Types of Bone

Osteoprogenitor cells ---- undifferentiated cells Osteoprogenitor cells ---- undifferentiated cells • can divide to replace themselves & can become osteoblastscan divide to replace themselves & can become osteoblasts• found in inner layer of periosteum and endosteumfound in inner layer of periosteum and endosteum

Osteoblasts--form matrix & collagen fibers but can’t divideOsteoblasts--form matrix & collagen fibers but can’t divide Osteocytes ---mature cells that no longer secrete matrixOsteocytes ---mature cells that no longer secrete matrix Osteoclasts---- huge cells from fused monocytes (WBC)Osteoclasts---- huge cells from fused monocytes (WBC)

• function in bone resorption at surfaces such as endosteumfunction in bone resorption at surfaces such as endosteum

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Matrix of BoneMatrix of Bone Inorganic mineral salts provide bone’s Inorganic mineral salts provide bone’s

hardnesshardness Organic collagen fibers provide bone’s Organic collagen fibers provide bone’s

flexibilityflexibility• their tensile strength resists being stretched or their tensile strength resists being stretched or

torntorn Mineralization (calcification) is hardening of Mineralization (calcification) is hardening of

tissue when mineral crystals deposit around tissue when mineral crystals deposit around collagen fiberscollagen fibers

Bone is not completely solid since it has small Bone is not completely solid since it has small spaces for vessels and red bone marrowspaces for vessels and red bone marrow• spongy bone has many such spacesspongy bone has many such spaces• compact bone has very fewcompact bone has very few

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Compact or Dense BoneCompact or Dense Bone

Looks like solid hard Looks like solid hard layer of bonelayer of bone

Makes up the shaft of Makes up the shaft of long bones and the long bones and the external layer of all external layer of all bones bones

Resists stresses Resists stresses produced by weight and produced by weight and movementmovement

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Histology of Compact BoneHistology of Compact Bone Osteon is concentric rings (lamellae) of calcified Osteon is concentric rings (lamellae) of calcified

matrix surrounding a vertically oriented blood matrix surrounding a vertically oriented blood vessel vessel

Osteocytes found in spaces called lacunaeOsteocytes found in spaces called lacunae Osteocytes communicate through canaliculi filled Osteocytes communicate through canaliculi filled

with extracellular fluid that connect one cell to with extracellular fluid that connect one cell to the next cellthe next cell

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The Trabeculae of Spongy The Trabeculae of Spongy Bone Bone

Latticework of thin plates of bone called trabeculae Latticework of thin plates of bone called trabeculae oriented along lines of stressoriented along lines of stress

Spaces in between these struts are filled with red Spaces in between these struts are filled with red marrow where blood cells developmarrow where blood cells develop

Found in ends of long bones and inside flat bones such Found in ends of long bones and inside flat bones such as the hipbones, sternum, sides of skull, and ribs.as the hipbones, sternum, sides of skull, and ribs.

No true Osteons.

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Bone ScanBone Scan

Radioactive tracer is given intravenouslyRadioactive tracer is given intravenously Amount of uptake is related to amount of Amount of uptake is related to amount of

blood flow to the boneblood flow to the bone ““Hot spots” are areas of increased Hot spots” are areas of increased

metabolic activity that may indicate metabolic activity that may indicate cancer, abnormal healing or growthcancer, abnormal healing or growth

““Cold spots” indicate decreased Cold spots” indicate decreased metabolism of decalcified bone, fracture metabolism of decalcified bone, fracture or bone infectionor bone infection

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Blood and Nerve Supply of Blood and Nerve Supply of BoneBone

Periosteal arteriesPeriosteal arteries• supply periosteumsupply periosteum

Nutrient arteriesNutrient arteries• enter through nutrient enter through nutrient

foramenforamen• supplies compact bone of supplies compact bone of

diaphysis & red marrowdiaphysis & red marrow Metaphyseal & epiphyseal Metaphyseal & epiphyseal

aa. aa. • supply red marrow & bone supply red marrow & bone

tissue of epiphysestissue of epiphyses

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Bone Formation or Bone Formation or OssificationOssification

All embryonic connective tissue begins All embryonic connective tissue begins as mesenchyme.as mesenchyme.

Intramembranous bone formation = Intramembranous bone formation = formation of bone directly from formation of bone directly from mesenchymal cells.mesenchymal cells.

Endochondral ossification = formation Endochondral ossification = formation of bone within hyaline cartilage.of bone within hyaline cartilage.

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Intramembranous Bone Intramembranous Bone FormationFormation

Mesenchymal cells become osteoprogenitor cells then osteoblasts.Mesenchymal cells become osteoprogenitor cells then osteoblasts. Osteoblasts surround themselves with matrix to become osteocytes.Osteoblasts surround themselves with matrix to become osteocytes. Matrix calcifies into trabeculae with spaces holding red bone marrow.Matrix calcifies into trabeculae with spaces holding red bone marrow. Mesenchyme condenses as periosteum at the bone surface.Mesenchyme condenses as periosteum at the bone surface. Superficial layers of spongy bone are replaced with compact bone.Superficial layers of spongy bone are replaced with compact bone.

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Endochondral Bone Formation Endochondral Bone Formation (1)(1)

Development of Cartilage Development of Cartilage modelmodel• Mesenchymal cells form a Mesenchymal cells form a

cartilage model of the bone cartilage model of the bone during developmentduring development

Growth of Cartilage modelGrowth of Cartilage model• in length by chondrocyte cell in length by chondrocyte cell

division and matrix formation ( division and matrix formation ( interstitial growth)interstitial growth)

• in width by formation of new in width by formation of new matrix on the periphery by matrix on the periphery by new chondroblasts from the new chondroblasts from the perichondrium (appositional perichondrium (appositional growth)growth)

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Endochondral Bone Formation (2)Endochondral Bone Formation (2)

Development of Primary Development of Primary Ossification CenterOssification Center• nutrient artery penetrates center nutrient artery penetrates center

of cartilage modelof cartilage model• osteoblasts deposit bone matrix osteoblasts deposit bone matrix

over calcified cartilage forming over calcified cartilage forming spongy bone trabeculaespongy bone trabeculae

• osteoclasts form medullary cavityosteoclasts form medullary cavity

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Endochondral Bone Formation (3)Endochondral Bone Formation (3)

Development of Secondary Ossification CenterDevelopment of Secondary Ossification Center• blood vessels enter the epiphyses around time of birthblood vessels enter the epiphyses around time of birth• spongy bone is formed but no medullary cavityspongy bone is formed but no medullary cavity

Formation of Articular CartilageFormation of Articular Cartilage• cartilage on ends of bone remains as articular cartilage.cartilage on ends of bone remains as articular cartilage.

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Bone Growth in LengthBone Growth in Length Epiphyseal plate or cartilage Epiphyseal plate or cartilage

growth plategrowth plate• cartilage cells are produced by cartilage cells are produced by

mitosis on epiphyseal side of platemitosis on epiphyseal side of plate• cartilage cells are destroyed and cartilage cells are destroyed and

replaced by bone on diaphyseal replaced by bone on diaphyseal side of plateside of plate

Between ages 18 to 25, Between ages 18 to 25, epiphyseal plates close.epiphyseal plates close.• cartilage cells stop dividing and cartilage cells stop dividing and

bone replaces the cartilage bone replaces the cartilage (epiphyseal line)(epiphyseal line)

Growth in length stops at age 25Growth in length stops at age 25

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Zones of Growth in Epiphyseal Zones of Growth in Epiphyseal PlatePlate

Zone of resting cartilage Zone of resting cartilage • anchors growth plate to boneanchors growth plate to bone

Zone of proliferating cartilageZone of proliferating cartilage• rapid cell division (stacked coins)rapid cell division (stacked coins)

Zone of hypertrophic cartilageZone of hypertrophic cartilage• cells enlarged & remain in cells enlarged & remain in

columnscolumns Zone of calcified cartilageZone of calcified cartilage

• thin zone, cells mostly dead thin zone, cells mostly dead since matrix calcifiedsince matrix calcified

• osteoclasts removing matrixosteoclasts removing matrix• osteoblasts & capillaries move in osteoblasts & capillaries move in

to create bone over calcified to create bone over calcified cartilagecartilage

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Factors Affecting Bone Factors Affecting Bone GrowthGrowth

NutritionNutrition• adequate levels of minerals and vitaminsadequate levels of minerals and vitamins

calcium and phosphorus for bone growthcalcium and phosphorus for bone growth vitamin C for collagen formationvitamin C for collagen formation vitamins K and B12 for protein synthesisvitamins K and B12 for protein synthesis

Sufficient levels of specific hormonesSufficient levels of specific hormones• during childhood need insulinlike growth factorduring childhood need insulinlike growth factor

promotes cell division at epiphyseal platepromotes cell division at epiphyseal plate need hGH (growth), thyroid (T3 &T4) and insulinneed hGH (growth), thyroid (T3 &T4) and insulin

• sex steroids at pubertysex steroids at puberty growth spurt and closure of the epiphyseal growth plategrowth spurt and closure of the epiphyseal growth plate estrogens promote female changes -- wider pelvisestrogens promote female changes -- wider pelvis

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Hormonal AbnormalitiesHormonal Abnormalities

Oversecretion of hGH during childhood Oversecretion of hGH during childhood produces giantismproduces giantism

Undersecretion of hGH or thyroid Undersecretion of hGH or thyroid hormone during childhood produces hormone during childhood produces short statureshort stature

Both men or women that lack estrogen Both men or women that lack estrogen receptors on cells grow taller than receptors on cells grow taller than normalnormal• estrogen responsible for closure of growth estrogen responsible for closure of growth

plateplate

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Bone RemodelingBone Remodeling Ongoing since osteoclasts carve out Ongoing since osteoclasts carve out

small tunnels and osteoblasts rebuild small tunnels and osteoblasts rebuild osteons.osteons.• release calcium and phosphorus into release calcium and phosphorus into

interstitial fluidinterstitial fluid Continual redistribution of bone matrix Continual redistribution of bone matrix

along lines of mechanical stress along lines of mechanical stress • distal femur is fully remodeled every 4 distal femur is fully remodeled every 4

monthsmonths

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Fracture & Repair of BoneFracture & Repair of Bone Fracture is break in a boneFracture is break in a bone Healing is faster in bone than Healing is faster in bone than

in cartilage due to lack of in cartilage due to lack of blood vessels in cartilageblood vessels in cartilage

Healing of bone is still slow Healing of bone is still slow process due to vessel process due to vessel damagedamage

Clinical treatmentClinical treatment• closed reduction = restore closed reduction = restore

pieces to normal position by pieces to normal position by manipulationmanipulation

• open reduction = surgeryopen reduction = surgery

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FracturesFractures Named for shape or position of Named for shape or position of

fracture linefracture line Common types of fractureCommon types of fracture

• closed -- no break in skinclosed -- no break in skin• open fracture --skin brokenopen fracture --skin broken• comminuted -- broken ends of comminuted -- broken ends of

bones are fragmentedbones are fragmented• greenstick -- partial fracturegreenstick -- partial fracture• impacted -- one side of fracture impacted -- one side of fracture

driven into the interior of other sidedriven into the interior of other side• Pott’s -- distal fibular fracturePott’s -- distal fibular fracture• Colles’s -- distal radial fractureColles’s -- distal radial fracture• stress fracture -- microscopic fissuresstress fracture -- microscopic fissures

from repeated strenuous activities from repeated strenuous activities

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Repair of a Fracture (1)Repair of a Fracture (1)

Formation of fracture hematomaFormation of fracture hematoma• damaged blood vessels produce clot in 6-8 hours, bone cells diedamaged blood vessels produce clot in 6-8 hours, bone cells die• inflammation brings in phagocytic cells for clean-up dutyinflammation brings in phagocytic cells for clean-up duty• new capillaries grow into damaged areanew capillaries grow into damaged area

Formation of fibrocartilagenous callus formationFormation of fibrocartilagenous callus formation• fibroblasts invade the procallus & lay down collagen fibersfibroblasts invade the procallus & lay down collagen fibers• chondroblasts produce fibrocartilage to span the broken ends of the bonechondroblasts produce fibrocartilage to span the broken ends of the bone

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Repair of a Fracture (2)Repair of a Fracture (2)

Formation of bony callusFormation of bony callus• osteoblasts secrete spongy bone that joins 2 osteoblasts secrete spongy bone that joins 2

broken ends of bonebroken ends of bone• lasts 3-4 monthslasts 3-4 months

Bone remodelingBone remodeling• compact bone replaces the spongy in the compact bone replaces the spongy in the

bony callusbony callus• surface is remodeled back to normal shapesurface is remodeled back to normal shape

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Calcium Homeostasis & Bone Calcium Homeostasis & Bone TissueTissue

Skeleton is reservoir of Calcium & PhosphateSkeleton is reservoir of Calcium & Phosphate Calcium ions involved with many body systemsCalcium ions involved with many body systems

• nerve & muscle cell functionnerve & muscle cell function• blood clottingblood clotting• enzyme function in many biochemical reactionsenzyme function in many biochemical reactions

Small changes in blood levels of Ca+2 can be Small changes in blood levels of Ca+2 can be deadly (plasma level maintained deadly (plasma level maintained 9-11mg/100mL)9-11mg/100mL)• cardiac arrest if too highcardiac arrest if too high• respiratory arrest if too lowrespiratory arrest if too low

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Exercise & Bone TissueExercise & Bone Tissue Pull on bone by skeletal muscle and Pull on bone by skeletal muscle and

gravity is mechanical stress .gravity is mechanical stress . Stress increases deposition of mineral Stress increases deposition of mineral

salts & production of collagen salts & production of collagen (calcitonin prevents bone loss) (calcitonin prevents bone loss)

Lack of mechanical stress results in Lack of mechanical stress results in bone loss bone loss • reduced activity while in a castreduced activity while in a cast• astronauts in weightlessnessastronauts in weightlessness• bedridden personbedridden person

Weight-bearing exercises build bone Weight-bearing exercises build bone mass mass (walking or weight-lifting)(walking or weight-lifting)

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Aging & Bone TissueAging & Bone Tissue Bone is being built through adolescence, Bone is being built through adolescence,

holds its own in young adults, but is holds its own in young adults, but is gradually lost in aged.gradually lost in aged.

Demineralization = loss of minerals Demineralization = loss of minerals • very rapid in women 40-45 as estrogens levels very rapid in women 40-45 as estrogens levels

decrease decrease • in males, begins after age 60in males, begins after age 60

Decrease in protein synthesisDecrease in protein synthesis• decrease in growth hormonedecrease in growth hormone• decrease in collagen production which gives decrease in collagen production which gives

bone its tensile strengthbone its tensile strength• bone becomes brittle & susceptible to fracturebone becomes brittle & susceptible to fracture

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OsteoporosisOsteoporosis Decreased bone mass resulting in porous Decreased bone mass resulting in porous

bones bones Those at riskThose at risk

• white, thin menopausal, smoking, drinking female white, thin menopausal, smoking, drinking female with family history with family history

• athletes who are not menstruating due to athletes who are not menstruating due to decreased body fat & decreased estrogen levelsdecreased body fat & decreased estrogen levels

• people allergic to milk or with eating disorders people allergic to milk or with eating disorders whose intake of calcium is too lowwhose intake of calcium is too low

Prevention or decrease in severityPrevention or decrease in severity• adequate diet, weight-bearing exercise, & estrogen adequate diet, weight-bearing exercise, & estrogen

replacement therapy (for menopausal women)replacement therapy (for menopausal women)• behavior when young may be most important factor behavior when young may be most important factor

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Disorders of Bone OssificationDisorders of Bone Ossification

RicketsRickets calcium salts are not deposited properlycalcium salts are not deposited properly bones of growing children are softbones of growing children are soft bowed legs, skull, rib cage, and pelvic bowed legs, skull, rib cage, and pelvic

deformities resultdeformities result

OsteomalaciaOsteomalacia new adult bone produced during remodeling new adult bone produced during remodeling

fails to ossifyfails to ossify hip fractures are commonhip fractures are common