2 Skeletal System: Bones and Bone Tissue Chapter 6Skeletal System: Bones and Bone Tissue
3 Skeletal System Functions 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 movementStorage. 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
4 Components of Skeletal System BoneCartilage: three typesHyalineFibrocartilageElastic
5 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 peripheryInterstitial. Chondrocytes within the tissue divide and add more matrix between the cells.
6 Bone Shapes Long Ex. Upper and lower limbs Short Ex. Carpals and tarsalsFlatEx. Ribs, sternum, skull, scapulaeIrregularEx. Vertebrae, facial
7 Long Bone Structure Diaphysis Shaft Compact bone Epiphysis End of the boneCancellous boneEpiphyseal plate: growth plateHyaline cartilage; present until growth stopsEpiphyseal line: bone stops growing in lengthMedullary cavity: 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.Red marrowYellow marrow
8 Long Bone Structure, cont. PeriosteumOuter is fibrousInner is single layer of bone cells including osteoblasts, osteoclasts and osteochondral progenitor cellsFibers of tendon become continuous with fibers of periosteum.Sharpey’s fibers: some periosteal fibers penetrate through the periosteum and into the bone. Strengthen attachment of tendon to bone.Endosteum. Similar to inner layer of periosteum. Lines all internal spaces including spaces in cancellous bone.Long Bone Structure, cont.
9 Flat, Short, 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 bonesNo diaphyses and not elongatedSome flat and irregular bones of skull have sinuses lined by mucous membranes.
10 Bone HistologyBone matrix. Like reinforced concrete. Rebar is collagen fibers, cement is hydroxyapetiteOrganic: collagen and proteoglycansInorganic: hydroxyapetite. CaPO4 crystalsBone cells (see following slides for particulars)OsteoblastsOsteocytesOsteoclastsStem cells or osteochondral progenitor cellsWoven bone: collagen fibers randomly orientedLamellar bone: mature bone in sheetsCancellous bone: trabeculaeCompact bone: dense
11 Bone Matrix If mineral removed, bone is too bendable If collagen removed, bone is too brittle
12 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. Osteoblasts communicate through gap junctions. Cells surround themselves by matrix.Bone Cells
13 OsteocytesOsteocytes. Mature bone cells. Stellate. Surrounded by matrix, 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.
14 Osteoclasts and Stem Cells Osteoclasts. Resorption of boneRuffled border: 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)Multinucleated and probably arise from fusion of a number of cellsStem Cells. Mesenchyme (Osteochondral Progenitor Cells) become chondroblasts or osteoblasts.
15 Woven and Lamellar Bone Woven bone. Collagen fibers randomly oriented.FormedDuring fetal developmentDuring fracture repairRemodelingRemoving 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.
16 Cancellous (Spongy) Bone Trabeculae: interconnecting rods or plates of bone. Like scaffolding.Spaces filled with marrow.Covered with endosteum.Oriented along stress lines
17 Compact Bone Central or Haversian canals: parallel to long axis Lamellae: concentric, circumferential, interstitialOsteon or Haversian system: central canal, contents, associated concentric lamellae and osteocytesPerforating or Volkmann’s canal: perpendicular to long axis. Both perforating and central canals contain blood vessels. Direct flow of nutrients from vessels through cell processes of osteoblasts and from one cell to the next.
18 Compact Bone Osteons (Haversian systems) Blood vessel-filled central canal (Haversian canal)Concentric lamellae of bone surround central canalLacunae and canaliculi contain osteocytes and fluidCircumferential lamellae on the periphery of a boneInterstitial lamellae between osteons. Remnants of osteons replaced through remodelingCompact Bone
19 Circulation in BonePerforating canals: blood vessels from periosteum penetrate boneVessels of the central canalNutrients and wastes travel to and from osteocytes viaInterstitial fluid of lacunae and canaliculiFrom osteocyte to osteocyte by gap junctions
20 Bone Development: Two Types Intramembranous ossificationTakes 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
21 Intramembranous Ossification Takes place in connective tissue membrane formed from embryonic mesenchymeForms many skull bones, part of mandible, diaphyses of claviclesWhen remodeled, indistinguishable from endochondral bone.Centers of ossification: locations in membrane where ossification beginsFontanels: large membrane-covered spaces between developing skull bones; unossified
23 Endochondral Ossification Bones of the base of the skull, part of the mandible, epiphyses of the clavicles, and most of remaining bones of skeletal systemCartilage formation begins at end of fourth week of developmentSome ossification beginning at about week eight; some does not begin until years of age
27 Growth in Bone Length Appositional growth only Interstitial growth cannot occur because matrix is solidOccurs on old bone and/or on cartilage surfaceGrowth in length occurs at the epiphyseal plateInvolves the formation of new cartilage byInterstitial cartilage growthAppositional growth on the surface of the cartilageClosure of epiphyseal plate: epiphyseal plate is ossified becoming the epiphyseal line. Between 12 and 25 years of ageArticular cartilage: does not ossify, and persists through life
33 Factors Affecting Bone Growth Size and shape of a bone determined genetically but can be modified and influenced by nutrition and hormonesNutritionLack of calcium, protein and other nutrients during growth and development can cause bones to be smallVitamin DNecessary for absorption of calcium from intestinesCan be eaten or manufactured in the bodyRickets: lack of vitamin D during childhoodOsteomalacia: lack of vitamin D during adulthood leading to softening of bonesVitamin CNecessary for collagen synthesis by osteoblastsScurvy: deficiency of vitamin CLack of vitamin C also causes wounds not to heal, teeth to fall out
34 Factors Affecting Bone Growth, cont. HormonesGrowth hormone from anterior pituitary. Stimulates interstitial cartilage growth and appositional bone growthThyroid hormone required for growth of all tissuesSex hormones such as estrogen and testosteroneCause growth at puberty, but also cause closure of the epiphyseal plates and the cessation of growth
35 Bone Remodeling Converts woven bone into lamellar bone Involved in bone growth, changes in bone shape, adjustments in bone due to stress, bone repair, and Ca ion regulationRelative thickness of bone changes as bone grows. Bone constantly removed by osteoclasts and new bone formed by osteoblasts.Formation of new osteons in compact boneOsteoclasts enter the osteon from blood in the central canal and internally remove lamellae. Osteoblasts replace boneOsteoclasts remove bone from the exterior and the bone is rebuilt
36 Bone RepairHematoma formation. Localized mass of blood released from blood vessels but confined within an organ or space. Clot formation.Callus formation. Callus: mass of tissue that forms at a fracture site and connects the broken ends of the bone.Internal- blood vessels grow into clot in hematoma.Macrophages clean up debris, osteoclasts break down dead tissue, fibroblasts produce collagen and granulation tissue.Chondroblasts from osteochondral progenitor cells of periosteum and endosteum produce cartilage within the collagen.Osteoblasts invade. New bone is formed.External- collar around opposing ends. Periosteal osteochondral progenitor cells osteoblasts and chondroblasts. Bone/cartilage collar stabilizes two pieces.
37 Bone Repair, cont.Callus ossification. Callus replaced by woven, cancellous bone4. Bone remodeling. Replacement of cancellous bone and damaged material by compact bone. Sculpting of site by osteoclasts
38 Calcium Homeostasis Bone is major storage site for calcium The level of calcium in the blood depends upon movement of calcium into or out of bone.Calcium enters bone when osteoblasts create new bone; calcium leaves bone when osteoclasts break down boneTwo hormones control blood calcium levels- parathyroid hormone and calcitonin.
40 Effects of Aging on Skeletal System Bone matrix decreases. More brittle due to lack of collagen; but also less hydroxyapetite.Bone mass decreases. Highest around 30. Men denser due to testosterone and greater weight. African Americans and Hispanics have higher bone masses than Caucasians and Asians. Rate of bone loss increases 10 fold after menopause. Cancellous bone lost first, then compact.Increased bone fracturesBone loss causes deformity, loss of height, pain, stiffnessStooped postureLoss of teeth
41 Open (compound)- bone break with open wound Open (compound)- bone break with open wound. Bone may be sticking out of wound.Closed (simple)- Skin not perforated.Incomplete- doesn’t extend across the bone. Complete- doesGreenstick: incomplete fracture that occurs on the convex side of the curve of a boneHairline: incomplete where two sections of bone do not separate. Common in skull fracturesComminuted fractures: complete with break into more than two piecesBone Fractures
42 Bone Fractures, cont.Impacted fractures: one fragment is driven into the cancellous portion of the other fragment.Classified on basis of direction of fractureLinearTransverseSpiralObliqueDentate: rough, toothed, broken endsStellate radiating out from a central point.