6Bones and Joints - Mrs. Pillar's A & P Website

Skeletal System: Bones and Joints6

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Module 5 SkeletalSystem

lEarnToPrEDictDr.thomasMooreandDr.robertarutledgehadworkedtogether for almost two decades, and roberta knewsomething was bothering thomas. She noticed himwincing in pain whenever he bent down to retrievesomething from a bottom shelf, and he was short-temperedratherthanhisusualhappyself.robertaknewthomaswouldneveradmittobeinginjuredif itmeanthe couldn’t care for his patients, even if only for a fewdays.Finally,robertaconvincedhimtoletherx-rayhislowerback.rightaway,whenrobertashowedthomasthex-ray,hepointedtothecauseofthepainhe’dbeensuffering.

using knowledge of the vertebral column, predictthesourceofthomas’spain,basedonhisx-rayshowninthis photo. also, using your knowledge of vertebralanatomy, predict the region of the injury and explainwhythisregionofthevertebralcolumnismorepronetothistypeofinjurythanotherregions.

limitedmovement;othersallownoapparentmovement.Thestruc-tureofagivenjointisdirectlycorrelatedtoitsdegreeofmovement. Althoughtheskeletonisusuallythoughtofastheframeworkofthebody,theskeletalsystemhasmanyotherfunctionsinaddi-tiontosupport.Themajorfunctionsoftheskeletalsysteminclude:

1. Support.Rigid,strongboneiswellsuitedforbearingweightandisthemajorsupportingtissueofthebody.Cartilageprovidesfirmyetflexiblesupportwithincertainstructures,suchasthenose,externalear,thoraciccage,andtrachea.Ligamentsarestrongbandsoffibrousconnectivetissuethatattachtobonesandholdthemtogether.

2. Protection.Boneishardandprotectstheorgansitsurrounds.Forexample,theskullenclosesandprotectsthebrain,andthevertebraesurroundthespinalcord.Theribcageprotectstheheart,lungs,andotherorgansofthethorax.

6.1 FunctionSoFtHESKElEtalSYStEM

Learning Outcome After reading this section, you should be able to

A. Explainthefunctionsoftheskeletalsystem.

Sitting,standing,walking,pickingupapencil,andtakingabreathall involvetheskeletalsystem.Withouttheskeletalsystem,therewould be no rigid framework to support the soft tissues of thebody and no system of joints and levers to allow the body tomove.Theskeletalsystemconsistsofbones,suchasthoseshowninfigure6.1,aswellastheirassociatedconnectivetissues,whichinclude cartilage, tendons, and ligaments. The term skeleton isderivedfromaGreekwordmeaningdried.Buttheskeletonisfarfrombeingdryandnonliving.Rather,theskeletalsystemconsistsofdynamic,livingtissuesthatareabletogrow,detectpainstimuli,adapttostress,andundergorepairafterinjury. A joint,oranarticulation, isaplacewheretwobonescometogether.Manyjointsaremovable,althoughsomeofthemallowonly

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SkeletalSystem:BonesandJoints 111Skeletal

3. Movement.Skeletalmusclesattachtobonesbytendons,whicharestrongbandsofconnectivetissue.Contractionoftheskeletalmusclesmovesthebones,producingbodymovements.Joints,wheretwoormorebonescometogether,allowmovementbetweenbones.Smoothcartilagecoverstheendsofboneswithinsomejoints,allowingthebonestomovefreely.Ligamentsallowsomemovementbetweenbonesbutpreventexcessivemovement.

4. Storage.Somemineralsintheblood—principally,calciumandphosphorus—aretakenintoboneandstored.Shouldbloodlevelsofthesemineralsdecrease,themineralsarereleasedfromboneintotheblood.Adiposetissueisalsostoredwithinbonecavities.Ifneeded,thelipidsarereleasedintothebloodandusedbyothertissuesasasourceofenergy.

5. Blood cell production.Manybonescontaincavitiesfilledwithredbonemarrow,whichproducesbloodcellsandplatelets(seechapter11).

6.2 ExtracEllularMatrixLearning Outcome After reading this section, you should be able to

A. Describethecomponentsoftheextracellularmatrix,andexplainthefunctionofeach.

Thebone,cartilage,tendons,andligamentsoftheskeletalsystemare all connective tissues. Their characteristics are largely deter-minedbythecompositionoftheirextracellularmatrix.Thematrixalways contains collagen, ground substance, and other organic

molecules,aswellaswaterandminerals.Butthetypesandquan-titiesofthesesubstancesdifferineachtypeofconnectivetissue. Collagen (kol′lă-jen; koila, glue + -gen, producing) is atough,ropelikeprotein.Proteoglycans(prō′tē-ō-glī′kanz;proteo,protein+glycan,polysaccharide)arelargemoleculesconsistingofpolysaccharidesattachedtocoreproteins,muchastheneedlesofapinetreeareattachedtothetree’sbranches.Theproteoglycansformlargeaggregates,muchaspinebranchescombinetoformawholetree.Proteoglycanscanattractandretainlargeamountsofwaterbetweentheirpolysaccharide“needles.” Theextracellularmatrixof tendons and ligaments containslarge amounts of collagen fibers, making these structures verytough, like ropes or cables. The extracellular matrix of cartilage(kar′ti-lij) contains collagen and proteoglycans. Collagen makescartilage tough, whereas the water-filled proteoglycans make itsmoothandresilient.Asaresult,cartilageisrelativelyrigid,butit springs back to its original shape after being bent or slightlycompressed.Itisanexcellentshockabsorber. Theextracellularmatrixofbonecontainscollagenandminer-als,includingcalciumandphosphate.Theropelikecollagenfibers,likethereinforcingsteelbarsinconcrete,lendflexiblestrengthtothe bone. The mineral component, like the concrete itself, givesthe bone compression (weight-bearing) strength. Most of themineralinboneisintheformofcalciumphosphatecrystalscalledhydroxyapatite(hī-drok′sē-ap-ă-tīt).

Predict 2

What would a bone be like if all of the minerals were removed? What would it be like if all of the collagen were removed?

acaSEinPoint

Brittle Bone Disease

Maytrix isa10-year-old girlwhohasahistory ofnumerous brokenbones.atfirst,physicianssuspectedshewasavictimofchildabuse,but eventually they determined that she has brittle bone disease,or osteogenesis imperfecta, which literally means imperfect boneformation. May is short for her age, and her limbs are short andbowed.Hervertebralcolumnisalsoabnormallycurved.Brittlebonedisease is a rare disorder caused by any one of a number of faultygenes that results in either too little collagen formation or poorqualitycollagen.asaresult,thebonematrixhasdecreasedflexibilityandismoreeasilybrokenthannormalbone.

6.3 GEnEralFEaturESoFBonELearning Outcomes After reading this section, you should be able to

A. Explainthestructuraldifferencesbetweencompactboneandspongybone.

B. outlinetheprocessesofboneossification,growth,remodeling,andrepair.

Therearefourcategoriesofbone,basedontheirshape:long,short,flat,andirregular.Long bonesarelongerthantheyarewide.Mostofthebonesoftheupperandlower limbsare longbones.Short bones areapproximatelyasbroadas theyare long;examplesarethebonesofthewristandankle.Flat boneshavearelativelythin,

Skull

Sternum

RadiusUlna

Vertebralcolumn

Ribs

Clavicle

Humerus

Femur

Tibia

Fibula

Pelvis

Figure 6.1 Major Bones of the Skeletal System


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StructureofalongBoneAlongboneservesasausefulmodelforillustratingthepartsofa typical bone (figure 6.2). Each long bone consists of a centralshaft,calledthediaphysis(dī-af′i-sis;growingbetween),andtwo

flattenedshape.Examplesofflatbonesarecertainskullbones,theribs, the scapulae (shoulder blades), and the sternum. Irregular bones include thevertebraeandfacialbones,whichhaveshapesthatdonotfitreadilyintotheotherthreecategories.

Epiphysis

Articular cartilage

Diaphysis

Compact bone

Medullary cavity (containsred marrow in juveniles andyellow marrow in adults)

Periosteum

Endosteum

Epiphyseal linesin adults

Epiphyseal platesin juveniles

Diaphysis

Spongy bone

Adult bone

Young bone

Endosteum

Central canals

Connecting vessels

Osteons(haversian systems)

Inner layer

Outerlayer

Compact bone

Medullarycavity

Periosteum

Spongy bonewith trabeculae

Adult bone

Figure 6.2 Structure of a Long Bone(a)Younglongbone(thefemur)showingtheepiphysis,epiphysealplates,anddiaphysis.(b)adultlongbonewithepiphyseallines.(c)internalfeaturesofaportionofthediaphysisin(a).

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(c)

(b)



HistologyofBoneThe periosteum and endosteum contain osteoblasts (os′tē-ō-blasts; bone-forming cells), which function in the formation ofbone, as well as in the repair and remodeling of bone. Whenosteoblastsbecomesurroundedbymatrix,theyarereferredtoasosteocytes(os′tē-ō-sītz;bonecells). Bone is formed in thin sheets of extracellular matrix calledlamellae (lă-mel′ē; plates), with osteocytes located between thelamellae within spaces called lacunae (lă-koo′nē; a hollows)(figure6.3).Cellprocessesextendfromtheosteocytesacrosstheextracellularmatrixofthelamellaewithintinycanalscalledcana-liculi(kan-ă-lik′ū-lī;sing.canaliculus,littlecanal). Therearetwomajortypesofbone,basedontheirhistologicalstructure.Compact boneismostlysolidmatrixandcells.Spongy bone,orcancellous(kan′sĕ-lŭs)bone,consistsofalacynetworkofbonewithmanysmall,marrow-filledspaces.

Compact BoneCompactbone(figure6.3)formsmostofthediaphysisoflongbonesandthe thinnersurfacesofallotherbones.Mostof the lamellaeofcompactboneareorganizedintosetsofconcentricrings,witheachsetsurroundingacentral canal,orHaversian(ha-ver′shan)canal.Bloodvesselsthatrunparalleltothelongaxisoftheboneare contained within the central canals. Each central canal, withthe lamellae and osteocytes surrounding it, is called an osteon(os′tē-on),orHaversian system.Eachosteon,seenincrosssection,lookslikeamicroscopictarget,withthecentralcanalasthe“bull’s-eye”(figure6.3).Osteocytes,locatedinlacunae,areconnectedtooneanotherbycellprocessesincanaliculi.Thecanaliculigivetheosteontheappearanceofhavingtinycrackswithinthelamellae.

ends,eachcalledanepiphysis(e-pif′i-sis;growingupon).Athinlayerofarticular(ar-tik′ū-lăr;joint)cartilagecoverstheendsoftheepiphyseswherethebonearticulates(joins)withotherbones.A long bone that is still growing has an epiphyseal plate, orgrowth plate, composedof cartilage,betweeneachepiphysis andthediaphysis(figure6.2a).Theepiphysealplateiswherethebonegrows in length. When bone growth stops, the cartilage of eachepiphysealplate is replacedbyboneandbecomesanepiphyseal line(figure6.2b). Bonescontaincavities,suchasthelargemedullary cavityinthediaphysis, aswellas smallercavities in theepiphysesof longbones and in the interior of other bones. These spaces are filledwith soft tissue called marrow. Yellow marrow consists mostlyof adipose tissue. Red marrow consists of blood-forming cellsandistheonlysiteofbloodformationinadults(seechapter11).Children’s bones have proportionately more red marrow thando adult bones because, as a person ages, red marrow is mostlyreplacedbyyellowmarrow.Inadults, redmarrowisconfinedtothebonesinthecentralaxisofthebodyandinthemostproximalepiphysesofthelimbs. Mostoftheoutersurfaceofboneiscoveredbydenseconnec-tive tissue called the periosteum (per-ē-os′tē-ŭm; peri, around+osteon,bone),whichcontainsbloodvesselsandnerves(figure6.2c).Thesurfaceofthemedullarycavityislinedwithathinnerconnec-tivetissuemembrane,theendosteum(en-dos′tē-ŭm;endo,inside).

Lamellae between osteons

Periosteum

Blood vesselconnecting to a central canalbetween osteons

Blood vesselsconnecting to a central canal

Blood vesselswithin a central(Haversian) canal

Lamellae on surface of boneConcentric rings

of lamellae

OsteonOsteon

Blood vessel withinthe periosteum

Canaliculi

Osteocytes inlacunae

Canaliculi

Lacunae

Central canal

LM 400x

(a)(b)

Figure 6.3 Structure of Bone Tissue(a)Photomicrographofcompactbone.(b)Finestructureofcompactbone.


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BoneossificationOssification (os′i-fi-kā′shŭn; os, bone+ facio, to make) is theformation of bone by osteoblasts. After an osteoblast becomescompletely surrounded by bone matrix, it becomes a maturebone cell, or osteocyte. In the fetus, bones develop by two pro-cesses,eachinvolvingtheformationofbonematrixonpreexistingconnectivetissue(figure6.5).Boneformationthatoccurswithinconnective tissue membranes is called intramembranous ossifi-cation, and bone formation that occurs inside cartilage is calledendochondralossification.Bothtypesofboneformationresultincompactandspongybone.

Nutrients leave the blood vessels of the central canals anddiffuse to the osteocytes through the canaliculi. Waste productsdiffuseintheoppositedirection.Thebloodvesselsinthecentralcanals, inturn,areconnectedtobloodvessels intheperiosteumandendosteum.

Spongy BoneSpongybone,socalledbecauseofitsappearance,islocatedmainlyin the epiphyses of long bones. It forms the interior of all otherbones. Spongy bone consists of delicate interconnecting rods orplates of bone called trabeculae (tră-bek′ū-lē; beams), whichresemblethebeamsorscaffoldingofabuilding(figure6.4a).Likescaffolding, the trabeculae add strength to a bone without theadded weight that would be present if the bone were solid min-eralizedmatrix.Thespacesbetween the trabeculaeare filledwithmarrow.Eachtrabeculaconsistsofseverallamellaewithosteocytesbetweenthem(figure6.4b).Usually,nobloodvesselspenetratethetrabeculae, and the trabeculae have no central canals. Nutrientsexitvesselsinthemarrowandpassbydiffusionthroughcanaliculitotheosteocytesofthetrabeculae.

Trabeculae

Spaces containingbone marrow andblood vessels

Compact bone

Spongybone

Osteoblast

Osteoclast

Osteocyte

Lamellae Canaliculus

Trabecula

Parietalbone

Ossificationcenter

OssificationcenterSuperior part

of occipitalbone

Inferior partof occipital bone

Temporal bone

Vertebrae

Styloidprocess

Mandible

Maxilla

Zygomatic bone

Frontal bone

Nasal bone

Ethmoid bone

Sphenoid bone

Intramembranousbones forming

Fontanel

Cartilage

Endochondralbones forming

Figure 6.4 Spongy Bone(a)Beamsofbone,thetrabeculae,surroundspacesinthebone.inlife,thespacesarefilledwithredoryellowbonemarrowandwithbloodvessels.(b)transversesectionofatrabecula.

Figure 6.5 Bone Formation in a Fetus(a)intramembranousossificationoccursina12-week-oldfetusatossificationcentersintheflatbonesoftheskull(yellow).Endochondralossificationoccursinthebonesformingtheinferiorpartoftheskull(blue).(b)radiographofan18-week-oldfetus,showingintramembranousandendochondralossification.intramembranousossificationoccursatossificationcentersintheflatbonesoftheskull.Endochondralossificationhasformedbonesinthediaphysesoflongbones.theepiphysesarestillcartilageatthisstageofdevelopment.

(a)

(b)

(a)

(b)



increase in number, enlarge, and die. Then the cartilage matrixbecomescalcified(figure6.6,step2).Asthisprocessisoccurringin thecenterof thecartilagemodel,bloodvesselsaccumulate inthe perichondrium. The presence of blood vessels in the outersurfaceoffuturebonecausessomeoftheunspecifiedconnectivetissuecellsonthesurfacetobecomeosteoblasts.Theseosteoblaststhen produce a collar of bone around part of the outer surfaceof thediaphysis, and theperichondriumbecomesperiosteum inthatarea.Bloodvesselsalsogrowintothecenterofthediaphyses,bringing in osteoblasts and stimulating ossification. The centerpartof thediaphysis,wherebonefirstbeginstoappear, iscalledthe primary ossification center (figure 6.6, step 3). Osteoblastsinvadespacesinthecenteroftheboneleftbythedyingcartilagecells. Some of the calcified cartilage matrix is removed by cellscalled osteoclasts (os′tē-ō-klastz; bone-eating cells), and theosteoblastslineupontheremainingcalcifiedmatrixandbeginto

Intramembranous(in′tră-mem′brā-nŭs)ossificationoccurswhen osteoblasts begin to produce bone in connective tissuemembranes. This occurs primarily in the bones of the skull.Osteoblastslineuponthesurfaceofconnectivetissuefibersandbegin depositing bone matrix to form trabeculae. The processbegins in areas called ossification centers (figure 6.5a), and thetrabeculaeradiateoutfromthecenters.Usually,twoormoreossi-ficationcentersexist ineach flat skullbone,and the skullbonesresultfromfusionofthesecentersastheyenlarge.Thetrabeculaeare constantly remodeled after their initial formation, and theymayenlargeorbereplacedbycompactbone. Thebonesat thebaseoftheskullandmostoftheremainingskeletal system develop through the process of endochondral ossification from cartilage models. The cartilage models havethegeneralshapeofthematurebone(figure6.6,step1).Duringendochondral ossification, cartilage cells, called chondrocytes,

Perichondrium

Cartilage

Perichondrium

Bone collar

Uncalcifiedcartilage

Calcified cartilage

Periosteum

Blood vesselto periosteum

Epiphysis

Epiphysis

Diaphysis

A cartilage model, with the general shape of the mature bone, is produced by chondrocytes. A perichondrium surrounds most of the cartilage model.

2. The chondrocytes enlarge, and cartilage is calcified. A bone collar is produced, and the perichondrium of the diaphysis becomes the periosteum.

3. A primary ossification center forms as blood vessels and osteoblasts invade the calcified cartilage. The osteoblasts lay down bone matrix, forming trabeculae.

4. Secondary ossification centers form in the epiphyses of long bones.

Perichondrium

Bone collar

Cartilage

Calcified cartilage

Periosteum

Blood vessel

Primaryossificationcenter

Trabecula

Medullary cavity

Secondaryossificationcenter

Spongybone

Cartilage

Blood vessel

Calcifiedcartilage

Spongy bone

PeriosteumBone collar

Blood vessel

Medullary cavity

Space inbone

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43

Perichondrium

Cartilage

Perichondrium

Bone collar

Uncalcifiedcartilage

Calcified cartilage

Periosteum

Blood vesselto periosteum

Epiphysis

Epiphysis

Diaphysis

A cartilage model, with the general shape of the mature bone, is produced by chondrocytes. A perichondrium surrounds most of the cartilage model.

2. The chondrocytes enlarge, and cartilage is calcified. A bone collar is produced, and the perichondrium of the diaphysis becomes the periosteum.

3. A primary ossification center forms as blood vessels and osteoblasts invade the calcified cartilage. The osteoblasts lay down bone matrix, forming trabeculae.

4. Secondary ossification centers form in the epiphyses of long bones.

Perichondrium

Bone collar

Cartilage

Calcified cartilage

Periosteum

Blood vessel

Primaryossificationcenter

Trabecula

Medullary cavity

Secondaryossificationcenter

Spongybone

Cartilage

Blood vessel

Calcifiedcartilage

Spongy bone

PeriosteumBone collar

Blood vessel

Medullary cavity

Space inbone

1 2

43

PROCESS Figure 6.6 Endochondral Ossification of a Long Bone


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ofthebone,causingthebonetoelongate.Thenthechondrocytesenlargeanddie.Thecartilagematrixbecomescalcified.Muchofthe cartilage that forms around the enlarged cells is removed byosteoclasts, and the dying chondrocytes are replaced by osteo-blasts. The osteoblasts start forming bone by depositing bonelamellae on the surface of the calcified cartilage. This processproducesboneonthediaphysealsideoftheepiphysealplate.

Predict 3

Describe the appearance of an adult if cartilage growth did not occur in the long bones during childhood.

BoneremodelingBone remodelinginvolvestheremovalofexistingbonebyosteoclastsandthedepositionofnewbonebyosteoblasts.Boneremodelingoccursinallbone.Remodelingisresponsibleforchangesinboneshape,theadjustmentofbonetostress,bonerepair,andcalciumionregulationinthebodyfluids.Remodelingisalsoinvolvedin

formbonetrabeculae.Asthebonedevelops,itisconstantlychanging.Amedullarycavityformsinthecenterofthediaphysisasosteo-clastsremoveboneandcalcifiedcartilage,whicharereplacedbybone marrow. Later, secondary ossification centers form in theepiphyses(figure6.6,step4).

BoneGrowthBonegrowthoccursbythedepositionofnewbonelamellaeontoexisting bone or other connective tissue. As osteoblasts depositnewbonematrixonthesurfaceofbonesbetweentheperiosteumand the existing bone matrix, the bone increases in width, ordiameter. This process is called appositional growth. Growth inthelengthofabone,whichisthemajorsourceofincreasedheightinanindividual,occursintheepiphysealplate.Thistypeofbonegrowth occurs through endochondral ossification (figure 6.7).Chondrocytes increase in number on the epiphyseal side of theepiphysealplate.Theylineupincolumnsparalleltothelongaxis

Calcified cartilageis replaced by bone.

Chondrocytesdivide and enlarge.

Length of boneincreases.

Thickness ofepiphysealplate remainsunchanged.

Bone isadded todiaphysis.

Bone of diaphysis

Epiphysealplate

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Femur

Patella

Epiphysis

Epiphysealplate

Diaphysis

New cartilage isproduced on the epiphyseal sideof the plate as thechondrocytes divideand form stacksof cells.

Chondrocytesmature and enlarge.

Matrix is calcified,and chondrocytesdie.

The cartilage onthe diaphyseal sideof the plate isreplaced by bone.

Epiphyseal side

Diaphyseal side

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4LM 400x

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4

PROCESS Figure 6.7 Endochondral Bone Growth(a)locationoftheepiphysealplateinalongbone.(b)asthechondrocytesoftheepiphysealplatedivideandalignincolumns,thecartilageexpandstowardtheepiphysis,andtheboneelongates.atthesametime,theoldercartilageiscalcifiedandthenreplacedbybone,whichisremodeled,resultinginexpansionofthemedullarycavityofthediaphysis.thenetresultisanepiphysealplatethatremainsuniforminthicknessthroughtimebutisconstantlymovingtowardtheepiphysis,resultinginelongationofthebone.(c)Photomicrographofanepiphysealplate,demonstratingchondrocytedivisionandenlargementandtheareasofcalcificationandossification.

(c)

(b)

(a)



Compactbone

Periosteum

Medullarycavity

ClotDeadbone

Newbone

Compactbone atbreak site

Spongybone

Deadbone

Cartilage

Fibersand cartilage

Clot formation Callus formation Callus ossification Bone remodeling

1 When a bone is broken, a clot forms in the damaged area.

2 Blood vessels and cells invade the clot and produce a network of fibers and cartilage called a callus.

3 Osteoblasts enter the callus and form spongy bone.

4 Most of the spongy bone is slowly remodeled to form compact bone and the repair is complete.

Callus

PROCESS Figure 6.8 Bone Repair

bonegrowthwhennewly formedspongybone in theepiphysealplate forms compact bone. A long bone increases in length anddiameterasnewboneisdepositedontheoutersurfaceandgrowthoccursattheepiphysealplate.Atthesametime,boneisremovedfromtheinner,medullarysurfaceofthebone.Asthebonediameterincreases,thethicknessofthecompactbonerelativetothemedul-larycavitytendstoremainfairlyconstant.Ifthesizeofthemedullarycavity did not also increase as bone size increased, the compactboneofthediaphysiswouldbecomethickandveryheavy. Becauseboneisthemajorstoragesiteforcalciuminthebody,bone remodeling is important to maintain blood calcium levelswithinnormallimits.Calciumisremovedfromboneswhenbloodcalciumlevelsdecrease,anditisdepositedwhendietarycalciumisadequate.Thisremovalanddepositionisunderhormonalcontrol(see“BoneandCalciumHomeostasis”laterinthischapter). If too much bone is deposited, the bones become thick ordevelopabnormalspursor lumpsthatcan interferewithnormalfunction.Toolittleboneformationortoomuchboneremoval,asoccurs inosteoporosis,weakens thebonesandmakes themsus-ceptibletofracture(seeSystemsPathology,“Osteoporosis”).

BonerepairSometimesaboneisbrokenandneedstoberepaired.Whenthisoccurs, blood vessels in the bone are also damaged. The vesselsbleed, and a clot forms in the damaged area (figure 6.8, step 1).Two to three days after the injury, blood vessels and cells fromsurrounding tissuesbegin to invade theclot.Someof thesecellsproduceafibrousnetworkofconnectivetissuebetweenthebrokenbones,whichholdsthebonefragmentstogetherandfillsthegapbetweenthem.Othercellsproduceisletsofcartilageinthefibrousnetwork.Thenetworkoffibersandisletsofcartilagebetweenthetwobonefragmentsiscalledacallus(figure6.8,step2).

Osteoblastsenter thecallusandbegin formingspongybone(figure6.8,step3).Spongyboneformationinthecallusisusuallycomplete4–6weeksaftertheinjury.Immobilizationoftheboneiscriticaluptothistimebecausemovementcanrefracturethedeli-catenewmatrix.Subsequently,thespongyboneisslowlyremod-eledtoformcompactandspongybone,andtherepairiscomplete(figure6.8,step4).Althoughimmobilizationatafracturepointiscriticalduringtheearlystagesofbonehealing,completeimmobili-zationisnotgoodforthebone,themuscles,orthejoints.Notlongago,itwascommonpracticetoimmobilizeabonecompletelyforaslongas10weeks.Butwenowknowthat,ifaboneisimmobi-lizedforaslittleas2weeks,themusclesassociatedwiththatbonemayloseasmuchashalftheirstrength.Furthermore,ifaboneiscompletelyimmobilized,itisnotsubjectedtothenormalmechanicalstressesthathelpitform.Bonematrixisreabsorbed,andthestrengthofthebonedecreases.Inexperimentalanimals,completeimmobili-zationofthebackfor1monthresultedinuptoathreefolddecreasein vertebral compression strength. Modern therapy attempts tobalancebone immobilizationwithenoughexercise tokeepmuscleandbonefromdecreasinginsizeandstrengthandtomaintainjointmobility.Thesegoals areaccomplishedby limiting theamountoftimeacastisleftonthepatientandbyusing“walkingcasts,”whichallowsomestressontheboneandsomemovement.Totalhealingofthefracturemayrequireseveralmonths.Ifabonehealsproperly,thehealedregioncanbeevenstrongerthantheadjacentbone.

6.4 BonEanDcalciuMHoMEoStaSiSLearning Outcomes After reading this section, you should be able to

A. Explaintheroleofboneincalciumhomeostasis.B. Describehowparathyroidhormoneandcalcitonininfluence

bonehealthandcalciumhomeostasis.


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al Bone fractures can be classi-fied as open (or compound), if the boneprotrudes through the skin, and closed(or simple), if the skin is not perforated.Figure 6a illustrates some of the differenttypes of fractures. if the fracture totallyseparates the two bone fragments, it iscalled complete; if it doesn’t, it is calledincomplete. an incomplete fracture thatoccursontheconvexsideofthecurveofaboneiscalledagreenstick fracture.acom-minuted (kom′i-nū-ted; broken into smallpieces) fracture is one in which the bonebreaks into more than two fragments. animpacted fracture occurs when one of thefragmentsofonepartoftheboneisdrivenintothespongyboneofanotherfragment.

Fracturescanalsobeclassifiedaccord-ing to the direction of the fracture line aslinear(paralleltothelongaxis);transverse

(atrightanglestothelongaxis);orobliqueor spiral (at an angle other than a rightangletothelongaxis).

CLINICALIMPACT Bone Fractures

Complete

Linear

Incomplete

Comminuted

Transverse

Impacted

Oblique

Spiral

Figure 6A typesofbonefractures.

PTH

Osteoclastspromote Ca2+

uptake frombone.

Osteoblasts promoteCa2+ deposition in bone.

Stimulatesosteoclasts

Inhibitsosteoclasts

Bone

Ca2+

Ca2+ Blood

Vitamin D

Kidney

Small intestine

Calcitonin

Decreased blood Ca2+ stimulates PTH secretion from parathyroid glands.

PTH stimulates osteoclasts to break down

bone and release Ca2+ into the blood.

In the kidneys, PTH increases Ca2+ reabsorption from the urine. PTH also stimulates active Vitamin D formation.

Vitamin D promotes Ca2+ absorption from the small intestine into the blood.

Increased blood Ca2+ stimulates calcitonin secretion from the thyroid gland.

Calcitonin inhibits osteoclasts, which allows for enhanced osteoblast uptake of Ca2+ from the blood to deposit into bone.

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6

Posterior aspectof thyroid gland

Parathyroidglands

Thyroid gland

Increasedblood Ca2+

Decreasedblood Ca2+

PROCESS Figure 6.9 Calcium Homeostasis



Calcitonin (kal-si-tō′nin), secreted from the thyroid glandwhenbloodcalciumlevelsaretoohigh,decreasesosteoclastactivityand thus decreases blood calcium levels. Increasing blood cal-ciumlevelsstimulatecalcitoninsecretion.PTHandcalcitoninaredescribedmorefullyinchapter10.

6.5 GEnEralconSiDErationSoFBonEanatoMY


A. listanddefinethemajorfeaturesofatypicalbone.

It is traditional to list 206 bones in the average adult skeleton(table 6.1), although the actual number varies from person topersonanddecreaseswithageassomebonesfuse. Anatomists use several common terms to describe the fea-turesofbones(table6.2).Forexample,aholeinaboneiscalledaforamen(fō-rā′men;pl.foramina,fō-rā′min-ă;foro,topierce).Aforamenusuallyexistsinabonebecausesomestructure,suchasanerveorbloodvessel,passesthroughtheboneatthatpoint.Iftheholeiselongatedintoatunnel-likepassagethroughthebone,

Boneisthemajorstoragesiteforcalciuminthebody,andmove-ment of calcium into and out of bone helps determine bloodcalcium levels, which is critical for normal muscle and nervoussystem function. Calcium (Ca2+) moves into bone as osteoblastsbuildnewboneandoutofboneasosteoclastsbreakdownbone(figure 6.9). When osteoblast and osteoclast activity is balanced,themovementsofcalciumintoandoutofaboneareequal. When blood calcium levels are too low, osteoclast activityincreases, osteoclasts release calcium from bone into the blood,and blood calcium levels increase. Conversely, if blood cal-ciumlevelsaretoohigh,osteoclastactivitydecreases,osteoblastsremovecalciumfromthebloodtoproducenewbone,andbloodcalciumlevelsdecrease. Calcium homeostasis is maintained by two hormones.Parathyroid hormone (PTH), secreted from the parathyroidglandswhenbloodcalciumlevelsaretoolow,stimulatesincreasedbonebreakdownandincreasedbloodcalciumlevelsbyindirectlystimulatingosteoclastactivity.PTHalsoincreasescalciumuptakefromtheurineinthekidney.Additionally,PTHstimulatesthekid-neystoformactivevitaminD,whichincreasescalciumabsorptionfromthesmallintestine.DecreasingbloodcalciumlevelsstimulatePTHsecretion.

TABle 6.1 Named Bones in the Adult Human Skeleton

Bones NumberThoracic Cage ribs 24 Sternum(3parts,sometimesconsidered3bones) 1

total thoracic cage 25

total axial skeleton 80

Appendicular Skeleton

Pectoral Girdle Scapula 2 clavicle 2

Upper Limb Humerus 2 ulna 2 radius 2 carpalbones 16 Metacarpalbones 10 Phalanges 28

total girdle and upper limb 64

Pelvic Girdle coxalbone 2

Lower Limb Femur 2 tibia 2 Fibula 2 Patella 2 tarsalbones 14 Metatarsalbones 10 Phalanges 28

total girdle and lower limb 62

total appendicular skeleton 126

total bones 206

Bones NumberAxial Skeleton

Skull Braincase Paired Parietal 2 temporal 2 unpaired Frontal 1 occipital 1 Sphenoid 1 Ethmoid 1

Face Paired Maxilla 2 Zygomatic 2 Palatine 2 nasal 2 lacrimal 2 inferiornasalconcha 2

unpaired Mandible 1 Vomer 1

total skull 22

Auditory Ossicles Malleus 2 incus 2 Stapes 2

total 6

Hyoid 1

Vertebral Column cervicalvertebrae 7 thoracicvertebrae 12 lumbarvertebrae 5 Sacrum 1 coccyx 1

total vertebral column 26


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TABle 6.2 Anatomical Terms for Features of Bones

Term DescriptionMajor Features

Body,shaft Mainportion

Head Enlarged(oftenrounded)end

neck constrictedareabetweenheadandbody

condyle Smooth,roundedarticularsurface

Facet Small,flattenedarticularsurface

crest Prominentridge

Process Prominentprojection

tubercle,ortuberosity Knoborenlargement

trochanter largetuberosityfoundonlyon proximalfemur

Epicondyle Enlargementnearoraboveacondyle

Openings or Depressions

Foramen Hole

canal,meatus tunnel

Fissure cleft

Sinus cavity

Fossa Depression

itiscalledacanalorameatus(mē-ā′tus;apassage).Adepressionin a bone is called a fossa (fos′ă). A lump on a bone is called atubercle(too′ber-kl;aknob)oratuberosity(too′ber-os′i-tē),andaprojectionfromabone iscalledaprocess.Most tuberclesandprocesses are sites of muscle attachment on the bone. Increasedmuscle pull, as occurs when a person lifts weights to build upmusclemass,canincreasethesizeofsometubercles.Thesmooth,roundedendofabone,whereitformsajointwithanotherbone,iscalledacondyle(kon′dīl;knuckle). Thebonesof the skeletonaredivided intoaxialandappen-dicularportions(figure6.10).

6.6 axialSKElEtonLearning Outcomes After reading this section, you should be able to

A. namethebonesoftheskullanddescribetheirmainfeaturesasseenfromthelateral,frontal,internal,andinferiorviews.

B. listthebonesthatformthemajorityofthenasalseptum.C. Describethelocationsandfunctionsoftheparanasalsinuses.D. listthebonesofthebraincaseandtheface.e. Describetheshapeofthevertebralcolumn,andlistits

divisions.F. Discussthecommonfeaturesofthevertebraeandcontrast

vertebraefromeachregionofthevertebralcolumn.G. listthebonesandcartilageoftheribcage,includingthethree

typesofribs.

Theaxialskeletoniscomposedoftheskull,thevertebralcolumn,andthethoraciccage.

SkullThe22bonesoftheskullaredividedintothoseofthebraincaseandthoseoftheface(seetable6.1).Thebraincase,whichenclosesthecranialcavity,consistsof8bones that immediatelysurroundand protect the brain; 14 facial bones form the structure of theface.Thirteenof the facialbonesare rather solidlyconnected toformthebulkoftheface.Themandible,however,formsafreelymovablejointwiththerestoftheskull.Therearealsothreeaudi-toryossicles(os′i-klz)ineachmiddleear(sixtotal). Manystudentsstudyinganatomyneverseetheindividualbonesoftheskull.Eveniftheydo,itmakesmoresensefromafunctional,or clinical, perspective to study most of the bones as they appeartogetherintheintactskullbecausemanyoftheanatomicalfeaturesof theskullcannotbefullyappreciatedbyexaminingtheseparatebones.Forexample,severalridgesontheskullcrossmorethanonebone,andseveralforaminaare locatedbetweenbonesratherthanwithinasinglebone.Forthesereasons,itismorerelevanttothinkof the skull, excluding themandible, as a singleunit.Themajorfeaturesoftheintactskullarethereforedescribedfromfourviews.

Lateral ViewTheparietal bones(pă-rī′ĕ-tăl;wall)andtemporal(tem′pō-răl)bonesformalargeportionofthesideofthehead(figure6.11).(Theword temporal refers to time,and the temporalbone is sonamedbecausethehairsofthetemplesturnwhite,indicatingthepassageoftime.)Thesetwobonesjoineachotheronthesideoftheheadatthesquamous(skwā′mŭs)suture.Asutureisajointunitingbonesof theskull.Anteriorly, theparietalbone is joinedtothefrontal(forehead)bonebythecoronal(kōr′ō-năl;corona,crown)suture,andposteriorlyitisjoinedtotheoccipital(ok-sip′i-tăl;backofthehead)bonebythelambdoid(lam′doyd)suture.Aprominentfea-tureofthetemporalboneisalargeopening,theexternal auditory canal,acanal thatenablessoundwaves toreachtheeardrum.Themastoid(mas′toyd)processofthetemporalbonecanbeseenandfeltasaprominentlumpjustposteriortotheear.Importantneckmusclesinvolvedinrotationoftheheadattachtothemastoidprocess. Partofthesphenoid(sfē′noyd)bonecanbeseenimmediatelyanteriortothetemporalbone.Althoughitappearstobetwosmall,pairedbonesonthesidesoftheskull,thesphenoidboneisactuallyasinglebonethatextendscompletelyacrosstheskull.Itresemblesabutterfly,with itsbody in thecenterof the skull and itswingsextendingtothesidesoftheskull.Anteriortothesphenoidboneisthezygomatic(zī-gō-mat′ik)bone,orcheekbone,whichcanbeeasilyfelt.Thezygomatic arch,whichconsistsofjoinedprocessesof the temporal and zygomatic bones, forms a bridge across thesideofthefaceandprovidesamajorattachmentsiteforamusclemovingthemandible. The maxilla (mak-sil′ă; jawbone) forms the upper jaw, andthemandible (man′di-bl; jaw) forms the lower jaw.Themaxillaarticulatesbysuturestothetemporalbone.Themaxillacontainsthesuperiorsetofteeth,andthemandiblecontainstheinferiorteeth.

Frontal ViewThemajorstructuresseenfromthefrontalviewarethefrontalbone,thezygomaticbones,themaxillae,andthemandible(figure6.12a).Theteethareveryprominentinthisview.Manybonesofthefacecanbeeasilyfeltthroughtheskin(figure6.12b).



UlnaRadius

Carpal bonesMetacarpalbones

Phalanges

Coxalbone

Femur

Patella

Tibia

Fibula

Tarsal bones

Metatarsal bones

Phalanges

Anterior view Posterior view

Axial Skeleton

Skull

Vertebralcolumn

Mandible

Ribs

Sacrum

Coccyx

Appendicular Skeleton

Clavicle

Scapula

Humerus

Axial Skeleton

Skull

Vertebralcolumn

Mandible

Hyoid bone

Sternum

Ribs

Sacrum

Figure 6.10 Complete SkeletonBonesoftheaxialskeletonarelistedinthefarleft-andright-handcolumns;bonesoftheappendicularskeletonarelistedinthecenter.(theskeletonisnotshownintheanatomicalposition.)


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Coronal suture

Parietal bone

Temporal bone

Occipital bone

Squamous suture

Lambdoid suture

External auditory canal

Styloid process

Zygomatic arch

Frontal bone

Sphenoid bone

Nasal bone

Lacrimal bone

Ethmoid bone

Zygomatic bone

Maxilla

Mental foramen

Nasolacrimal canal

Mastoid process

Mandible

Mandibular condyle

Coronoid process

Lateral view

Figure 6.11 Skull as Seen from the Right Side (The names of bones are in bold.)

Fromthisview, themostprominentopenings into the skullaretheorbits(ōr′bitz;eyesockets)andthenasal cavity.Theorbitsarecone-shapedfossae, sonamedbecause theeyesrotatewithinthem.Thebonesoftheorbitsprovidebothprotectionfortheeyesandattachmentpointsforthemusclesthatmovetheeyes.Theorbitisagoodexampleofwhyitisvaluabletostudytheskullasanintactstructure.Nofewerthansevenbonescometogethertoformtheorbit,andforthemostpart,thecontributionofeachbonetotheorbitcannotbeappreciatedwhenthebonesareexaminedindividually. Each orbit has several openings through which structurescommunicate with other cavities (figure 6.12a). The largest ofthesearethesuperiorandinferior orbital fissures.Theyprovideopenings through which nerves and blood vessels communicatewiththeorbitorpasstotheface.Theopticnerve,forthesenseofvision,passesfromtheeyethroughtheoptic foramenandentersthecranialcavity.Thenasolacrimal(nā-zō-lak′ri-măl;nasus,nose+lacrima,tear)canal(seefigure6.11)passesfromtheorbitintothenasalcavity.Itcontainsaductthatcarriestearsfromtheeyestothenasalcavity.Asmalllacrimal(lak′ri-măl)bonecanbeseenintheorbitjustabovetheopeningofthiscanal.

Predict 4

Why does your nose run when you cry?

Thenasalcavityisdividedintorightandlefthalvesbyanasal septum(sep′tŭm;wall)(figure6.12a).Thebonypartofthenasalseptum consists primarily of the vomer (vō′mer) inferiorly andtheperpendicular plateoftheethmoid(eth′moyd;sieve-shaped)bonesuperiorly.Theanteriorpartofthenasalseptumisformedbycartilage. The external part of the nose is formed mostly of cartilage.Thebridgeofthenoseisformedbythenasal bones. Each of the lateral walls of the nasal cavity has three bonyshelves, called the nasal conchae (kon′kē; resembling a conchshell).Theinferiornasalconchaisaseparatebone,andthemiddleandsuperiorconchaeareprojectionsfromtheethmoidbone.Theconchaeincreasethesurfaceareainthenasalcavity.Theincreasedsurfaceareaoftheoverlyingepitheliumfacilitatesmoisteningandwarmingoftheairinhaledthroughthenose(seechapter15). Severalofthebonesassociatedwiththenasalcavityhavelargecavities within them, called the paranasal (par-ă-nā′săl; para,alongside) sinuses (figure6.13),whichopen into thenasal cavity.Thesinusesdecrease theweightof theskullandactasresonatingchambersduringvoiceproduction.Compareanormalvoicewiththevoiceofapersonwhohasacoldandwhosesinusesare“stoppedup.”Thesinusesarenamedfortheboneswheretheyarelocatedandincludethefrontal,maxillary,ethmoidal,andsphenoidalsinuses.



formingthefloorofthecranialcavity,fromanteriortoposterior,arethefrontal,ethmoid,sphenoid,temporal,andoccipitalbones.Several foramina can be seen in the floor of the middle fossa.These allow nerves and blood vessels to pass through the skull.Forexample,theforamenrotundumandforamenovaletransmitimportantnervestotheface.Amajorarterytothemeninges(themembranesaroundthebrain)passesthroughtheforamenspino-sum.Theinternalcarotidarterypassesthroughthecarotidcanal,andtheinternaljugularveinpassesthroughthejugularforamen(see chapter 13). The large foramen magnum, through whichthe spinal cord joins the brain, is located in the posterior fossa.

Theskullhasadditionalsinuses,calledthemastoid air cells,which are located inside the mastoid processes of the temporalbone.Theseaircellsopenintothemiddleearinsteadofintothenasalcavity.Anauditorytubeconnectsthemiddleeartothenaso-pharynx(upperpartofthroat).

Interior of the Cranial CavityWhenthefloorofthecranialcavityisviewedfromabovewiththeroofcutaway(figure6.14),itcanbedividedroughlyintothreecra-nialfossae(anterior,middle,andposterior),whichareformedasthedevelopingskullconformstotheshapeofthebrain.Thebones

Superior orbital fissure

Supraorbital foramen

Optic foramen

Coronal suture

Inferior orbital fissure

Infraorbital foramen

Mental foramen

Nasal cavity

Middle nasal concha

Sphenoid bone

Frontal bone

Parietal bone

Mandible

Orbit

Temporal bone

Nasal bone

Lacrimal bone

Zygomatic bone

Perpendicular plateof ethmoid bone

Vomer

Inferior nasal concha

Maxilla

Nasalseptum

Frontal view

Zygomaticbone

Maxilla

Frontal bone

Mandible

Nasal bone

(b)

(a)

Figure 6.12 Skull and Face (The names of bones are in bold.)(a)Frontalviewoftheskull.(b)Bonylandmarksoftheface.


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Ethmoidal sinus

Sphenoidal sinus

Maxillary sinus

Lateral view Anterior view

Sphenoid bone

Foramen rotundum

Internal auditory canal

Foramen magnum

Frontal sinuses

Crista galli

Cribriform plateEthmoid bone

Frontal bone

Optic foramen

Sella turcica

Foramen ovaleForamen spinosum Carotid canal

Jugular foramen

Parietal bone

Occipital bone

Superior view

Temporal bone

Hypoglossal canal

Anterior cranial fossa

Middle cranial fossa

Posterior cranial fossa

Figure 6.13 Paranasal Sinuses

(a) (b)

Figure 6.14 Floor of the Cranial Cavity (The names of bones are in bold.)theroofoftheskullhasbeenremoved,andthefloorisviewedfromabove.



palatine(pal′ă-tīn)bones.Theconnectivetissueandmusclesthatmakeupthesoft palateextendposteriorlyfromthehard,orbony,palate. The hard and soft palates separate the nasal cavity andnasopharynxfromthemouth,enablingustochewandbreatheatthesametime.

Hyoid BoneThehyoid bone(figure6.16)isanunpaired,U-shapedbone.Itisnotpartoftheskull(seetable6.1)andhasnodirectbonyattach-menttotheskull.Musclesandligamentsattachittotheskull.Thehyoidboneprovidesanattachmentforsometonguemuscles,andit isanattachmentpointforimportantneckmusclesthatelevatethelarynx(voicebox)duringspeechorswallowing.

VertebralcolumnThevertebral column,orbackbone,isthecentralaxisoftheskel-eton,extendingfromthebaseoftheskulltoslightlypasttheendofthepelvis.Inadults, itusuallyconsistsof26individualbones,grouped into five regions (figure 6.17; see table 6.1): 7 cervical(ser′vĭ-kal;neck)vertebrae(ver′tĕ-brē;verto,toturn),12thoracic(thō-ras′ik) vertebrae, 5 lumbar (lŭm′bar) vertebrae, 1 sacral(sā′krăl)bone,and1coccyx (kok′siks)bone.Theadultsacraland

Thecentralregionofthesphenoidboneismodifiedintoastruc-tureresemblingasaddle,thesella turcica(sel′ătŭr′sĭ-kă;Turkishsaddle),whichcontainsthepituitarygland.

Base of Skull Viewed from BelowManyof thesameforaminathatarevisible in the interiorof theskullcanalsobeseeninthebaseoftheskull,whenviewedfrombelow, with the mandible removed (figure 6.15). Other special-izedstructures,suchasprocessesformuscleattachments,canalsobe seen. The foramen magnum is located in the occipital bonenearthecenteroftheskullbase.Occipital condyles(ok-sip′i-tălkon′dīlz),thesmoothpointsofarticulationbetweentheskullandthevertebralcolumn,arelocatedbesidetheforamenmagnum. Two long, pointed styloid (stī′loyd; stylus or pen-shaped)processesprojectfromtheinferiorsurfaceofthetemporalbone.Themusclesinvolvedinmovingthetongue,thehyoidbone,andthepharynx(throat)originatefromthisprocess.Themandibular fossa,where themandiblearticulateswith the temporalbone, isanteriortothemastoidprocess. The hard palate (pal′ăt) forms the floor of the nasal cavityand the roof of the mouth. The anterior two-thirds of the hardpalate is formed by the maxillae, the posterior one-third by the

Figure 6.15 Base of the Skull as Viewed from Below (The names of bones are in bold.)themandiblehasbeenremoved.

Inferior orbital fissure

Foramen ovaleForamen spinosum

External auditory canal

Jugular foramen

Occipital condyle

Incisive fossa

Maxilla

Hard palate

Palatine process of maxillary bone

Horizontal plate of palatine bone

Vomer

Zygomatic bone

Styloid processMandibular fossaCarotid canal

Mastoid process

Temporal bone

Occipital bone

Foramen magnum

Sphenoid bone

Nuchal lines

Inferior view


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coccyxbonesfusefrom5and3–4individualbones,respectively.Forconvenience,eachofthefiveregionsisidentifiedbyaletter,andthevertebraewithineachregionarenumbered:C1–C7,T1–T12,L1–L5,S,andCO.Youcanrememberthenumberofvertebraeineachregionbyrememberingmealtimes:7,12,and5. The adult vertebral column has four major curvatures. Thecervical regioncurvesanteriorly, the thoracicregioncurvespos-teriorly, the lumbar region curves anteriorly, and the sacral andcoccygealregionstogethercurveposteriorly. Abnormalvertebralcurvaturesarenotuncommon.Kyphosis(kī-fō′sis)isanabnormalposteriorcurvatureofthespine,mostlyintheupperthoracicregion,resultinginahunchbackcondition.Lordosis (lōr-dō′sis; curving forward) is an abnormal anteriorcurvatureofthespine,mainlyinthelumbarregion,resultinginaswaybackcondition.Scoliosis(skō-lē-ō′sis)isanabnormallateralcurvatureofthespine. Thevertebralcolumnperformsthefollowingfivemajorfunc-tions:(1)supportstheweightoftheheadandtrunk;(2)protectsthespinalcord; (3)allowsspinalnerves toexit thespinalcord;(4)providesasiteformuscleattachment;and(5)permitsmove-mentoftheheadandtrunk.

General Plan of the VertebraeEach vertebra consists of a body, an arch, and various processes(figure6.18).Theweight-bearingportionofeachvertebra is thebody.Thevertebralbodiesareseparatedby intervertebral disks(seefigure6.17),whichareformedbyfibrocartilage.Thevertebral archsurroundsalargeopeningcalledthevertebral foramen.Thevertebral foraminaofall thevertebrae form thevertebral canal,where the spinal cord is located. The vertebral canal protectsthe spinal cord from injury. Each vertebral arch consists of two

Figure 6.16 Hyoid Bone

Figure 6.17 Vertebral Columncompletecolumnviewedfromtheleftside.

Body

Body

Anterior view

Lateral view(from the left side)

Cervicalregion(curvedanteriorly)

Thoracicregion(curvedposteriorly)

Lumbarregion(curvedanteriorly)

Sacral and coccygealregions(curvedposteriorly)

First cervical vertebra(atlas)

Second cervical vertebra(axis)

Seventh cervical vertebra

First thoracic vertebra

Intervertebral disk

Twelfth thoracic vertebra

Intervertebral foramina

First lumbar vertebra

Body

Transverse process

Spinous process

Fifth lumbar vertebra

Sacrum

Coccyx

Lateral view

Sacral promontory



pedicles(ped′ĭ-klz),whichextendfromthebodytothetransverseprocessofeachvertebra,andtwolaminae(lam′i-nē;thinplates),whichextendfromthetransverseprocessestothespinousprocess.Atransverse processextendslaterallyfromeachsideofthearch,between the pedicle and lamina, and a single spinous processprojectsdorsally fromwherethetwolaminaemeet.Thespinousprocessescanbeseenandfeltasaseriesoflumpsdownthemid-line of the back (see figure 6.24b). The transverse and spinousprocessesprovideattachmentsitesforthemusclesthatmovethevertebral column.Spinalnerves exit the spinal cord through theintervertebral foramina, which are formed by notches in thepediclesofadjacentvertebrae(seefigure6.17).Eachvertebrahasasuperiorandinferiorarticular processwherethevertebraearticu-late with each other. Each articular process has a smooth “littleface”calledanarticular facet(fas′et).

Regional Differences in VertebraeThe cervical vertebrae (figure 6.19a–c) have very small bodies,except for the atlas, which has no body. Because the cervicalvertebraearerelativelydelicateandhavesmallbodies,dislocations

Figure 6.18 Vertebra

Superior articular process

Articular facet

Transverse process

Vertebral foramen

Body

Pedicle

Lamina

Vertebral arch

Spinous process

Anterior

Superior view

Posterior

Superiorarticular facet

Spinous process

Transverseprocess

Transverseforamen

Vertebral foramen

Body

Pedicle

Lamina

Posterior arch

Atlas (first cervical vertebra), superior view

Thoracic vertebra, superior view

Lumbar vertebra, superior view

Cervical vertebra, superior view

Superior articularfacet (articulates with occipital condyle)

Facet for dens

Transverseprocess

Transverseforamen

Vertebral foramen

Anterior arch

Body

Spinous process

Transverseprocess

Vertebral foramen

Pedicle

Lamina


Facets for ribattachment


Spinous process

Transverseprocess

Vertebral foramenPedicle

Lamina

Body

Dens(articulateswith atlas)

Dens

Body

Axis (second cervical vertebra),superior view

Lateral view

Figure 6.19 Regional Differences in Vertebraetheposteriorportionliesatthetopofeachillustration.

(a)

(d)

(e)

(b)

(c)


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Vertebralcanal (sacralcanal)

Posteriorsacralforamina

Median sacralcrest

Sacral hiatus

Articular facet (articulates with fifth lumbar vertebra)

CoccyxCoccyx


Anteriorsacralforamina

Sacral promontory

Figure 6.20 Sacrum

(a) (b)

of thebodyof the first sacralvertebrabulges to form thesacral promontory (prom′on-tō-rē) (see figure 6.17), a landmark thatcanbefeltduringavaginalexamination.Itisusedasareferencepointtodetermineifthepelvicopeningsarelargeenoughtoallowfornormalvaginaldeliveryofababy. The coccyx, or tailbone, usually consists of four more-or-lessfusedvertebrae.Thevertebraeofthecoccyxdonothavethetypicalstructureofmostothervertebrae.Theyconsistofextremelyreducedvertebralbodies,without the foraminaorprocesses,usually fusedintoasinglebone.Thecoccyxiseasilybrokenwhenapersonfallsbysittingdownhardonasolidsurfaceorinwomenduringchildbirth.

ribcageTherib cage protectsthevitalorganswithinthethoraxandpre-ventsthecollapseofthethoraxduringrespiration.Itconsistsofthethoracicvertebrae,theribswiththeirassociatedcartilages,andthesternum(figure6.21).

acaSEinPoint

Rib Fractures

Han D. Mann’s ladder fell as he was working on his roof, and helandedontheladderwithhischest.threeribswerefracturedonhisright side. it was difficult for Han to cough, laugh, or even breathewithout severe pain in the right side of his chest.the middle ribsare those most commonly fractured, and the portion of each ribthat forms the lateral wall of the thorax is the weakest and mostcommonly broken.the pain from rib fractures occurs because thebroken ends move during respiration and other chest movements,stimulating pain receptors. Broken rib ends can damage internalorgans, such as the lungs, spleen, liver, and diaphragm. Fracturedribsarenotoftendislocated,butdislocatedribsmayhavetobesetforproperhealingtooccur.Bindingthechesttolimitmovementcanfacilitatehealingandlessenpain.

andfracturesaremorecommoninthisareathaninotherregionsof the vertebral column. Each of the transverse processes has atransverse foramen through which the vertebral arteries passtowardthebrain.Severalofthecervicalvertebraealsohavepartlysplitspinousprocesses.Thefirstcervicalvertebra(figure6.19a)iscalledtheatlasbecauseitholdsupthehead,asAtlasinclassicalmythology held up the world. Movement between the atlas andtheoccipitalboneisresponsiblefora“yes”motionofthehead.Italsoallowsaslighttiltingoftheheadfromsidetoside.Thesecondcervicalvertebra(figure6.19b)iscalledtheaxisbecauseaconsid-erableamountofrotationoccursatthisvertebra,asinshakingthehead“no.”Thisrotationoccursaroundaprocesscalledthedens(denz),whichprotrudessuperiorlyfromtheaxis. Thethoracic vertebrae(figure6.19d)possesslong,thinspinousprocesses thataredirected inferiorly.Thethoracicvertebraealsohaveextraarticular facetsontheir lateral surfaces thatarticulatewiththeribs. Thelumbar vertebrae(figure6.19e)havelarge,thickbodiesandheavy,rectangulartransverseandspinousprocesses.Becausethelumbarvertebraehavemassivebodiesandcarryalargeamountofweight,rupturedintervertebraldisksaremorecommoninthisareathaninotherregionsofthecolumn.Thesuperiorarticularfacetsofthelumbarvertebraefacemedially,whereastheinferiorarticularfacets face laterally. This arrangement tends to “lock” adjacentlumbarvertebraetogether,givingthelumbarpartofthevertebralcolumnmorestrength.Thearticularfacetsinotherregionsofthevertebral column have a more “open” position, allowing for morerotationalmovementbutlessstabilitythaninthelumbarregion. Thefivesacralvertebraearefusedintoasinglebonecalledthesacrum(figure6.20).Thespinousprocessesofthefirstfoursacralvertebraeformthemedian sacral crest.Thespinousprocessofthefifthvertebradoesnot form, leavingasacral hiatus (hī-ā-tŭs)attheinferiorendofthesacrum,whichisoftenthesiteof“caudal”anestheticinjectionsgivenjustbeforechildbirth.Theanterioredge



6.7 aPPEnDicularSKElEtonLearning Outcomes After reading this section, you should be able to

A. identifythebonesthatmakeupthepectoralgirdle,andrelatetheirstructureandarrangementtothefunctionofthegirdle.

B. nameanddescribethemajorbonesoftheupperlimb.C. nameanddescribethebonesofthepelvicgirdleandexplain

whythepelvicgirdleismorestablethanthepectoralgirdle.D. namethebonesthatmakeupthecoxalbone.Distinguish

betweenthemaleandfemalepelvis.e. identifyanddescribethebonesofthelowerlimb.

Theappendicular(ap′en-dik′ū-lăr;appendage)skeletonconsistsofthebonesoftheupperandlowerlimbs,aswellasthegirdles,whichattachthelimbstotheaxialskeleton.

PectoralGirdleThepectoral (pek′tō-răl)girdle,or shoulder girdle (figure6.22),consistsoffourbones,twoscapulaeandtwoclavicles,whichattachtheupper limbtothebody.Thescapula (skap′ū-lă),orshoulder blade, is a flat, triangular bone with three large fossae wheremusclesextendingtothearmareattached(figures6.23and6.24;see figure6.10).A fourth fossa, theglenoid (glen′oyd)cavity, iswheretheheadofthehumerusconnectstothescapula.Aridge,calledthespine,runsacrosstheposteriorsurfaceofthescapula.A projection, called the acromion (ă-krō′mē-on; akron, tip +omos,shoulder)process,extendsfromthescapularspinetoformthe point of the shoulder. The clavicle (klav′i-kl), or collarbone,articulateswiththescapulaattheacromionprocess.Theproximalendoftheclavicleisattachedtothesternum,providingtheonly

Ribs and Costal CartilagesThe 12 pairs of ribs can be divided into true ribs and false ribs.Thetrue ribs,ribs1–7,attachdirectlytothesternumbymeansofcostalcartilages.Thefalse ribs, ribs8–12,donotattachdirectlyto the sternum. Ribs 8–10 attach to the sternum by a commoncartilage;ribs11and12donotattachatalltothesternumandarecalledfloating ribs.

SternumThe sternum (ster′nŭm), or breastbone (figure 6.21), is dividedinto three parts: the manubrium (mă-nū′brē-ŭm; handle), thebody,andthexiphoid(zif′oyd,zī′foyd;sword)process.Thester-numresemblesasword,withthemanubriumformingthehandle,thebodyformingtheblade,andthexiphoidprocessformingthetip. At the superior end of the sternum, a depression called thejugular notch is locatedbetweentheendsof theclavicleswherethey articulate with the sternum. A slight elevation, called thesternal angle, can be felt at the junction of the manubrium andthebodyofthesternum.Thisjunctionisanimportantlandmarkbecauseitidentifiesthelocationofthesecondrib.Thisidentifica-tionallowstheribstobecounted;forexample,itcanhelpahealthprofessionallocatetheapexoftheheart,whichisbetweenthefifthandsixthribs. The xiphoid process is another important landmark of thesternum.Duringcardiopulmonaryresuscitation(CPR), it isveryimportanttoplacethehandsoverthebodyofthesternumratherthan over the xiphoid process. Pressure applied to the xiphoidprocesscandriveitintoanunderlyingabdominalorgan,suchastheliver,causinginternalbleeding.

Clavicle

Jugular notch

Seventh cervical vertebra

First thoracic vertebra

True ribs(1–7)

Costal cartilage

False ribs(8–12)

Manubrium

Body

Xiphoid process

Sternum

Floating ribs

1

2

3

4

5

6

7

8

9

10

11

12

Anterior view

L1

T12

Sternal angle

Figure 6.21 Rib Cage


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neck,locatedattheproximalendofthehumeralshaft.Lateraltotheheadaretwotubercles,agreater tubercleandalesser tubercle.Musclesoriginatingonthescapulaattachtothegreaterandlessertubercles and hold the humerus to the scapula. Approximatelyone-thirdofthewaydowntheshaftofthehumerus,onthelateralsurface,isthedeltoid tuberosity,wherethedeltoidmuscleattaches.Thesizeofthedeltoidtuberositycanincreaseastheresultoffre-quentandpowerfulpullsfromthedeltoidmuscle.Forexample,inbodybuilders,thedeltoidmuscleandthedeltoidtuberosityenlargesubstantially.Anthropologists,examiningancienthumanremains,canuse thepresenceofenlargeddeltoid tuberositiesasevidencethatapersonwasengagedinliftingheavyobjectsduringlife.Ifthehumerusofapersonexhibitsanunusuallylargedeltoidtuberosityforherage,itmayindicate,insomesocieties,thatshewasaslaveandwasrequiredtoliftheavyloads.Thedistalendofthehumerusis modified into specialized condyles that connect the humerusto the forearm bones. Epicondyles (ep′i-kon′dīlz; epi, upon) onthedistalendofthehumerus,justlateraltothecondyles,provideattachmentsitesforforearmmuscles.

ForearmTheforearmhastwobones:theulna(ŭl′nă)onthemedial(littlefinger)sideoftheforearmandtheradiusonthelateral(thumb)side(figure6.26).Theproximalendoftheulnaformsatrochlear notchthatfitstightlyovertheendofthehumerus,formingmostoftheelbowjoint.Justproximaltothetrochlearnotchisanextensionof the ulna, called the olecranon (ō-lek′ră-non; elbow) process,whichcanbefeltasthepointoftheelbow(seefigure6.28).Justdistaltothetrochlearnotchisacoronoid(kōr′ŏ-noyd)process,whichhelpscompletethe“grip”oftheulnaonthedistalendofthehumerus.Thedistalendoftheulnaformsahead,whicharticulateswiththebonesofthewrist,andastyloid processislocatedonitsmedialside.Theulnarheadcanbeseenasaprominentlumpontheposteriorulnarsideofthewrist.Theproximalendoftheradiushasaheadbywhichtheradiusarticulateswithboththehumerusandtheulna.Theradiusdoesnotattachasfirmlytothehumerusastheulna does. The radial head rotates against the humerus and ulna.Just distal to the radial head is a radial tuberosity, where one ofthearmmuscles,thebicepsbrachii,attaches.Thedistalendoftheradiusarticulateswiththewristbones.Astyloidprocessislocatedonthelateralsideofthedistalendoftheradius.Theradialandulnarstyloidprocessesprovideattachmentsitesforligamentsofthewrist.

WristThe wrist is a relatively short region between the forearm andthe hand; it is composed of eight carpal (kar′păl; wrist) bones(figure6.27).Theseeightbonesarethescaphoid(skaf′oyd),lunate(lū′nāt), triquetrum(trī-kwē′trŭm),pisiform(pis′i-fōrm), trape-zium(tra-pē′zē-ŭm),trapezoid(trap′ĕ-zoyd),capitate(kap′i-tāt),andhamate(ha′māt).Thecarpalbonesarearrangedintworowsof four bones each and form a slight curvature that is concaveanteriorlyandconvexposteriorly.Anumberofmnemonicshavebeendevelopedtohelpstudentsrememberthecarpalbones.Thefollowing one allows students to remember them in order fromlateral to medial for the proximal row (top) and from medial tolateral(bythethumb)forthedistalrow:SoLongTopPart,HereComes The Thumb—that is, Scaphoid, Lunate, Triquetrum,Pisiform,Hamate,Capitate,Trapezoid,andTrapezium.

bonyattachmentofthescapulatotheremainderoftheskeleton.Theclavicleisthefirstbonetobeginossificationinthefetus.Thisrelatively brittle bone may be fractured in the newborn duringdelivery.Theboneremainsslenderinchildrenandmaybebrokenasachildattemptstotaketheimpactofafallonanoutstretchedhand.Theclavicleisthickerinadultsandislessvulnerabletofrac-ture.Eventhoughitisthefirstbonetobeginossification,itisthelast to complete ossification. The coracoid (kōr′ă-koyd) processcurvesbelowtheclavicleandprovidesfortheattachmentofarmandchestmuscles.

upperlimbTheupper limbconsistsof thebonesof thearm, forearm,wrist,andhand(seefigure6.22).

ArmThe arm is the region between the shoulder and the elbow; itcontains the humerus (hū′mer-ŭs; shoulder) (figure 6.25). Theproximalendofthehumerushasasmooth,roundedhead,whichattachesthehumerustothescapulaattheglenoidcavity.Aroundthe edge of the humeral head is the anatomical neck. When thejointneedstobesurgicallyreplaced,thisneckisnoteasilyacces-sible.Amoreaccessiblesiteforsurgicalremovalisatthesurgical

Upper limb

Pectoral girdle

Phalanges

Anterior view

Metacarpal bones

Clavicle

Scapula

Humerus

Radius

Ulna

Carpal bones

Figure 6.22 Bones of the Pectoral Girdle and Right Upper Limb



Spine of scapula

Supraspinous fossa of scapula

Acromion processof scapula

Distal end of clavicle

Coracoid processof scapula

Body of clavicle

Posterior

Anterior

Distal end

Proximal end

Posterior view

Acromion process

Glenoid cavity

Lateral border

Coracoid process

Subscapularfossa

Medial border

Viewin (d)

Inferior angle

Spine

Supraspinousfossa

Coracoid processAcromion process

Glenoid cavity

Infraspinous fossa

Lateral border

Anterior view

Superior viewSuperior view

Body of clavicle

Figure 6.23 Right Scapula and Clavicle(a)rightscapula,anteriorview.(b)rightscapula,posteriorview.(c)rightclavicle,superiorview.(d)Photographoftherightscapulaandclaviclefromasuperiorview,showingtherelationshipbetweenthedistalendoftheclavicleandtheacromionprocessofthescapula.

(a)

(c) (d)

(b)

Skeletal

the bones and ligaments ontheanteriorsideofthewristformacarpal tunnel, which does not have much“give.”tendonsandnervespassfromtheforearmthroughthecarpaltunneltothehand.Fluidand connective tissue can accumulate inthe carpal tunnel as a result of inflamma-tionassociatedwithoveruseortrauma.theinflammationcanalsocausethetendonsin

the carpal tunnel to enlarge.the accumu-latedfluidandenlargedtendonscanapplypressuretoamajornervepassingthroughthe tunnel. the pressure on this nervecausescarpal tunnel syndrome,character-izedbytingling,burning,andnumbnessinthehand. treatments for carpal tunnel syndromevary, depending on the severity of the

syndrome. Mild cases can be treated non-surgically with either anti-inflammatorymedicationsorstretchingexercises.However,if symptoms have lasted for more than6months, surgery is recommended.Surgicaltechniques involve cutting the carpal liga-menttoenlargethecarpaltunnelandeasepressureonthenerve.

CLINICALIMPACT Carpal Tunnel Syndrome


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Sternum

Clavicle

Distal end of clavicle

Acromionprocess

Jugular notch

Head

Anatomical neckLesser tubercle

Surgical neck

Olecranon fossa

Greater tubercle

Deltoid tuberosity

Lateral epicondyle

CondylesCapitulum

Trochlea

Medial epicondyle


Trochlea

Lateral epicondyle

Greater tubercle

Spinous process ofseventh cervical vertebra

Lumbar spinousprocesses

Superior borderof scapula

Scapula

Medial borderof scapula

Inferior angleof scapula

Spine of scapula

Figure 6.24 Surface Anatomy of the Pectoral Girdle and Thoracic Cage(a)Bonesofthepectoralgirdleandtheanteriorthorax.(b)Bonesofthescapulaandtheposteriorvertebralcolumn.

Figure 6.25 Right Humerus

(a)

(a)

(b)

(b)



Carpal bones(distalrow)

Radius

TrapezoidTrapezium

Proximalphalanx of thumb

Proximal phalanx of finger

Middle phalanx of finger

Distal phalanx of finger

Posterior view

Ulna

CapitateHamate

1

2345

Digits

Metacarpalbones

Distalphalanxof thumb

Carpalbones(proximalrow)

LunateScaphoid

TriquetrumPisiform

Heads ofmetacarpal

bones(knuckles)

Olecranonprocess

Headof ulna

Acromionprocess

Medial border of scapula

Olecranonprocess

HandFivemetacarpal(met′ă-kar′păl)bonesareattachedtothecarpalbonesandformthebonyframeworkofthehand(figure6.27).Themetacarpalbonesarealignedwiththefivedigits:thethumbandfingers. They are numbered 1 to 5, from the thumb to the littlefinger.Theends,orheads,ofthefivemetacarpalbonesassociatedwiththethumbandfingersformtheknuckles(figure6.28).Eachfinger consistsof three smallbones called phalanges (fă-lan′jēz;sing.phalanx,fā′langks),namedaftertheGreekphalanx,awedgeof soldiers holding their spears, tips outward, in front of them.The phalanges of each finger are called proximal, middle, anddistal,accordingtotheirpositioninthedigit.Thethumbhastwophalanges,proximalanddistal.Thedigitsarealsonumbered1to5,startingfromthethumb.

PelvicGirdleThepelvic girdleistheplacewherethelowerlimbsattachtothebody(figure6.29).Therightandleftcoxal(kok′sul)bones,orhipbones, join each other anteriorly and the sacrum posteriorly toformaringofbonecalled thepelvic girdle.Thepelvis (pel′vis;

Olecranon process

Head

Radial tuberosity

Radius(shaft)

Styloid process

Anterior view

Trochlear notchCoronoid process

Ulna(shaft)

Head

Styloid process

Superior view

Head of radius

Olecranonprocess

Coronoid process

Trochlearnotch

Figure 6.26 Right Ulna and Radius(a)anteriorviewoftherightulnaandradius.(b)Proximalendsoftherightulnaandradius.

(a)

(b)

Figure 6.27 Bones of the Right Wrist and Hand

Figure 6.28 Surface Anatomy Showing Bones of the Pectoral Girdle and Upper Limb


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crest can be seen along the superior margin of each ilium, andan anterior superior iliac spine, an important hip landmark, islocatedattheanteriorendoftheiliaccrest.Thecoxalbonesjoineachotheranteriorlyatthepubic(pū′bik)symphysisandjointhesacrum posteriorly at the sacroiliac (sā-krō-il′ē-ak) joints (seefigure6.30).Theacetabulum(as-ĕ-tab′ū-lŭm;vinegarcup)isthesocketofthehipjoint.Theobturator(ob′too-rā-tŏr)foramenisthelargeholeineachcoxalbonethatisclosedoffbymusclesandotherstructures. Themalepelviscanbedistinguishedfromthefemalepelvisbecauseitisusuallylargerandmoremassive,butthefemalepelvistendstobebroader(figure6.32;table6.3).Boththeinletandtheoutletofthefemalepelvisarelargerthanthoseofthemalepelvis,and the subpubic angle is greater in the female (figure 6.32a,b).Theincreasedsizeoftheseopeningshelpsaccommodatethefetus

basin)includesthepelvicgirdleandthecoccyx(figure6.30).Thesacrumandcoccyxformpartofthepelvisbutarealsopartoftheaxialskeleton.Eachcoxalboneisformedbythreebonesfusedtooneanotherto formasinglebone(figure6.31).The ilium (il′ē-ŭm) is themostsuperior, the ischium (is′kē-ŭm) is inferiorandposterior,andthepubis(pū′bis)isinferiorandanterior.Aniliac

Coxal boneSacrum

Femur

Patella

Lower limb

Pelvic girdle

Tibia

Fibula

Tarsal bonesMetatarsalbonesPhalanges

Anterior view

Sacroiliac joint

Anterior superioriliac spine

Acetabulum

Coccyx

Iliac crest

Obturatorforamen

Subpubic angle

Anterosuperior view

Ischium

Pubis

Ilium

Sacrum

Coxalbone

Pubic symphysis

Sacral promontory

Figure 6.29 Bones of the Pelvic Girdle and Right Lower Limb

Figure 6.30 Pelvis

TABle 6.3 Differences Between Male and Female Pelvic Girdles

Area Description of DifferenceGeneral Femalepelvissomewhatlighterinweightand

widerlaterallybutshortersuperiorlyto inferiorlyandlessfunnel-shaped;lessobvious muscleattachmentpointsinfemalethaninmale

Sacrum Broaderinfemale,withtheinferiorportion directedmoreposteriorly;thesacralpromontory projectslessanteriorlyinfemale

Pelvicinlet Heart-shapedinmale;ovalinfemale

Pelvicoutlet Broaderandmoreshallowinfemale

Subpubicangle lessthan90degreesinmale;90degreesormore infemale

ilium Moreshallowandflaredlaterallyinfemale

ischialspines Fartherapartinfemale

ischialtuberosities turnedlaterallyinfemaleandmediallyinmale (notshowninfigure6.32)



Iliac crest

Greatersciatic notch

Ischial spine

Ischial tuberosityLateral view Medial view

Obturator foramen

Pubic symphysis

Acetabulum

Ilium

Pubis

Pelvic brim

Articular surface(area ofarticulationwith sacrum)

Greater sciatic notch

Ischium

Ischial spine

Ischium

Iliac fossa

Coccyx

Pubicsymphysis

Ischialspine

Sacral promontory

Subpubic angle

Pelvicbrim

Pelvicinlet(reddashedline)

Pubicsymphysis

Pelvicoutlet(bluedashedline)

Male Female

(a) Anterosuperior view (b) Anterosuperior view

Pelvic inlet

Pelvicbrim

Coccyx

Sacral promontory

Pelvic outlet

(c) Medial view

Figure 6.31 Right Coxal Bone

Figure 6.32 Comparison of the Male Pelvis to the Female Pelvis(a)inamale,thepelvicinlet(red dashed line)andoutlet(blue dashed line)aresmall,andthesubpubicangleislessthan90degrees.(b)inafemale,thepelvicinlet(red dashed line)andoutlet(blue dashed line)arelarger,andthesubpubicangleis90degreesorgreater.(c)amidsagittalsectionthroughthepelvisshowsthepelvicinlet(red arrowandred dashed line)andthepelvicoutlet(blue arrowandblue dashed line).

(a) (b)


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aredamaged.Ifthisoccurs,thefemoralheadmaydegeneratefromlackofnourishment.Thetrochantersarepointsofmuscleattach-ment.Thepatella(pa-tel′ă),orkneecap(figure6.33b), is locatedwithinthemajortendonoftheanteriorthighmusclesandenablesthetendontobendovertheknee.

LegThelegistheregionbetweenthekneeandtheankle(figure6.34).Itcontainstwobones,calledthetibia(tib′ē-ă;shinbone)andthefibula(fib′ū-lă).Thetibiaisthelargerofthetwoandisthemajorweight-bearingboneoftheleg.Theroundedcondylesofthefemurrestontheflatcondylesontheproximalendofthetibia.Justdis-taltothecondylesofthetibia,onitsanteriorsurface,isthetibial tuberosity, where the muscles of the anterior thigh attach. Thefibuladoesnotarticulatewiththefemur,butitsheadisattachedtotheproximalendofthetibia.Thedistalendsofthetibiaandfibula form a partial socket that articulates with a bone of theankle(thetalus).Aprominencecanbeseenoneachsideoftheankle(figure6.34).Thesearethemedial malleolus(mal-ē′ō-lŭs)ofthetibiaandthelateral malleolusofthefibula.

during childbirth. The pelvic inlet is formed by the pelvic brimand the sacralpromontory.The pelvic outlet isboundedby theischialspines,thepubicsymphysis,andthecoccyx(figure6.32c).

lowerlimbThelowerlimbconsistsofthebonesofthethigh,leg,ankle,andfoot(seefigure6.29).

ThighThethighistheregionbetweenthehipandtheknee(figure6.33a).Itcontainsasinglebonecalledthefemur.Theheadofthefemurarticulateswiththeacetabulumofthecoxalbone.Atthedistalendofthefemur,thecondylesarticulatewiththetibia.Epicondyles,locatedmedialandlateraltothecondyles,arepointsofligamentattachment. The femur can be distinguished from the humerusby its long neck, located between the head and the trochanters(trō′kan-terz). A “broken hip” is usually a break of the femoralneck.Abrokenhipisdifficulttorepairandoftenrequirespinningtoholdthefemoralheadtotheshaft.Amajorcomplicationcanoccurifthebloodvesselsbetweenthefemoralheadandtheacetabulum

Head

Neck

Greater trochanter

Lateral epicondyleLateral condyle

Body (shaft) of femur

Head

Neck

Medialepicondyle

Greater trochanter

Lateral epicondyle

Medialcondyle

Patellar groove

Linea aspera

Intercondylar fossa

Lesser trochanter

Anteriorsurface

Anterior view

Anterior view

Posterior view

Figure 6.33 Bones of the Thigh(a)rightfemur.(b)Patella.

(a)

(b)



AnkleThe ankle consists of seven tarsal (tar′săl; the sole of the foot)bones (figure 6.35). The tarsal bones are the talus (tā′lŭs; anklebone), calcaneus (kal-kā′nē-ŭs; heel), cuboid (kū′boyd), andnavicular(nă-vik′yū-lăr),andthemedial,intermediate,andlateralcuneiforms (kū′nē-i-fōrmz). The talus articulates with the tibiaand fibula to form the ankle joint, and the calcaneus forms theheel(figure6.36).AmnemonicforthedistalrowisMILC—thatis,Medial,Intermediate,andLateralcuneiformsandtheCuboid.AmnemonicfortheproximalthreebonesisNoThanksCow—thatis,Navicular,Talus,andCalcaneus.

FootThe metatarsal (met′ă-tar′săl) bones and phalanges of the footarearrangedandnumberedinamannerverysimilartothemeta-carpal bones and phalanges of the hand (see figure 6.35). Themetatarsalbonesaresomewhatlongerthanthemetacarpalbones,whereas the phalanges of the foot are considerably shorter thanthoseofthehand. There are three primary arches in the foot, formed by thepositions of the tarsal bones and metatarsal bones, and held inplacebyligaments.Twolongitudinalarchesextendfromtheheeltotheballofthefoot,andatransversearchextendsacrossthefoot.Thearchesfunctionsimilarlytothespringsofacar,allowingthefoottogiveandspringback.

Lateral condyle

Head

Medial condyle

Tibial tuberosity

TibiaFibula

Lateral malleolus

Anterior view

Medial malleolus

Cuboid

Lateral cuneiform

Metatarsalbones

Proximal phalanx

Middle phalanxDistal phalanx

Calcaneus

Talus

Navicular

Intermediate cuneiform

Medial cuneiform

Proximal phalanxof great toe

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Tarsal bones

Digits

Navicular

Cuboid

Fibula

Talus

Calcaneus

Tarsal bones

Tibia

Metatarsal bonesDistal phalanxof great toe

Superior view Medial view

Phalanges

Figure 6.34 Bones of the Legtherighttibiaandfibulaareshown.

Figure 6.35 Bones of the Right Foot

(a) (b)


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(fon′tă-nelz′),orsoftspots(figure6.37).Theyallowflexibilityinthe skullduring thebirthprocess, aswell asgrowthof theheadafter birth. Syndesmoses (sin′dez-mō′sēz) are fibrous joints inwhichthebonesareseparatedbysomedistanceandheldtogetherby ligaments. An example is the fibrous membrane connectingmostofthedistalpartsoftheradiusandulna.Gomphoses(gom-fō′sēz)consistofpegsfittedintosocketsandheldinplacebyliga-ments.Thejointbetweenatoothanditssocketisagomphosis.

cartilaginousJointsCartilaginous joints unite two bones by means of cartilage. Onlyslightmovementcanoccuratthesejoints.Examplesarethecartilageintheepiphysealplatesofgrowinglongbonesandthecartilages

6.8 JointSLearning Outcomes After reading this section, you should be able to

A. Describethetwosystemsforclassifyingjoints.B. Explainthestructureofafibrousjoint,listthethreetypes,and

giveexamplesofeachtype.C. Giveexamplesofcartilaginousjoints.D. illustratethestructureofasynovialjointandexplaintheroles

ofthecomponentsofasynovialjoint.e. classifysynovialjointsbasedontheshapeofthebonesinthe

jointandgiveanexampleofeachtype.F. Demonstratethedifferencebetweenthefollowingpairs

ofmovements:flexionandextension;plantarflexionanddorsiflexion;abductionandadduction;supinationandpronation;elevationanddepression;protractionandretraction;oppositionandreposition;inversionandeversion.

A joint, or an articulation, is a place where two bones cometogether. A joint is usually considered movable, but that is notalwaysthecase.Manyjointsexhibitlimitedmovement,andothersarecompletely,oralmostcompletely,immovable. Onemethodofclassifyingjointsisafunctionalclassification.Basedonthedegreeofmotion,ajointmaybecalledasynarthrosis(sin′ar-thrō′sis;nonmovablejoint),anamphiarthrosis(am′fi-ar-thrō′sis; slightly movable joint), or a diarthrosis (dī-ar-thrō′sis;freelymovable joint).However, functionalclassificationissome-what restrictive and is not used in this text. Instead, we use astructuralclassificationwherebyjointsareclassifiedaccordingtothe type of connective tissue that binds the bones together andwhetherthereisafluid-filledjointcapsule.Thethreemajorstruc-turalclassesofjointsarefibrous,cartilaginous,andsynovial.

FibrousJointsFibrous joints consist of two bones that are united by fibroustissueandthatexhibitlittleornomovement.Jointsinthisgroupare further subdivided on the basis of structure as sutures, syn-desmoses,orgomphoses.Sutures (soo′choorz)arefibrous jointsbetween the bones of the skull (see figure 6.11). In a newborn,somepartsofthesuturesarequitewideandarecalledfontanels

Lateralmalleolus

Patella

Tibial tuberosity

Anterior crestof tibia

Medial malleolus

Head of fibula

Calcaneus

Medial epicondyle of femur

Lateral epicondyleof femur

Parietalbone

Occipitalbone

Mastoid (posterolateral) fontanel

Lateral view

Superior view

Frontalbone

Sphenoidal(anterolateral)fontanel

Temporal bone

Squamoussuture

Lambdoidsuture

Coronalsuture

Frontal bones(not yet fusedinto a single bone)

Frontal(anterior)fontanel

Parietalbone

Occipital(posterior)fontanelOccipital

bone

Sagittalsuture

Figure 6.36 Surface Anatomy Showing Bones of the Lower Limb

Figure 6.37 Fetal Skull Showing Fontanels and Sutures

(a)

(b)



(ber′să; pocket). Bursae are located between structures that rubtogether,suchaswhereatendoncrossesabone;theyreducefric-tion,whichcoulddamagethestructuresinvolved.Inflammationofabursa,oftenresultingfromabrasion,iscalledbursitis.Asynovialmembrane may extend as a tendon sheath along some tendonsassociatedwithjoints(figure6.38).

Types of Synovial JointsSynovialjointsareclassifiedaccordingtotheshapeoftheadjoiningarticularsurfaces(figure6.39).Plane joints,orgliding joints,consistof two opposed flat surfaces that glide over each other. Examplesof these joints are the articular facets between vertebrae. Saddle joints consist of two saddle-shaped articulating surfaces orientedatrightanglestoeachother.Movementinthesejointscanoccurintwoplanes.Thejointbetweenthemetacarpalboneandthecarpalbone(trapezium)ofthethumbisasaddlejoint.Hinge jointspermitmovementinoneplaneonly.Theyconsistofaconvexcylinderofoneboneapplied toacorrespondingconcavityof theotherbone.Examples are the elbow and knee joints (figure 6.40a,b). The flatcondylarsurfaceofthekneejointismodifiedintoaconcavesurfacebyshock-absorbing fibrocartilagepadscalledmenisci (mĕ-nis′sī).Pivot jointsrestrictmovementtorotationaroundasingleaxis.Eachpivotjointconsistsofacylindricalbonyprocessthatrotateswithinaringcomposedpartlyofboneandpartlyofligament.Therotationthatoccursbetweentheaxisandatlaswhenshakingthehead“no”isanexample.Thearticulationbetweentheproximalendsoftheulnaandradiusisalsoapivotjoint.

betweentheribsandthesternum.Thecartilageofsomecartilaginousjoints,wheremuchstrainisplacedonthejoint,maybereinforcedbyadditionalcollagenfibers.Thistypeofcartilage,calledfibrocartilage(seechapter4),formsjointssuchastheintervertebraldisks.

SynovialJointsSynovial(si-nō′vē-ăl)jointsarefreelymovablejointsthatcontainfluidinacavitysurroundingtheendsofarticulatingbones.Mostjointsthatunitethebonesoftheappendicularskeletonaresyno-vialjoints,whereasmanyofthejointsthatunitethebonesoftheaxialskeletonarenot.Thispatternreflectsthegreatermobilityoftheappendicularskeletoncomparedtothatoftheaxialskeleton. Severalfeaturesofsynovialjointsareimportanttotheirfunc-tion(figure6.38).Thearticularsurfacesofboneswithinsynovialjointsarecoveredwitha thin layerofarticular cartilage,whichprovidesasmoothsurfacewherethebonesmeet.Thejoint cavityisfilledwithfluid.Thecavityisenclosedbyajoint capsule,whichhelpsholdthebonestogetherandallowsformovement.Portionsofthefibrouspartofthejointcapsulemaybethickenedtoformligaments. In addition, ligaments and tendons outside the jointcapsulecontributetothestrengthofthejoint. A synovial membrane lines the joint cavity everywhereexcept over the articular cartilage. The membrane producessynovial fluid, which is a complex mixture of polysaccharides,proteins,lipids,andcells.Synovialfluidformsathin,lubricatingfilmcovering the surfaces of the joint. In certain synovial joints, thesynovialmembranemayextendasapocket,orsac,calledabursa

Bursa

Joint cavity (filledwith synovial fluid)

Articularcartilage

Tendonsheath

Tendon

Bone

Bone

Blood vesselNerve

Synovial membrane

Fibrous part of joint capsule

Jointcapsule

Outer layer

Inner layerPeriosteum

Figure 6.38 Structure of a Synovial Joint


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Class and Example of JointPlane

SlightAcromion process of scapula and clavicleCarpals and metacarpals 2–5Ribs and vertebraeBetween carpal bonesBetween metatarsal bonesBetween tarsal bonesBetween articular processes of adjacent vertebrae

(complex joint with several planes and synchondroses)

Acromioclavicular

Two axes

SlightSlight

Carpometacarpal

CostovertebralIntercarpalIntermetatarsalIntertarsalIntervertebral

Sacroiliac

Tarsometatarsal

Multiple axes as a groupSlightSlightSlightSlightSlight

Slight

Slight

SaddleCarpometacarpal pollicisIntercarpalSternoclavicular

Carpal and metacarpal of thumbBetween carpal bonesManubrium of sternum and clavicle

HingeCubital (elbow)KneeInterphalangealTalocrural (ankle)

Humerus, ulna, and radiusFemur and tibiaBetween phalangesTalus, tibia, and fibula

One axisOne axisOne axisMultiple axes; one predominates

PivotMedial atlantoaxialProximal radioulnarDistal radioulnar

Atlas and axisRadius and ulnaRadius and ulna

RotationRotationRotation

Ball-and-SocketCoxal (hip)Humeral (shoulder)

Coxal bone and femurScapula and humerus

Multiple axesMultiple axes

EllipsoidAtlantooccipitalMetacarpopha- langeal (knuckles)Metatarsopha- langeal (ball of foot)Radiocarpal (wrist)Temporomandibular

Atlas and occipital boneMetacarpal bones and phalangesMetatarsal bones and phalangesRadius and carpal bonesMandible and temporal bone

Two axesTwo axes

Two axes

Multiple axesMultiple axes; one predominates

Ball-and-socket

Ellipsoid

Plane

Saddle

Hinge

Pivot

Structures Joined Movement

Between sacrum and coxal bone

Tarsal bones and metatarsal bones

Figure 6.39 Types of Synovial Joints



type of movement, whereas others permit movement in severaldirections.All themovementsaredescribedrelative to theana-tomicalposition.Becausemostmovementsareaccompaniedbymovementsintheoppositedirection,theyareoftenillustratedinpairs(figure6.41). Flexion and extension are common opposing movementsthatmaybedefinedinanumberofways,althougheachdefinitionhasanexception.Theliteraldefinitionsaretobend(flex)andtostraighten (extend). But we have chosen to use definitions withmoreutilityandfewerexceptions.Thus,wesaythatflexionmovesapartofthebodyintheanteriordirectionfromthefrontalplane,whereas extension moves a part in the posterior direction fromthefrontalplane(figure6.41a,b).Anexceptionistheknee,whereflexionmovestheleginaposteriordirectionandextensionmovesitinananteriordirection.

Ball-and-socket joints consistofaball (head)at theendofoneboneandasocket inanadjacentbone intowhichaportionof the ball fits. This type of joint allows a wide range of move-mentinalmostanydirection.Examplesaretheshoulderandhipjoints (figure 6.40c,d). Ellipsoid (ē-lip′soyd) joints, orcondyloid(kon′di-loyd) joints, are elongated ball-and-socket joints. Theshapeofthejointlimitsitsrangeofmovementnearlytothatofahingemotion,but intwoplanes.Examplesofellipsoid jointsarethejointbetweentheoccipitalcondylesoftheskullandtheatlasofthevertebralcolumnandthejointsbetweenthemetacarpalbonesandphalanges.

typesofMovementThetypesofmovementoccurringatagiven jointarerelated tothe structure of that joint. Some joints are limited to only one

Elbow

Humerus

Fat pad

Olecranon bursa

Trochlea

Articular cartilage of the trochlear notch

Joint capsule

Joint cavity

Synovial membrane

Articular cartilage

Coronoid process

Ulna

Femur

Articularcartilage

Meniscus

Tibia

Quadricepsfemoristendon

Suprapatellarbursa

Subcutaneousprepatellarbursa

Patella

Fat padPatellarligamentDeepinfrapatellarbursa

Knee

Pelvic bone

Articular cartilage

Joint cavity

Ligamentum teres

Head of femur

Neck of femur

Joint capsule

Greatertrochanter

Lessertrochanter

Femur

Hip

Subacromial bursa

Joint cavity

Acromion process (articular surface)

Articular cartilage over head of humerus

Scapula (cut surface)

Joint capsule

Articular cartilageover glenoid cavity

Shoulder

Tendon sheath on tendon of long head of biceps brachii

Biceps brachiitendon

Humerus

Biceps brachiimuscle

Sagittal sectionSagittal section

Frontal section Frontal section

Figure 6.40 Examples of Synovial Joints(a)Elbow.(b)Knee.(c)Shoulder.(d)Hip.

(a)

(c)

(b)

(d)


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Flexion

Extension

Pronation

Supination

Medial rotation Lateral rotation

Circumduction

Anterior tofrontal plane

Posterior tofrontal plane

Flexion Extension

Frontal plane

Abduction

Abduction

Adduction

(a)

(d)

(e) (f)

(b) (c)

Figure 6.41 Types of Movement(a)Flexionandextensionoftheelbow.(b)Flexionandextensionoftheneck.(c)abductionandadductionofthefingers.(d)Pronationandsupinationofthehand.(e)Medialandlateralrotationofthearm.(f )circumductionofthearm.



• Depressionismovementofastructureinaninferiordirection.Openingthemouthinvolvesdepressionofthemandible.

• Excursionismovementofastructuretooneside,asinmovingthemandiblefromsidetoside.

• Oppositionisamovementuniquetothethumbandlittlefinger.Itoccurswhenthetipsofthethumbandlittlefingerarebroughttowardeachotheracrossthepalmofthehand.Thethumbcanalsoopposetheotherdigits.

• Repositionreturnsthedigitstotheanatomicalposition.

Mostmovementsthatoccurinthecourseofnormalactivitiesare combinations of movements. A complex movement can bedescribedbynamingtheindividualmovementsinvolved. Whenthebonesofajointareforcefullypulledapartandtheligamentsaround the jointarepulledor torn,a sprain results.Aseparation exists when the bones remain apart after injury to ajoint.Adislocationiswhentheendofoneboneispulledoutofthesocketinaball-and-socket,ellipsoid,orpivotjoint. Hyperextension is usually defined as an abnormal, forcedextensionofajointbeyonditsnormalrangeofmotion.Forexample,if a person falls and attempts to break the fall by putting out ahand, the force of the fall directed into the hand and wrist maycause hyperextension of the wrist, which may result in sprainedjointsorbrokenbones.Somehealthprofessionals,however,definehyperextension as the normal movement of a structure into thespaceposteriortotheanatomicalposition.

Predict 5

What combination of movements at the shoulder and elbow joints allows a person to perform a crawl stroke in swimming?

6.9 EFFEctSoFaGinGontHESKElEtalSYStEManDJointS


A. Describetheeffectsofagingonbonesandjoints.

Themostsignificantage-relatedchangesintheskeletalsystemaffectthe joints as well as the quality and quantity of bone matrix. Thebonematrixinanolderboneismorebrittlethaninayoungerbonebecause decreased collagen production results in relatively moremineralandlesscollagenfibers.Withaging,theamountofmatrixalsodecreasesbecause therateofmatrix formationbyosteoblastsbecomesslowerthantherateofmatrixbreakdownbyosteoclasts. Bonemassisatitshighestaroundage30,andmengenerallyhavedenserbonesthanwomenbecauseoftheeffectsoftestosteroneand greater body weight. Race also affects bone mass. African-AmericansandHispanicshavehigherbonemassesthancaucasiansandAsians.Afterage35,bothmenandwomenexperiencealossofboneof0.3–0.5%ayear.Thislosscanincrease10-foldinwomenaftermenopause,whentheycanlosebonemassatarateof3–5%ayearforapproximately5–7years(seeSystemsPathology,“Osteoporosis”). Significantlossofboneincreasesthelikelihoodofbonefrac-tures.Forexample,lossoftrabeculaegreatlyincreasestheriskoffracturesofthevertebrae.Inaddition,lossofboneandtheresultingfractures can cause deformity, loss of height, pain, and stiffness.Lossofbonefromthejawscanalsoleadtotoothloss.

Movementofthefoottowardtheplantarsurface(soleofthefoot),aswhenstandingon the toes, iscommonlycalledplantar flexion.Movementofthefoottowardtheshin,aswhenwalkingontheheels,iscalleddorsiflexion.

acaSEinPoint

Dislocated Shoulder

theshoulderjointisthemostcommonlydislocatedjointinthebody.loosh Holder dislocated his shoulder joint while playing basketball.asaresultofa“charging”foul,looshwasknockedbackwardandfell.ashebrokehisfallwithhisextendedrightarm,theheadoftherighthumerus was forced out of the glenoid cavity.While being helpedup from the floor, loosh felt severe pain in his shoulder, his rightarm sagged, and he could not move his arm at the shoulder. Mostdislocations result in stretching of the joint capsule and movementofthehumeralheadtotheinferior,anteriorsideoftheglenoidcavity.thedislocatedhumeralheadismovedbacktoitsnormalpositionbycarefullypulling it laterallyover the inferior lipof theglenoidcavityand then superiorly into the glenoid cavity.once the shoulder jointcapsule has been stretched by a shoulder dislocation, the shoulderjoint may be predisposed to future dislocations. Some individualshave hereditary“loose” joints and are more likely to experience adislocatedshoulder.

Abduction (ab-dŭk′shun; to take away) is movement awayfromthemedianormidsagittalplane;adduction(tobringtogether)ismovementtowardthemedianplane(figure6.41c).Movingthelegsawayfromthemidlineofthebody,asintheoutwardmove-mentof“jumpingjacks,”isabduction,andbringingthelegsbacktogetherisadduction. Pronation (prō-nā′shŭn) and supination (soo′pi-nā′shun)arebestdemonstratedwiththeelbowflexedata90-degreeangle.Whentheelbowisflexed,pronationisrotationoftheforearmsothatthepalmisdown,andsupinationisrotationofthefore-armsothatthepalmfacesup(figure6.41d). Eversion(ē-ver′zhŭn)isturningthefootsothattheplantarsurface(bottomofthefoot)faceslaterally;inversion(in-ver′zhŭn)isturningthefootsothattheplantarsurfacefacesmedially. Rotationistheturningofastructurearounditslongaxis,asinshakingthehead“no.”Rotationofthearmcanbestbedemon-stratedwiththeelbowflexed(figure6.41e)sothatrotationisnotconfusedwithsupinationandpronationoftheforearm.Withtheelbowflexed,medialrotationofthearmbringstheforearmagainsttheanteriorsurfaceoftheabdomen,andlateralrotationmovesitawayfromthebody. Circumduction (ser-kŭm-dŭk′shŭn) occurs at freely mov-able joints, such as the shoulder. In circumduction, the armmovesso that itdescribesaconewith theshoulder jointat theapex(figure6.41f ). Inadditiontothemovementspicturedinfigure6.41,severalothermovementtypeshavebeenidentified:

• Protraction(prō-trak′shŭn)isamovementinwhichastructure,suchasthemandible,glidesanteriorly.

• Inretraction(rē-trak′shŭn),thestructureglidesposteriorly.• Elevationismovementofastructureinasuperiordirection.

Closingthemouthinvolveselevationofthemandible.


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SYSTEMS PATHOLOGY

OsteoporosisBackground InformationOsteoporosis, or porous bone, is a loss of bone matrix. This loss of bone mass makes bones so porous and weakened that they become deformed and prone to fracture (figure 6B). The occurrence of osteo-porosis increases with age. In both men and women (although it is 2.5 times more common in women), bone mass starts to decrease at about age 40 and continually decreases thereafter. Women can eventually lose approximately one-half, and men one-quarter, of their spongy bone.

In women, decreased production of the female reproductive hormone estrogen can cause osteoporosis, mostly in spongy bone, especially in the vertebrae of the spine and the bones of the fore-arm. Collapse of the vertebrae can cause a decrease in height or, in more severe cases, kyphosis in the upper back (figure 6D). Estrogen levels decrease after menopause, removal of the ovaries, amenor-rhea (lack of menstrual cycle) due to extreme exercise or anorexia nervosa (self-starvation) and cigarette smoking.

In men, reduction in testosterone levels can cause loss of bone tissue. However, this is less of a problem in men than in women because men have denser bones than women, and testosterone levels generally don’t decrease significantly until after age 65.

Inadequate dietary intake or absorption of calcium, sometimes due to certain medications, can also contribute to osteoporosis. Absorption of calcium from the small intes-tine decreases with age. Finally, too little exercise or disuse

from injury can all cause osteoporosis. Significant amounts of bone are lost after only 8 weeks of immobilization.

Skel

etal Osteoporosis

Background InformationOsteoporosisbone mass makes bones so porous and weakened that they become deformed and prone to fracture (figure 6B). The occurrence of osteo-porosis increases with age. In both men and women (although it is 2.5 times more common in women), bone mass starts to decrease at about age 40 and continually decreases thereafter. Women can eventually lose approximately one-half, and men one-quarter, of their spongy bone.

In women, decreased production of the female reproductive hormone estrogen can cause osteoporosis, mostly in spongy bone, especially in the vertebrae of the spine and the bones of the fore-arm. Collapse of the vertebrae can cause a decrease in height or, in more severe cases, kyphosis in the upper back (figure 6D). Estrogen levels decrease after menopause, removal of the ovaries, amenor-rhea (lack of menstrual cycle) due to extreme exercise or anorexia nervosa (self-starvation) and cigarette smoking.

bone tissue. However, this is less of a problem in men than in women because men have denser bones than women, and testosterone levels generally don’t decrease significantly until after age 65.

from injury can all cause osteoporosis. Significant amounts of bone are lost after only 8 weeks of immobilization.

Name: Betty Williams

Gender: Female

Age: 65

Comments

Betty has smoked

heavily for at least

50 years. She does not

exercise, seldom goes

outdoors, has a poor

diet, and is slightly underweight.

While attending a family picnic, Betty

tripped and fell. She reported severe right hip

pain and was not able to put any weight on

her right leg when she arrived in the ER.

Radiographs revealed signi� cant loss

of bone density and a fractured femur neck

(� gures 6B, 6C).

Name:

Gender:

Age:

Normalbone

Osteoporoticbone

FractureKyphosis

Figure 6BPhotomicrograph of osteoporotic bone and normal bone.

Figure 6CRadiograph

Figure 6D

see78267-Chapter06.indd 144 11-12-02 11:39 AM

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Skeletal

Early diagnosis of osteoporosis can lead to more preventativetreatments. instrumentsthatmeasuretheabsorptionofphotons(par-ticles of light) by bone are currently used; of these, dual-energy x-rayabsorptiometry (DExa) is considered the best. Supplementation ofdietary calcium and vitamin D and exercise are the best preventativeandrehabilitorymeasurestopreventbonelossorregainmildboneloss.calcitonin (Miacalcin) inhibits osteoclast activity, and alendronate(Fosamax),whichbinds tohydroxyapatite,also inhibitsosteoclasts.although osteoporosis is linked to estrogen loss, estrogen therapyhasbeenassociatedwithmanysideeffects,includingbreastcancer,andisnolongerrecommendedasatreatment.

OsteoporosisSymptoms

• Painandstiffnessespeciallyinspine

• Easilybrokenbones• lossofheight

Treatment• Dietarycalciumand

vitaminD• Exercise• calcitonin• alendronate

DIGESTIVEinadequatecalciumand

vitaminDintakecancauseinsufficientca2+absorptioninsmallintestine.

REPRODUCTIVEDecreasedestrogenfollowing

menopausecontributestoosteoporosis.

RESPIRATORYExcessivesmokinglowersestrogen

levels,whichincreasesboneloss.

ENDOCRINEcalcitoninisusedtotreatosteoporosis.

NERVOUSPainfrominjurymayreducefurtherinjury.

CARDIOVASCULARifbonebreakagehasoccurred,increasedbloodflowtothatsiteremovesdebris.Bloodcarriesnutrientsnecessaryforrepair.

LYMPHATIC AND IMMUNEimmunecellshelppreventinfectionaftersurgery,suchashipreplacement.

MUSCULARMuscleatrophyfromreducedactivity.increasedchanceoffallingandbreakingabone.

INTEGUMENTARYlimitedsunexposurelowersvitaminDproduction,which

reducesca2+absorption.

Predict 6

What advice should Betty give to her granddaughter so that the granddaughter will be less likely to develop osteoporosis when she is Betty’s age?


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degenerationofthejoints,withadvancingage.Inaddition,theligamentsandtendonssurroundingajointshortenandbecomeless flexible with age, resulting in decreased range of motion.Furthermore,manyolderpeoplearelessphysicallyactive,whichcauses the joints to become less flexible and decreases theirrangeofmotion. The most effective preventative measure against the effectsof aging on the skeletal system is the combination of increasingphysicalactivityandtakingdietarycalciumandvitaminDsupple-ments.Intensiveexercisecanevenreverselossofbonematrix.

DISEASES AND DISORDERS Skeletal System

CONDITION DESCRIPTIONtumors Maybemalignantorbenignandcausearangeofbonedefects

SkELETAL DISORDERS

Growth and Developmental Disorders

Gigantism abnormallyincreasedbodysizeduetoexcessivegrowthattheepiphysealplates

Dwarfism abnormallysmallbodysizeduetoimpropergrowthattheepiphysealplates

osteogenesisimperfecta Brittlebonesthatfractureeasilyduetoinsufficientorabnormalcollagen

rickets Growthretardationduetonutritionaldeficienciesinminerals(ca2+)orvitaminD;resultsinbonesthataresoft,weak,andeasilybroken

Bacterial Infections

osteomyelitis Boneinflammationoftenduetoabacterialinfectionthatmayleadtocompletedestructionofthebone

tuberculosis typically,alungbacteriumthatcanalsoaffectbone

Decalcification

osteomalacia Softeningofadultbonesduetocalciumdepletion;oftencausedbyvitaminDdeficiency

osteoporosis reductioninoverallquantityofbonetissue;seeSystemsPathology

JOINT DISORDERS

arthritis inflammationofajoint;causesincludeinfectiousagents,metabolicdisorders,trauma,andimmunedisorders

rheumatoidarthritis Generalconnectivetissueautoimmunedisease

Degenerativejointdisease (osteoarthritis)

Gradualdegenerationofajointwithadvancingage;canbedelayedwithexercise

Gout increasedproductionandaccumulationofuricacidcrystalsintissues,includingjointcapsules

Bursitis and bunions

Bursitis inflammationofabursa

Bunion Mostbunionsaredeformationsofthefirstmetatarsal(thegreattoe);bursitismayaccompanythisdeformity;irritatedbytightshoes

Jointreplacement replacementofpainfuljointswithartificialjoints

Gotowww.mhhe.com/seeleyess8foradditionalinformationonthesepathologies.

Anumberofchangesoccurwithinmanyjointsasapersonages.Changesinsynovialjointshavethegreatesteffectandoftenpresent major problems for elderly people. With use, the carti-lagecoveringarticularsurfacescanweardown.Whenapersonis young, production of new, resilient matrix compensates forthewear.Asapersonages,therateofreplacementdeclines,andthematrixbecomesmorerigid, thusadding to its rateofwear.The production rate of lubricating synovial fluid also declineswith age, further contributing to the wear of the articular car-tilage. Many people also experience arthritis, an inflammatory



section6.6,thelumbarvertebraesupportmoreweightthanotherregions of the vertebral column. thomas’ ruptured disk may berepairedwithprolongedbedrestoritmayrequiresurgery.onesuchtypeofsurgeryinvolvesremovingtheruptureddiskandreplacingit with a piece of hipbone. Eventually, the adjacent vertebrae willbecomefusedbyboneacrossthegap.

Answers to the rest of this chapter’s Predict questions are in Appendix E.

anSWErtolEarn To PrEDictSincethequestiontellsusthatthomassufferspainwhenbendingover, it is most likely that he has a ruptured intervertebral disk inhis lumbarregion.Whenthesedisksrupture,aportionofthediskprotrudesandpushesagainstthespinalcordorthespinalnerves,compromises their function,andproducespain.Herniationof theinferior lumbar disks is most common because, as you learned in

Theskeletalsystemconsistsofbone,cartilage,tendons,andligaments.

6.1 Functions of the Skeletal System (p. 110)

1. Theskeletalsystemprovidesthemajorsupportforthebody. 2. Boneprotectsinternalorgans. 3. Jointsallowmovementbetweenbones. 4. Bonesstoreandreleasemineralsasneededbythebody. 5. Bonemarrowgivesrisetobloodcellsandplatelets.

6.2 Extracellular Matrix (p. 111)

1. Bone,cartilage,tendons,andligamentsareconnectivetissues. 2. Varyingamountsofcollagen,proteoglycan,organicmolecules,

water,andmineralsinthematrixdeterminethecharacteristicsofconnectivetissue.

6.3 General Features of Bone (p. 111)

Therearefourcategoriesofbone:long,short,flat,andirregular.

Structure of a Long BoneLongbonesconsistofadiaphysis(shaft),epiphyses(ends),andepiphyseal(growth)plates.Thediaphysiscontainsamedullarycavity,whichisfilledwithmarrow,andtheendoftheepiphysisiscoveredbyarticularcartilage.

Histology of Bone 1. Osteoblastsarebone-formingcells. 2. Osteocytesarebonecellslocatedbetweenthinsheetsofextracellular

matrixcalledlamellae. 3. Compactbonetissueconsistsofosteons,whicharecomposedof

osteocytesorganizedintolamellaesurroundingcentralcanals. 4. Spongybonetissueconsistsoftrabeculaewithoutcentralcanals.

Bone Ossification 1. Intramembranousossificationoccurswithinconnectivetissue

membranes. 2. Endochondralossificationoccurswithincartilage.

Bone GrowthBoneelongationoccursattheepiphysealplateaschondrocytesproliferate,enlarge,die,andarereplacedbybone.

Bone RemodelingBoneremodelingconsistsofremovalofexistingbonebyosteoclastsanddepositionofnewbonebyosteoblasts.

Bone RepairDuringbonerepair,cellsmoveintothedamagedareaandformacallus,whichisreplacedbybone.

6.4 Bone and Calcium Homeostasis (p. 117)

1. Osteoclastsremovecalciumfrombone,causingbloodcalciumlevelstoincrease.

2. Osteoblastsdepositcalciumintobone,causingbloodcalciumlevelstodecrease.

3. Parathyroidhormoneincreasesbonebreakdown,whereascalcitonindecreasesbonebreakdown.

6.5 General Considerations of Bone Anatomy (p. 119)

Thereare206bonesintheaverageadultskeleton.

6.6 Axial Skeleton (p. 120)

Theaxialskeletonincludestheskull,vertebralcolumn,andthoraciccage.

Skull 1. Theskullconsistsof22bones:8formingthebraincaseand14facial

bones.Thehyoidboneand6auditoryossiclesareassociatedwiththeskull.

2. Fromalateralview,theparietal,temporal,andsphenoidbonescanbeseen.

3. Fromafrontalview,theorbitsandnasalcavitycanbeseen,aswellasassociatedbonesandstructures,suchasthefrontalbone,zygomaticbone,maxilla,andmandible.

4. Theinteriorofthecranialcavitycontainsthreefossaewithseveralforamina.

5. Seenfrombelow,thebaseoftheskullrevealsnumerousforaminaandotherstructures,suchasprocessesformuscleattachment.

Vertebral Column 1. Thevertebralcolumncontains7cervical,12thoracic,and5lumbar

vertebrae,plus1sacralboneand1coccyxbone. 2. Eachvertebraconsistsofabody,anarch,andprocesses. 3. Regional differences in vertebrae are as follows: Cervical vertebrae

have transverse foramina; thoracic vertebrae have long spinousprocesses and attachment sites for the ribs; lumbar vertebrae haverectangular transverse and spinous processes, and the position oftheir facets limits rotation; the sacrum is a single, fused bone; thecoccyxis4orfewerfusedvertebrae.

SuMMarY


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6.8 Joints (p. 138)

Ajointisaplacewherebonescometogether.

Fibrous JointsFibrousjointsconsistofbonesunitedbyfibrousconnectivetissue.Theyallowlittleornomovement.

Cartilaginous JointsCartilaginousjointsconsistofbonesunitedbycartilage,andtheyexhibitslightmovement.

Synovial Joints 1. Synovialjointsconsistofarticularcartilageovertheunitingbones,

ajointcavitylinedbyasynovialmembraneandcontainingsynovialfluid,andajointcapsule.Theyarehighlymovablejoints.

2. Synovialjointscanbeclassifiedasplane,saddle,hinge,pivot,ball-and-socket,orellipsoid.

Types of MovementThemajortypesofmovementareflexion/extension,abduction/adduction,pronation/supination,eversion/inversion,rotation,circumduction,protraction/retraction,elevation/depression,excursion,andopposition/reposition.

6.9 Effects of Aging on the Skeletal System and Joints (p. 143)

1. Bonematrixbecomesmorebrittleanddecreasesintotalamountduringaging.

2. Jointslosearticularcartilageandbecomelessflexiblewithage. 3. PreventionmeasuresincludeexerciseandcalciumandvitaminD

supplements.

Rib Cage 1. Theribcageconsistsofthethoracicvertebrae,theribs,andthe

sternum. 2. Thereare12pairsofribs:7trueand5false(2ofthefalseribsare

alsocalledfloatingribs). 3. Thesternumconsistsofthemanubrium,thebody,andthexiphoid

process.

6.7 Appendicular Skeleton (p. 129)

Theappendicularskeletonconsistsofthebonesoftheupperandlowerlimbsandtheirgirdles.

Pectoral GirdleThepectoralgirdleincludesthescapulaeandclavicles.

Upper LimbTheupperlimbconsistsofthearm(humerus),forearm(ulnaandradius),wrist(8carpalbones),andhand(5metacarpalbones,3phalangesineachfinger,and2phalangesinthethumb).

Pelvic GirdleThepelvicgirdleismadeupofthe2coxalbones.Eachcoxalboneconsistsofanilium,anischium,andapubis.Thecoxalbones,sacrum,andcoccyxformthepelvis.

Lower LimbThelowerlimbincludesthethigh(femur),leg(tibiaandfibula),ankle(7tarsalbones),andfoot(metatarsalbonesandphalanges,similartothebonesinthehand).

1. Whataretheprimaryfunctionsoftheskeletalsystem? 2. Namethemajortypesoffibersandmoleculesintheextracellular

matrixoftheskeletalsystem.Howdotheycontributetothefunctionsoftendons,ligaments,cartilage,andbones?

3. Definediaphysis,epiphysis,epiphysealplate,medullarycavity,articularcartilage,periosteum,andendosteum.

4. Describethestructureofcompactbone.Howdonutrientsreachtheosteocytesincompactbone?

5. Describethestructureofspongybone.Whataretrabeculae?Howdonutrientsreachosteocytesintrabeculae?

6. Defineanddescribeintramembranousandendochondralossification.

7. Howdobonesgrowindiameter?Howdolongbonesgrowinlength? 8. Whatisaccomplishedbyboneremodeling?Howdoesbonerepair

occur? 9. Definetheaxialskeletonandtheappendicularskeleton.10. Namethebonesofthebraincaseandtheface.11. Givethelocationsoftheparanasalsinuses.Whataretheir

functions?12. Whatisthefunctionofthehardpalate?13. Throughwhatforamendoesthebrainconnecttothespinalcord?

14. Howdothevertebraeprotectthespinalcord?Wheredospinalnervesexitthevertebralcolumn?

15. Nameandgivethenumberofeachtypeofvertebra.Describethecharacteristicsthatdistinguishthedifferenttypesofvertebraefromoneanother.

16. Whatisthefunctionofthethoraciccage?Namethepartsofthesternum.Distinguishamongtrue,false,andfloatingribs.

17. Namethebonesthatmakeupthepectoralgirdle,arm,forearm,wrist,andhand.Howmanyphalangesareineachfingerandinthethumb?

18. Definethepelvicgirdle.Whatbonesfusetoformeachcoxalbone?Whereandwithwhatbonesdothecoxalbonesarticulate?

19. Namethebonesofthethigh,leg,ankle,andfoot.20. Definejoint,orarticulation.Nameanddescribethedifferences

amongthethreemajorclassesofjoints.21. Describethestructureofasynovialjoint.Howdothedifferentparts

ofthejointpermitjointmovement?22. Onwhatbasisaresynovialjointsclassified?Describethedifferent

typesofsynovialjoints,andgiveexamplesofeach.Whatmovementsdoeseachtypeofjointallow?

23. Describeandgiveexamplesofflexion/extension,abduction/adduction,andsupination/pronation.

rEViEWanDcoMPrEHEnSion



1. A12-year-oldboyfellwhileplayingbasketball.Thephysicianexplainedthatthehead(epiphysis)ofthefemurwasseparatedfromtheshaft(diaphysis).Althoughthebonewassetproperly,bythetimetheboywas16,itwasapparentthattheinjuredlowerlimbwasshorterthanthenormalone.Explainwhythisdifferenceoccurred.

2. JustinTimeleapedfromhishotelroomtoavoidburningtodeathinafire.Ifhelandedonhisheels,whatbonewaslikelytofracture?UnfortunatelyforJustin,a240-poundfireman,HeftyStomper,ranbyandsteppedheavilyonthedistalpartofJustin’sfoot(notthetoes).Whatbonesnowcouldbebroken?

3. Onedaywhileshopping,Ms.WanttaBargainpickedupher3-year-oldson,Somm,byhisrightwristandliftedhimintoashoppingcart.Sheheardaclickingsound,andSommimmediatelybegantocryandholdhiselbow.Giventhatliftingthechildcausedaseparationattheelbow,whichismorelikely:separationoftheradiusandhumerus,orseparationoftheulnaandhumerus?

4. Whyarewomenknock-kneedmorecommonlythanmen? 5. Askeletonwasdiscoveredinaremotemountainarea.Thecoroner

determinedthatnotonlywastheskeletonhuman,butitwasfemale.Explain.

Answers in Appendix D

criticaltHinKinG

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6Bones and Joints - Mrs. Pillar's A & P Website

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