The Skeletal System. Skeletal System Notes Standard SAP2b. Explain how the skeletal structures provide support and protection for tissues EQ: How do bones

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The Skeletal SystemSkeletal System NotesStandard SAP2b. Explain how the skeletal structures provide support and protection for tissuesEQ: How do bones and the skeletal system function to help the body maintain homeostasis?

The Skeletal SystemParts of the skeletal systemBones (skeleton)JointsCartilagesLigamentsDivided into two divisionsAxial skeletonAppendicular skeletonFunctions of BonesSupport of the bodyProtection of soft organsMovement due to attached skeletal musclesStorage of minerals and fatsBlood cell formation

Bones of the Human BodyThe adult skeleton has 206 bonesTwo basic types of bone tissueCompact boneHomogeneousSpongy boneSmall needle-like pieces of boneMany open spacesFigure 5.2b

Classification of Bones on the Basis of ShapeFigure 5.1

Classification of BonesLong bonesTypically longer than wideHave a shaft with heads at both endsContain mostly compact boneExamples: Femur, humerus

Classification of BonesShort bonesGenerally cube-shapeContain mostly spongy boneExamples: Carpals, tarsals

Classification of BonesFlat bonesThin and flattenedUsually curvedThin layers of compact bone around a layer of spongy boneExamples: Skull, ribs, sternum

Classification of BonesIrregular bonesIrregular shapeDo not fit into other bone classification categoriesExample: Vertebrae and hip

Classification of Bones on the Basis of ShapeFigure 5.1

Gross Anatomy of a Long BoneDiaphysisShaftComposed of compact boneEpiphysis Ends of the boneComposed mostly of spongy boneFigure 5.2a

Structures of a Long BonePeriosteumOutside covering of the diaphysisFibrous connective tissue membraneSharpeys fibersSecure periosteum to underlying boneArteriesSupply bone cells with nutrientsFigure 5.2c

Structures of a Long BoneArticular cartilageCovers the external surface of the epiphysesMade of hyaline cartilageDecreases friction at joint surfacesFigure 5.2a

Structures of a Long BoneMedullary cavityCavity of the shaftContains yellow marrow (mostly fat) in adultsContains red marrow (for blood cell formation) in infantsFigure 5.2a

Bone MarkingsSites of attachments for muscles, tendons, and ligamentsCategories of bone markingsProjections and processes grow out from the bone surfaceDepressions or cavities indentations

Summary3-2-13 facts that you learned2 things that you found interesting1 question that you haveMicroscopic Anatomy of BoneStandard SAP2b. Explain how the skeletal structures provide support and protection for tissues

EQ: How does the microscopic structure of bones contribute to the functions of bones?

Microscopic Anatomy of Compact BoneOsteon (Haversian System)A unit of boneCentral (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 Compact BoneFigure 5.3

Microscopic Anatomy of Compact BoneLacunaeCavities containing bone cells (osteocytes)Arranged in concentric ringsLamellaeRings around the central canalSites of lacunaeDetail of Figure 5.3

Microscopic Anatomy of Compact BoneCanaliculi Tiny canalsRadiate from the central canal to lacunaeForm a transport systemSupply O2 and nutrients to osteocytes.

Microscopic Anatomy of Spongy BoneDoes not contain osteonsConsists of units called trabeculaeIrregular latticework of thin columns of bone tissueSpaces between trabeculae filled with red marrowIn hip bones, ribs, sternum, backbone, ends of long bones.

Trabeculae structure

SummarizerDescribe the difference between compact bone and spongy bone in terms of gross and microscopic anatomy.Types of Bone CellsOsteogenic CellsUnspecialized stem cellsOnly bone cells that undergo cell divisionOsteocytesMature bone cellsOsteoblastsBone-forming cellsOsteoclastsBone-destroying cellsBreak down bone matrix for remodeling and release of calcium

Bone FormationOssification the process by which bones formBone growth occurs in 4 situations:Initial formation in an embryo/ fetusGrowth during infancy, childhood, and adolescence until adulthoodRemodeling replacing old tissue with newRepair after a fractureInitial Bone FormationSkeleton begins as mesenchyme embryonic connnective tissue that forms all other tissues2 methods of bone formationIntramembranous ossification Bone forms in mesenchyme in sheet like layersEndochondral ossification Bone forms in hyaline cartilage made from mesenchymeIntramembranous ossificationSimpler methodForms flat bones of skull and mandibleSteps:1. Ossification center develops site where bone will be madeOsteoblasts secrete extracellular matrix of bone2. Calcification calcium and other mineral salts are deposited to harden the extracellular matrix3. Trabeculae form as the extracellular matrix hardens to form spongy bone4. Periosteum develops from mesenchyme around the outside of bone - a layer of compact bone replaces surface layers of spongy boneEndochondral Ossification

Bone Growth in LengthOccurs at epiphyseal plateNew cartilage cells (chondrocytes) added to epiphyseal side of the plateOld chondrocytes on diaphyseal side turn into bone tissueDiaphyseal side increases in lengthBone Growth in ThicknessOsteoblasts add bone tissue to the outside Osteoclasts break down bone on the insideMedullary cavity enlarges as bone thickness increasesBone RemodelingOngoing process of replacing old bone tissue with newBone resporption removal of minerals and collagen fibers by osteoclastsBone deposition - addition of minerals and collagen fibers to bone by osteoblasts

Bone Fractures

Bone Fracture Repair1. phagocytes remove dead bone tissue2. chonroblasts (cartilage forming cells) form cartilage at the fracture site 3. fibrocartilage converted to spongy bone4. bone remodeling occurs -> osteoclasts absorb dead bone, spongy bone converted to compact boneTakes longer to heal because calcium is deposited gradually

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