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1Dariusz Borys MD firstname.lastname@example.org www.pedorthpath.com BONE PATHOLOGYDariusz Borys MD
2OBJECTIVES Identify main functions of bone tissue Identify the major parts of a long bonesDescribe the cells found in bone tissueDescribe the components of an osteonCompare and contrast intramembranous and endochondral ossification.
3BONE FUNCTION Support Protection (protect internal organs) Movement (provide leverage system for skeletal muscles, tendons, ligaments and joints)Mineral homeostasis (bones act as reserves of minerals important for the body like calcium or phosphorus)Hematopoiesis: blood cell formationStorage of adipose tissue: yellow marrow
4SHAPE OF BONES Long bones (e.g., humerus, femur) Short bones (e.g., carpals, tarsals, patella)Flat bones (e.g., parietal bone, scapula, sternum)Irregular bones (e.g., vertebrae, hip bones)
5BONE ANATOMYDiaphysis: long shaft of boneEpiphysis: ends of boneEpiphyseal plate: growth plateMetaphysis: b/w epiphysis and diaphysisArticular cartilage: covers epiphysisPeriosteum: bone covering (pain sensitive)Sharpey’s fibers: periosteum attaches to underlying boneMedullary cavity: Hollow chamber in bone- red marrow produces blood cells- yellow marrow is adiposeEndosteum: thin layer lining the medullary cavity
6BLOOD AND NERVE SUPPLY OF BONE Bone is supplied with blood by:Periosteal arteries accompanied by nerves supply the periosteum and compact boneEpiphyseal veins carry blood away from long bonesNerves accompany the blood vessels that supply bonesThe periosteum is rich in sensory nerves sensitive to tearing or tension
7LONG BONES Compact Bone – dense outer layer Spongy Bone – (cancellous bone) honeycomb of trabeculae (needle-like or flat pieces) filled with bone marrow
8COMPACT BONE: (OSTEON) EXTERNAL LAYER - called lamellar bone (groups ofelongated tubules called lamella)- majority of all long bones- protection and strength(wt. bearing)- concentric ring structure- blood vessels and nerves penetrateperiosteum through horizontalopenings called perforating(Volkmann’s) canals.
9COMPACT BONE: (OSTEON) EXTERNAL LAYER Central (Haversian) canals run longitudinally. Blood vessels and nerves.- around canals are concentric lamella- osteocytes occupy lacunae which are between the lamella- radiating from the lacunea are channels called canaliculi (finger likeprocesses of osteocytes)
10COMPACT BONE Lacunae are connected to one another by canaliculi Osteon contains: - central canal- surrounding lamellae- lacunae- osteocytes- canaliculi
11SPONGY BONE (CANCELLOUS BONE): INTERNAL LAYER - trabecular bone tissue (haphazard arrangement).- filled with red and yellow bone marrow- osteocytes get nutrients directly from circulating blood.- short, flat and irregular bone is made up of mostly spongy bone
12HISTOLOGY OF BONE Histology of bone tissue Cells are surrounded by matrix.- 25% water- 25% protein- 50% mineral salts4 cell types make up osseous tissueOsteoprogenitor cellsOsteoblastsOsteocytesOsteoclasts
13Osteoprogenitor cells: - derived from mesenchyme- all connective tissue is derived- unspecialized stem cells- undergo mitosis and developinto osteoblasts- found on inner surface ofperiosteum and endosteum.
14Osteoblasts:- bone forming cells- found on surface of bone (arrow)- no ability to mitotically divide- collagen secretorsOsteocytes:- mature bone cells- derived form osteoblasts- do not secrete matrix material- cellular duties include exchange of nutrients and waste with blood.
15Osteoclasts- bone resorbing cells- bone surface- growth, maintenance and bone repairAbundant inorganic mineral salts:Tricalcium phosphate in crystallineform called hydroxyapatiteCa3(PO4)2(OH)2Calcium Carbonate: CaCO3Magnesium Hydroxide: Mg(OH)2Fluoride and Sulfate
16SKELETAL CARTILAGE Chondrocytes: cartilage producing cells. Lacunae: small cavities where thechondrocytes are encased.Extracellular matrix: jellylike groundsubstance.Perichondrium: layer of dense irregularconnective tissue that surrounds thecartilage.No blood vessels or nerves
17Types of Cartilage Hyaline cartilage – (glassy) Most abundant cartilageProvides support through flexibilityArticular cartilages and costal cartilage, larynx, trachea, and noseElastic cartilage – contains many elastic fibersAble to tolerate repeated bendingEar and epiglottisFibrocartilage – resists strong compression and strong tensionAn intermediate between hyaline and elastic cartilageIntervertebral discs and pubic symphysis
18BONE FORMATION The process of bone formation is called ossification Bone formation occurs in four situations:1) Formation of bone in an embryo2) Growth of bones until adulthood3) Remodeling of bone4) Repair of fractures
19Bone Formation Formation of Bone in an Embryo cartilage formation and ossification occurs during the sixth week of embryonic developmenttwo patternsIntramembranous ossificationFlat bones of the skull and mandible are formed in this way“Soft spots” that help the fetal skull pass through the birth canal later become ossified forming the skullEndochondral ossificationThe replacement of cartilage by boneMost bones of the body are formed in this way including long bones
20Intramembranous Ossification An ossification center appears in the fibrous connective tissue membraneOsteoblasts secrete bone matrix within the fibrous membraneOsteoblasts mature into osteocytes
21Endochondral Ossification Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.Blood vessels invade the epiphyses and osteo-blasts form secondary centers of ossification.ArticularcartilageEnlargingchondrocytes withincalcifying matrixEpiphysisEpiphysealcartilageMarrowcavityDiaphysisMarrowcavityPrimaryossificationcenterSecondaryossificationcenterBloodvesselBoneformationBloodvesselCartilagemodelReplacement of hyaline cartilage with boneMost bones are formed this way (i.e. long bones).
22Longitudinal Bone Growth Longitudinal Growth (interstitial) – cartilage continually grows and is replaced by boneBones lengthen entirely by growth of the epiphyseal platesCartilage is replaced with bone as quickly as it growsEpiphyseal plate maintains constant thickness
23GROWTH IN LENGTHThe growth in length of long bones involves two major events:Growth of cartilage on the epiphyseal plateReplacement of cartilage by bone tissue in the epiphyseal plate- osteoblasts located beneath theperiosteum secrete bone matrix andbuild bone on the surface- osteoclasts located in the endosteumresorbs (breakdown) bone.
24GROWTH OF CARTILAGE ON THE EPIPHYSEAL PLATE - epiphyseal plate (bone length)- 4 zones of bone growth under hGH.1- Zone of resting cartilage (quiescent):- no bone growth- located near the epiphyseal plate- scattered chondrocytes- anchors plate to bone2- Zone of proliferating cartilage (prolferation zone)- chondrocytes stacked like coins- chondrocytes divide
25- large chondrocytes arranged in columns 3- Zone of hypertrophic (maturing) cartilage- large chondrocytes arranged in columns- lengthwise expansion of epiphyseal plate4- Zone of calcified cartilage- few cell layers thick- occupied by osteoblasts and osteoclastsand capillaries from the diaphysis- cells lay down bone- dead chondrocytes surrounded by a calcifiedmatrix.Matrix resembles long spicules of calcifiedcartilage.Spicules are partly eroded by osteoclasts and thencovered in bone matrix from osteoblasts: spongybone is formed.
26APPOSITIONAL BONE GROWTH Growing bones widen as they lengthenAppositional growth – growth of a bone by addition of bone tissue to its surfaceBone is resorbed at endosteal surface and added at periosteal surfaceOsteoblasts – add bone tissue to the external surface of the diaphysisOsteoclasts – remove bone from the internal surface of the diaphysisFigure 6-6
27BONE REMODELING - bone continually renews itself - never metabolically at rest- enables Ca to be pulled from bone when blood levels are low- osteoclasts are responsible for matrix destruction- produce lysosomal enzymes and acids- spongy bone replaced every 3-4 years- compact bone every 10 years
28Fractures: Any bone break. - blood clot will form around break- fracture hematoma- inflammatory process begins- blood capillaries grow into clot- phagocytes and osteoclastsremove damaged tissue- procallus forms and is invaded byosteoprogenitor cells andfibroblasts- collagen and fibrocartilage turnsprocallus to fibrocartilagenous(soft) callus
29broken ends of bone are bridged by callus osteoprogenitor cells are replaced byosteoblasts and form spongy bonebony (hard) callus is formedcallus is resorbed by osteoclasts and compact bone replaces spongy bone.Remodeling : the shaft is reconstructed to resemble original unbroken bone.Closed reduction - bone ends coaxed back into place by manipulationOpen reduction - surgery, bone ends secured together with pins or wires