The Skeletal System. Parts of the skeletal system Bones (skeleton) Joints Cartilages Ligaments Two subdivisions of the skeleton Axial skeleton Appendicular.

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The Skeletal SystemThe Skeletal SystemParts of the skeletal systemBones (skeleton)JointsCartilagesLigamentsTwo subdivisions of the skeletonAxial skeletonAppendicular skeletonFunctions of BonesSupport the bodyProtect soft organsAllow movement due to attached skeletal musclesStore minerals and fatsBlood cell formationBones of the Human BodyThe adult skeleton has 206 bonesTwo basic types of bone tissueCompact boneHomogeneousSpongy boneSmall needle-like pieces of boneMany open spacesFigure 5.2bClassification of Bones on the Basis of ShapeFigure 5.1Classification of BonesLong bonesTypically longer than they are wideHave a shaft with heads at both endsContain mostly compact boneExample:FemurHumerusClassification of BonesFigure 5.1aClassification of BonesShort bonesGenerally cube-shapeContain mostly spongy boneExample:CarpalsTarsalsClassification of BonesFigure 5.1bClassification of BonesFlat bonesThin, flattened, and usually curvedTwo thin layers of compact bone surround a layer of spongy boneExample: SkullRibsSternumClassification of BonesFigure 5.1cClassification of BonesIrregular bonesIrregular shapeDo not fit into other bone classification categoriesExample: Vertebrae Hip bonesClassification of BonesFigure 5.1dAnatomy of a Long BoneDiaphysisShaftComposed of compact boneEpiphysis Ends of the boneComposed mostly of spongy boneAnatomy of a Long BonePeriosteumOutside covering of the diaphysisFibrous connective tissue membraneSharpeys fibersSecure periosteum to underlying boneArteriesSupply bone cells with nutrientsAnatomy of a Long BoneFigure 5.2cAnatomy of a Long BoneArticular cartilageCovers the external surface of the epiphysesMade of hyaline cartilageDecreases friction at joint surfacesAnatomy of a Long BoneEpiphyseal plateFlat plate of hyaline cartilage seen in young, growing boneEpiphyseal lineRemnant of the epiphyseal plateSeen in adult bonesAnatomy of a Long BoneFigure 5.2aAnatomy of a Long BoneMedullary cavity Cavity inside of the shaftContains yellow marrow (mostly fat) in adultsContains red marrow (for blood cell formation) in infantsAnatomy of a Long BoneFigure 5.2aBone MarkingsSurface features of bonesSites of attachments for muscles, tendons, and ligamentsPassages for nerves and blood vesselsCategories of bone markingsProjections or processesgrow out from the bone surfaceDepressions or cavitiesindentationsBone MarkingsTable 5.1 (1 of 2)Bone MarkingsTable 5.1 (2 of 2)Microscopic Anatomy of BoneOsteon (Haversian system)A unit of bone containing central canal and matrix ringsCentral (Haversian) canalOpening in the center of an osteonCarries blood vessels and nervesPerforating (Volkmans) canalCanal perpendicular to the central canalCarries blood vessels and nervesMicroscopic Anatomy of BoneFigure 5.3aMicroscopic Anatomy of BoneLacunaeCavities containing bone cells (osteocytes)Arranged in concentric ringsLamellaeRings around the central canalSites of lacunaeMicroscopic Anatomy of BoneFigure 5.3bcMicroscopic Anatomy of BoneCanaliculi Tiny canalsRadiate from the central canal to lacunaeForm a transport system connecting all bone cells to a nutrient supplyFormation of the Human SkeletonIn embryos, the skeleton is primarily hyaline cartilageDuring development, much of this cartilage is replaced by boneCartilage remains in isolated areasBridge of the noseParts of ribsJointsBone Growth (Ossification)Epiphyseal plates allow for lengthwise growth of long bones during childhoodNew cartilage is continuously formedOlder cartilage becomes ossifiedCartilage is broken downEnclosed cartilage is digested away, opening up a medullary cavityBone replaces cartilage through the action of osteoblastsBone Growth (Ossification)Bones are remodeled and lengthened until growth stopsBones are remodeled in response to two factorsBlood calcium levelsPull of gravity and muscles on the skeletonBones grow in width (called appositional growth)Long Bone Formation and GrowthFigure 5.4aLong Bone Formation and GrowthFigure 5.4bTypes of Bone CellsOsteocytesmature bone cellsOsteoblastsbone-forming cellsOsteoclastsbone-destroying cellsBreak down bone matrix for remodeling and release of calcium in response to parathyroid hormoneBone remodeling is performed by both osteoblasts and osteoclasts

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