Lecture 15 Bone

Last time - respiratory tract

Respiratory tract -upper tract -larynx -trachae -primary (main) bronchi -lower tract (lungs) -bronchi -bronchioles -respiratory bronchioles -alveolar ducts -alveoli

Skeletal system-Introduction

Skeletal System -bone, cartilage, and tendon + ligaments -bone and bone formation -bone functions -support and attachment of muscle -protection of soft organs -storage and mobilization of calcium -marrow (blood cells)

Skeletal system-bone structure

Bone -organ (structure) -compact bone -cancellous (spongy) bone -long bones = model -shaft = diaphysis -ends = epiphysis -articular cartilage -metaphysis -shaft meets ends -covering = periosteum -lining = endosteum

Skeletal system-bone structure

Bone -cells -osteoprogenitor -osteoblasts -osteocytes -osteoclasts -coverings -periosteum -endosteum -matrix -osteoid

Skeletal system-bone cells

Bone Cells

Skeletal system-bone cells

Osteoblasts -located outside bone -periosteum (under CT) -endosteum -synthesize bone -secrete osteoid (matrix) -inactive = squamous -active = cuboidal -ultrastructure -RER (making protein) -golgi (packaging) -vesicles (export)

Skeletal system-bone cells

Osteocytes -located inside bone -surrounded by matrix -lacunae -canaliculi -gap junctions

Skeletal system-bone cells

Osteoclasts -located surface bone -large multinucleate -derived eosinophil/monocyte lineage -bone re-absorption -enzymes, acid -endocytosis, vesicles -blood vessels -ruffled zone = absorption -clear zone = adhesion

Skeletal system-bone cells

Osteoclasts -regulate calcium levels -balance diet/stores -hormonal regulation -PTH (parathyroid) -osteoclasts active -kidney & digestive system absorb Ca -Calcitonin (thyroid) -osteoclasts off -osteoblasts on -kidneys remove Ca -digestive ignores Ca

Skeletal system-bone coverings

Periosteum -exterior surface bone -outer fibrous layer -dense irregular connective tissue -blood vessels -nerves -inner cellular layer -osteogenic layer -looser connective tissue -cuboidal cells (active) -continuity with collagen of bone -sharpey’s fibres

Skeletal system-bone coverings

Endosteum -interior surface bone -lines marrow cavity -simple squamous -simple cuboidal (active)

Skeletal system-bone formation

Bone formation -70% inorganic salts -hydroxyapatite -calcium -phosphorus -30% organic molecules -90% collagen -10% ground substance -prior to mineralization -osteoid -new (woven) bone -low mineralization

Skeletal system-bone structure

Primary Bone -woven bone (immature bone) -collagen arrays are random -low mineral content -lots of osteocytes

Secondary Bone -collagen arrays oriented -lamellae -collagen parallel in lamellae -highly mineralized -fewer osteocytes

Skeletal system-bone structure

Secondary Bone - lameller bone -remodeled bone -compact bone -solid, dense -cancellous bone -trabecular spongy bone

cancellous

compact

Skeletal system-compact bone

Compact Bone -exterior (peripheral) -circumferential lamellae -periosteum -interior (medial) -circumferential lamellae -endosteum -lamellae organization -osteon (haversian system) -parallel collagen fibers -each lamella perpendicular -remodeled lamella -interstitial

Skeletal system-compact bone

Compact Bone -osteon -central blood vessels/nerves -osteocytes in lacunae -connections = canaliculi -interstitial lamellae

Skeletal system-compact bone

Cancellous/Spongy Bone -branched -trabeculae -2-4 cell layers thick -lamellae etc but no haversian system

cancellous

compact

Skeletal system-bone development

Bone development -intramembranous ossification -osteoblasts in CT -direct mineralization of matrix -endochondral ossification -mineralization of cartilage model -both processes make primary bone -both can result in -spongy/cancellous bone -compact bone

Skeletal system-bone development

Intramembranous ossification -formation of flat bones -skull -produces both compact and spongy bone -baby (soft spot)

Skeletal system-bone development

Intramembranous ossification -condensation of mesenchymal connective tissue -fibroblast > osteoblast -direct formation of bone islands -trabeculae -appositional growth (thicker)

Skeletal system-bone development

Endochondral ossification -allows function during development -cartilage model -large lacunae -progressive calcification -cartilage regresses -perichondrium >> periosteum -osteoblasts -woven bone -invasion by mesenchyme -blood vessels -primary ossification site -cartilage model grows at ends -epiphysial plate -bone grows longer -secondary site of ossification Text pg 184

Skeletal system-bone development

Epiphysial plate -distal ends of bone = cartilage -site of growth -4 zones -resting zone (reserve cartilage) -hyaline cartilage -zone of proliferation -chondrocyte mitosis -columns of lacunae -zone of hypertrophy -lacunae enlarge -cartilage calcified (basophilic) -zone of ossification (osteogenic) -invasion by capillaries -osteoblasts -bone over cartilage (acidophilic)

Skeletal system-bone development

Epiphysial plate 1-resting zone (reserve cartilage) 2-zone of proliferation 3-zone of hypertrophy 4-zone of ossification (osteogenic)

proliferation

hypertrophy

ossification

Skeletal system-bone remodeling

Appositional growth -growth from exterior -form new osteons -repeat -look inside long bones

Skeletal system-bone remodeling

Bone remodeling -bone dynamic tissue -constant remodeling -length via epiphysial plate -girth by appositional growth -fracture repair recapitulates formation