Presentation on theme: "Skeletal System: Bones and Bone Tissue"— Presentation transcript:
1 Skeletal System: Bones and Bone Tissue Chapter 6Skeletal System: Bones and Bone Tissue
2 Functions of the Skeletal System Support. Bone is hard and rigid; cartilage is flexible yet strong. Cartilage in nose, external ear, thoracic cage and trachea. Ligaments- bone to boneProtection. Skull around brain; ribs, sternum, vertebrae protect organs of thoracic cavityMovement. Produced by muscles on bones, via tendons. Ligaments allow some movement between bones but prevent excessive movement (joint: formed where two or more bones come together------allows movement between bones)Storage. Ca and P. Stored then released as needed. Fat stored in marrow cavitiesBlood cell production. Bone marrow that gives rise to blood cells and platelets
3 Components of Skeletal System BoneCartilage: three typesHyalineFibrocartilageElasticTendons and ligaments (Tendons: muscle to boneLigament: bone to bone)
4 Hyaline Cartilage Consists of specialized cells that produce matrix Chondroblasts: form matrixChondrocytes: surrounded by matrix; are lacunaeMatrix. Collagen fibers for strength, proteoglycans for resiliencyPerichondrium. Double-layered C.T. sheath. Covers cartilage except at articulationsInner. More delicate, has fewer fibers, contains chondroblastsOuter. Blood vessels and nerves penetrate. No blood vessels in cartilage itselfArticular cartilage. Covers bones at joints; has no perichondriumGrowthAppositional. New chondrocytes and new matrix at the periphery(chondroblasts in perichondrium lay down new matrix & new chondrocytes)Interstitial. Chondrocytes within the tissue divide and add more matrix between the cells.
5 Bone HistologyBone matrix. Like reinforced concrete. Steel bars is collagen fibers, cement is hydroxyapatiteOrganic: collagen and proteoglycans (35%)Inorganic: hydroxyapatite. CaPO4 crystals (65%)If mineral removed, bone is too bendableIf collagen removed, bone is too brittle
6 Bone Histology Bone cells OsteoblastsOsteocytesOsteoclastsStem cells or osteochondral progenitor cellsWoven bone: collagen fibers randomly orientedLamellar bone: mature bone in sheetsCancellous bone (spongy): contain trabeculae-less bone matrix & more spaceCompact bone: dense-more bone matrix & less space
7 Bone Cells Osteoblasts Formation of bone through ossification or osteogenesis. Collagen produced by E.R. and golgi. Released by exocytosis. Precursors of hydroxyapetite stored in vesicles, then released by exocytosis.Ossification: formation of bone by osteoblasts. It occurs by appositional growth on surface of previously existing bone. Osteoblasts communicate through gap junctions. Bone matrix produced by osteoblasts covers the older bone & surrounds osteoblasts results in new layer of bone.
8 Bone CellsOsteocytes. Mature bone cells once surrounded by matrix. They are relatively inactive, but can make small amounts of matrix to maintain it.Lacunae: spaces occupied by osteocyte cell bodyCanaliculi: canals occupied by osteocyte cell processesNutrients diffuse through tiny amount of liquid surrounding cell and filling lacunae and canaliculi. Then can transfer nutrients from one cell to the next through gap junctions.
9 Bone CellsOsteoclasts. Responsible for resorption of bone (breakdown of bone)Ruffled border (projections): where cell membrane borders bone and resorption is taking place.H ions pumped across membrane, acid forms, eats away bone.Release enzymes that digest the bone.Derived from monocytes (which are formed from stem cells in red bone marrow)MultinucleatedStem Cells. Mesenchyme (Osteochondral Progenitor Cells) become chondroblasts or osteoblasts. (Remember: osteocytes derived from osteoblasts)
10 Woven and Lamellar Bone Woven bone. Collagen fibers randomly oriented.- first formed during fetal development or repair of fracture- after formation, osteoclasts break down woven bone & osteoblasts build new matrix this process called remodelingRemodelingRemoving old bone and adding newWoven bone is remodeled into lamellar boneLamellar boneMature bone in sheets called lamellae. Fibers are oriented in one direction in each layer, but in different directions in different layers for strength.
11 Cancellous (Spongy) Bone Trabeculae: interconnecting rods or plates of bone. Like scaffolding.Spaces filled with marrow & blood vessels.Covered with endosteum.Oriented along stress linesTrabeculae consist of several lamellae (thin sheets) w/ osteocytes located in lacunae between them
12 Compact Bone Central or Haversian canals: parallel to long axis Lamellae: thin sheets/layersconcentric (circles), circumferential (perimeter, periphery), interstitial (between osteon)Osteon or Haversian system: central canal (also called haversian canals------contains blood vessels that run parallel to long axis of bone), associated concentric lamellae and osteocytesPerforating or Volkmann’s canal: perpendicular to long axis. Both perforating and central canals contain blood vessels. Central canals receive blood vessels from perforating canals & nutrients in blood enter central canals, pass into canaliculi, move through osteocytes to osteocytes (by gap junctions). Waste removed in reverse direction.
13 Bone Shapes Long Ex. Upper and lower limbs Short Ex. Carpals and tarsalsFlatEx. Ribs, sternum, skull, scapulaeIrregularEx. Vertebrae, facial
14 Structure of a Long Bone DiaphysisShaftCompact boneEpiphysisEnd of the boneCancellous boneEpiphyseal plate: growth plate (separates epiphysis from diaphysis)Hyaline cartilage; present until growth stopsEpiphyseal line: bone stops growing in length (epiphyseal plate becomes epiphyseal line)Medullary cavity (space): In children medullary cavity is red marrow, gradually changes to yellow in limb bones and skull (except for epiphyses of long bones). Rest of skeleton is red.
15 Structure of a Long Bone, cont. PeriosteumOuter is fibrous (contains blood vessels & nerves)Inner is single layer of bone cells including osteoblasts, osteoclasts and osteochondral progenitor cellsTendons & ligaments attach to bone & become continuous with fibers of periosteum.Sharpey’s fibers: some collagen fibers of tendons or ligaments penetrate the periosteum and into the bone. Strengthen attachment of tendon or ligaments to bone.Endosteum. Similar to periosteum, but more cellular. Lines all internal surfaces of all cavities including spaces in cancellous bone.
16 Structure of Flat, Short, and Irregular Bones Flat BonesNo diaphyses, epiphysesSandwich of cancellous between compact boneShort and Irregular BoneCompact bone that surrounds cancellous bone center; similar to structure of epiphyses of long bones (bec. have processes that possess epiphyseal growth platesNo diaphyses and not elongatedSome flat and irregular bones of skull have sinuses (air filled spaces) lined by mucous membranes.
17 Bone Development Intramembranous ossification Takes place in connective tissue membraneEndochondral ossificationTakes place in cartilageBoth methods of ossificationProduce woven bone that is then remodeledAfter remodeling, formation cannot be distinguished as one or other