2The science of bones is called osteology Functions of boneSupport & protect organsThe brain is protected by the skull and the heart and lungs are protected the ribs & sternumMovementMuscles attach to skeletonInorganic salt storageStores calcium and phosphateBlood cell productionRed bone marrow forms new blood cells
3Components of boneThe extracellular matrix of bones is composed of1. hydroxyapatite – a calcium phosphate salt that providesthe hardness of bones2. collagen fibers – provides bone with some pliabilityThe cells associated with bones include:Osteocytes = cells that maintain boneOsteoblasts = cells that deposit new bone. Once mature, osteoblasts become osteocytes.Osteoclasts = cells that dissolve bone. Osteoclasts originate from white blood cells and they secrete an acid that dissolves the inorganic salts of bone.
4Bones may be classified by their shape. Long bones = elongated diaphysishumerus radius ulnafemur tibia fibulametatarsals metacarpals phalangesShort Bones = cube-shapedcarpalstarsalsFlat Bones = plate-likesternum ribs scapulaparietal and frontal bones
5Bone Classification continued Irregular bones = variety of shapesvertebraemandible maxillaethmoid bone sphenoid bonesesamoid (or round) bone = develops within tendonspatella
6Parts of a long bone Diaphysis = shaft of long bone Lined with compact boneEpiphysis = expanded ends of boneFilled with spongy boneProximal epiphysis & distal epiphysisSites of articulation (joint)Epiphyseal platesRemnants of bone growthArticular cartilageHyaline cartilageCovers epiphyses
7Parts of a long bone Medullary Cavity Cavity within diaphysis Filled with bone marrow, blood vessels and nervesEndosteumMembrane that lines medullary cavityContains osteoblastsPeriosteumTough membrane covering boneContinuous with tendons and ligamentsOsteoblasts, blood vessels, and nerves
8Parts of a long bone Compact bone Lines the Diaphysis Composed of osteonsSpongy boneFills the epiphysesTrabiculae = thin bony platesOsteocytes lie within trabiculaeFigure 7.3
9Compact Bone Osteon = Structural & functional unit of compact bone Lamella = concentric rings of boneCentral Canal = blood vessels and nervesLacunae = bony chamber that contains an osteocyteCanaliculi = canals with cellular processesPathway for nutrient and waste diffusionFigure 7.5 Scanning electron micrograph of a single osteon in compact bone.
10Osteon continuedPerforating Canal = conveys blood from periosteum towards individual osteons
11Figure 7.4 Compact bone is composed of osteons cemented together by bone matrix. Figure 7.4c Canaliculi allow nutrients and waste to diffuse between the central canal and individual osteocytes.
12Bone Development and Growth Parts of the skeletal system begin to develop during the firstfew weeks of prenatal developmentBone formation = ossificationBones replace existing connective tissue in one of two ways:As intramembranous bonesAs endchondral bones
13Intramembranous Bones Broad, flat bones of the skullFormed by replacing layers ofconnective tissue (mesenchyme)with boneOsteoblasts within mesenchymedeposit bony matrix in all directionsOsteoblasts become osteocytesonce surrounded by bone
14Endochondral Bones Endochondral Bones Most of the bones in the skeleton are endochondralBone formation begins with a hyaline cartilage modelCartilage decomposes and is replaced by bone.Figure 7.6a stained bones of a 14-week fetus showing intramembranous and endochorndal bones.
15Endochondral Ossification Hyaline cartilage forms model of future boneCartilage degenerates and periosteum surrounds boneOsteoblasts from periosteum invade the degenerating tissueOsteoblasts beneath periosteum form compact bone at diaphysis = primary ossification centerLater, Osteoblasts form spongy bone at epiphyses = secondary ossification center
16Endochondral Ossification continued Figure 7.8 Major stages of endochondral ossification. (a-d fetal, e child, f adult)
17Endochondral Ossification Two areas of endochondral bone retain cartilage after ossification.Articular cartilagesurrounds the epiphyses for jointsEpiphyseal platesretain cartilage for bone growthArticular cartilage
18Growth at the Epiphyseal Plate Band of hyaline cartilage that remainsbetween the two ossification centersBone growth continues at epiphysealplates until adulthood.New cartilage is added towards the epiphysisand cartilage is ossified towards diaphysisOnce the epiphyseal plates ossify thebones can no longer be lengthened
194 Layers (zones) of growth at epiphyseal Plate Zone of resting cartilageCartilage cells near epiphysisDo not participate in bone growthAnchor epiphyseal plate to epiphysisZone of proliferating cartilageYoung chondrocytes undergoing mitosisAdds new cartilage to plate
204 Layers (zones) of growth at epiphyseal Plate Zone of hypertrophic cartilageOlder cells enlarge and thicken the epiphyseal plateOsteoblasts invade and calcify the cartilaginous matrix.Zone of calcified cartilageDead cells & calcium matrixOssified boneOsteoclasts dissolve and phagocytizethe matrixOsteoblasts invade the region anddeposit new bone.(b)End of Section 1, Chapter 7Figure 7.9a
22Homeostasis of Bone Tissue Calcium is constantly exchanged between the blood and bone.Bone resorption = Osteoclasts breakdown bone releasing calcium into the blood. Bone resorption occurs when blood [Ca2+] is low and it’s stimulated by parathyroid hormone (PTH).Bone deposition = Osteoblasts deposit new bone from calcium in the blood stream. Bone deposition occurs when blood [Ca2+] is high and it’s stimulated by the hormone calcitonin.
23Nutrients that effect bone homeostasis Vitamin D – promotes Ca2+ absorption in small intestineVitamin D deficiency = softened and deformed bonesOsteomalacia in adultsRickets in childrenVitamin A – balances bone resorption and depositionVitamin A deficiency = retards bone developmentVitamin C – is required for collagen synthesis.Vitamin C deficiency = results in fragile bones
24Hormones that affect bone homeostasis CalcitoninSecreted from thyroid glandPromotes bone depositionParathyroid Hormone (PTH)Secreted from parathyroid glandsPromotes bone resorptionFigure 7.13 Hormonal regulation of blood calcium and resorption
25Hormones that affect bone homeostasis Growth Hormone (GH)Secreted from pituitary glandPromotes bone growth at epiphyseal platesPituitary Gigantismover secretion of GH during childhoodPituitary Dwarfisminsufficient GH during childhoodAcromegalyOver secretion of GH as an adultOccurs after epiphyseal plates have sealedEnlargement of hands, feet, nose
26Hormones that affect bone homeostasis Sex Hormones (testosterone & estrogen)Promotes long bone growth at pubertySex hormones also stimulate ossification at epiphyseal plates.Effects of Exercise on bone homeostasisContracting muscles pull on bones and promotes bone thickeningFigure 7.12 The thickened bone on the left is better able to withstand forces from muscle contractions.
29Repair of a fracture Step 1. hematoma formation When a bone breaks blood vessels rupture and the periosteum tears.The repair of a broken bone occurs in 5 general steps.Step 1. hematoma formationBlood soon forms a hematoma (blood clot).Hematoma in foot
30Repair of a fracture Step 2. temporary spongy bone Osteoblasts invade from periosteum and deposit temporary spongy bone.Step 3. cartilaginous callusFibroblasts deposit a mass of fibrocartilage “cartilaginous callus”&Phagocytes remove hematomaOsteoclasts remove bony debris
31Repair of a fracture Step 4. bony callus Step 5. bone remodeling Osteoblasts replace the cartilaginous callus with bone, forming a bony callusStep 5. bone remodelingOsteoclasts remove excess bone, remodeling the bone the bone close to its original shape.
32Disorders of BoneOver time, osteoclasts outnumber osteoblasts, and more bone is resorbed than can be deposited. Bone mass decreases as a result.Bone loss is rapid in menopausal women due to reduced estrogenOsteopenia “low bone mass”Progresses towards osteoporosisOsteoporosis “porous bone”Bones develop spaces and canalsBones are fragile and easily brokenCommon in menopausal women(from the low estrogen levels)
33End of Chapter 7, Section 2 Ways to delay or prevent osteoporosis: Exercise daily.Consume enough calcium and vitamin D every day.Do not smoke.End of Chapter 7, Section 2