spicule Osseous tissue Resting zone Proliferation zone Cartilage cells undergo

Spicule osseous tissue resting zone proliferation

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spiculeOsseous tissue Resting zoneProliferation zoneCartilage cells undergo mitosis.Hypertrophic zoneOlder cartilage cells enlarge.Ossification zoneNew bone formation is occurring.Calcification zoneMatrix becomes calcified; cartilage cells die; matrix begins deteriorating.123469Epiphyseal plateResting zone: cells nearest the epiphysis that are relatively small and inactiveColumns of stacked cartilage cells are inside the resting zone (in direction of diaphysis)Proliferation zone is made up of chondroblasts at the top of the stack which divide quickly which pushes the epiphysis away from the diaphysis causing the bone to elongateHypertrophic zone: older chondrocytes have enlarged (hypertrophied) and are positioned deep in the stack Calcification zone: The older hypertrophied chondrocytes signal the surrounding cartilage matrix to calcify and produce a calcification zoneOssification zone: new bone formation 70Postnatal Childhood and Adolescent Growth of Endochondrial BonesBones lengthen entirely by growth from the epiphyseal platesCartilage is replaced with bone tissue in diaphysis side as quickly as it growsWhole bone lengthensEpiphyseal plate maintains constant thickness during growth of diaphysis71Postnatal Growth of Endochondrial BonesGrowing bones widen as they lengthenOsteoblasts—add bone tissue to the external surface along the diaphysisOsteoclasts—remove bone from the internal surface along the diaphysis as remodeling takes place with increase in diameterAppositional growth—growth of a bone by addition of bone tissue to its surface72
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5/12/1713Hormone Regulation of Bone GrowthGrowth hormone—produced by the pituitary gland– Stimulates epiphyseal platesThyroid hormone—ensures that the skeleton retains proper proportionsSteroid hormones(estrogen and testosterone)– Promote bone growth– Later induce closure of epiphyseal plates73At end of adolescence, long bone growth endsChondroblasts divide less often and then stop dividingEpiphyseal plates become thinnerCartilage stops growing and is replaced by bone tissueLong bones stop lengthening when the bone of the diaphysis and epiphysis fuse and epiphyseal plates closePeople can no longer grow in height once their epiphyseal plates have closed74Bone Remodeling: bone is a dynamic tissue500 mg of calcium may enter or leave the adult skeleton each dayCancellous (spongy) bone of the skeleton is replaced every 3–4 years in most bonesCompact bone is replaced every 10 years in most bones75Bone deposition and resorptionOccurs at periosteal (periosteum) and endosteal(endosteum) surfacesIn adults, this occurs primarily at the endosteal surface 76Bone RemodelingBone deposition/formationaccomplished by osteoblastsBone resorption—accomplished by osteoclastsMaintains normal levels of Ca+ and PO43-in body fluids
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