Download to read offline
More Related Content
Bone new-48
- 1.
- 4. BoneBone Bone isthe main component of theBone is the main component of the skeleton in the adult human. Likeskeleton in the adult human. Like cartilage, bone is a specialised formcartilage, bone is a specialised form of dense connective tissue. Boneof dense connective tissue. Bone gives the skeleton the necessarygives the skeleton the necessary rigidity to function as attachmentrigidity to function as attachment and lever for muscles and supportsand lever for muscles and supports the body against gravity.the body against gravity.
- 5. Bone Cell LineagesBoneCell Lineages Paraxial MesodermParaxial Mesoderm • SomiteSomite sclerotomesclerotome • osteoprogenitor cellsosteoprogenitor cells osteoblastsosteoblasts osteocytesosteocytes stem cells (bone lining cells)stem cells (bone lining cells) Bone Marrow (pluripotential stem cell)Bone Marrow (pluripotential stem cell) • monocytesmonocytes osteoclastsosteoclasts
- 6. Specialized Cells ofBoneSpecialized Cells of Bone Osteoprogenitor cells: stem cell of bone tissue,Osteoprogenitor cells: stem cell of bone tissue, resides in the periosteum and endosteum.resides in the periosteum and endosteum. Osteoblasts: cannot divide, makes calcified boneOsteoblasts: cannot divide, makes calcified bone matrix (osteoid tissue), found in endosteum.matrix (osteoid tissue), found in endosteum. Oteocytes: mature bone cell inside a lacuna,Oteocytes: mature bone cell inside a lacuna, maintains bone matrix with canalicli.maintains bone matrix with canalicli. Osteoclasts: dissolves bone matrix to liberateOsteoclasts: dissolves bone matrix to liberate Ca2+ and change shape of (remodel) bone.Ca2+ and change shape of (remodel) bone.
- 7. Bone MatrixBone Matrix Theorganic matrix of bone consists of:The organic matrix of bone consists of: 95% Type I collagen95% Type I collagen 5% proteoglycans and5% proteoglycans and noncollagenous proteins (osteopontinnoncollagenous proteins (osteopontin and osteocalcin).and osteocalcin).
- 8. Constituents of BoneTissueConstituents of Bone Tissue OrganicOrganic ComponentsComponents (1/3)(1/3) Collagen FibersCollagen Fibers Specialized BoneSpecialized Bone CellsCells GlycosaminoglycanGlycosaminoglycan s (GAGs)s (GAGs) FlexibiltyFlexibilty InorganicInorganic ComponentsComponents (2/3)(2/3) CalciumCalcium HydroxyapatiteHydroxyapatite (80%) (Ca and P)(80%) (Ca and P) Calcium CarbonateCalcium Carbonate (15%) Other trace(15%) Other trace minerals (Mg, Na)minerals (Mg, Na) RigidityRigidity
- 9. Two types ofbone can be distinguishedTwo types of bone can be distinguished macroscopicallymacroscopically:: Trabecular boneTrabecular bone Compact boneCompact bone
- 10. Trabecular boneTrabecular bone •Trabecular boneTrabecular bone (also called(also called cancellous or spongy bone) consistscancellous or spongy bone) consists of delicate bars and sheets of bone,of delicate bars and sheets of bone, trabeculaetrabeculae, which branch and, which branch and intersect to form a sponge likeintersect to form a sponge like network. The ends of long bones (ornetwork. The ends of long bones (or epiphysesepiphyses) consist mainly of) consist mainly of trabecular bone.trabecular bone.
- 11. Compact boneCompact bone Compact boneCompact bone does not have anydoes not have any spaces or hollows in the bone matrixspaces or hollows in the bone matrix that are visible to the eye. Compactthat are visible to the eye. Compact bone forms the thick-walled tube ofbone forms the thick-walled tube of the shaft (orthe shaft (or diaphysisdiaphysis) of long) of long bones, which surrounds the marrowbones, which surrounds the marrow cavity (orcavity (or medullary cavitymedullary cavity). A thin). A thin layer of compact bone also coverslayer of compact bone also covers the epiphyses of long bones.the epiphyses of long bones.
- 13. Bone is,again like cartilage, surroundedBone is, again like cartilage, surrounded by a layer of dense connective tissue, theby a layer of dense connective tissue, the periosteumperiosteum. A thin layer of cell-rich. A thin layer of cell-rich connective tissue, theconnective tissue, the endosteumendosteum, lines, lines the surface of the bone facing the marrowthe surface of the bone facing the marrow cavity. Both the periosteum and thecavity. Both the periosteum and the endosteum possessendosteum possess osteogenic potencyosteogenic potency.. Following injury, cells in these layers mayFollowing injury, cells in these layers may differentiate intodifferentiate into osteoblastsosteoblasts (bone(bone forming cells) which become involved informing cells) which become involved in the repair of damage to the bone.the repair of damage to the bone.
- 15. Histological Organisation ofHistologicalOrganisation of BoneBone Compact BoneCompact Bone Compact bone consists almost entirely of extracellularCompact bone consists almost entirely of extracellular substance, thesubstance, the matrixmatrix. Osteoblasts deposit the matrix. Osteoblasts deposit the matrix in the form of thin sheets which are calledin the form of thin sheets which are called lamellaelamellae.. Lamellae areLamellae are microscopicalmicroscopical structures. Collagen fibresstructures. Collagen fibres within each lamella run parallel to each other. Collagenwithin each lamella run parallel to each other. Collagen fibres which belong to adjacent lamellae run at obliquefibres which belong to adjacent lamellae run at oblique angles to each other. Fibre density seems lower at theangles to each other. Fibre density seems lower at the border between adjacent lamellae, which gives rise toborder between adjacent lamellae, which gives rise to the lamellar appearance of the tissue. Bone which isthe lamellar appearance of the tissue. Bone which is composed by lamellae when viewed under thecomposed by lamellae when viewed under the microscope is also calledmicroscope is also called lamellar bonelamellar bone..
- 16. In theprocess of the deposition of theIn the process of the deposition of the matrix, osteoblasts become encased inmatrix, osteoblasts become encased in small hollows within the matrix, thesmall hollows within the matrix, the lacunaelacunae. Unlike chondrocytes, osteocytes. Unlike chondrocytes, osteocytes have several thin processes, which extendhave several thin processes, which extend from the lacunae into small channelsfrom the lacunae into small channels within the bone matrix , thewithin the bone matrix , the canaliculicanaliculi.. Canaliculi arising from one lacuna mayCanaliculi arising from one lacuna may anastomose with those of other lacunaeanastomose with those of other lacunae and, eventually, with larger, vessel-and, eventually, with larger, vessel- containing canals within the bone.containing canals within the bone. Canaliculi provide the means for theCanaliculi provide the means for the osteocytes to communicate with eachosteocytes to communicate with each other and to exchange substances byother and to exchange substances by diffusion.diffusion.
- 17. In maturecompact bone most of theIn mature compact bone most of the individual lamellae form concentric ringsindividual lamellae form concentric rings around larger longitudinal canals (approx.around larger longitudinal canals (approx. 50 µm in diameter) within the bone50 µm in diameter) within the bone tissue. These canals are calledtissue. These canals are called HaversianHaversian canalscanals. Haversian canals typically run. Haversian canals typically run parallel to the surface and along the longparallel to the surface and along the long axis of the bone. The canals and theaxis of the bone. The canals and the surrounding lamellae (8-15) are called asurrounding lamellae (8-15) are called a Haversian systemHaversian system or anor an osteonosteon. A. A Haversian canal generally contains one orHaversian canal generally contains one or two capillaries and nerve fibres.two capillaries and nerve fibres.
- 18. Irregular areasofIrregular areas of interstitial lamellaeinterstitial lamellae,, which apparently do not belong to anywhich apparently do not belong to any Haversian system, are found in betweenHaversian system, are found in between the Haversian systems. Immediatelythe Haversian systems. Immediately beneath the periosteum and endosteumbeneath the periosteum and endosteum a few lamella are found which runa few lamella are found which run parallel to the inner and outer surfacesparallel to the inner and outer surfaces of the bone. They are theof the bone. They are the circumferentialcircumferential lamellaelamellae andand endosteal lamellaeendosteal lamellae..
- 19. A secondsystem of canals, calledA second system of canals, called Volkmann's canalsVolkmann's canals, penetrates the, penetrates the bone more or less perpendicular tobone more or less perpendicular to its surface. These canals establishits surface. These canals establish connections of the Haversian canalsconnections of the Haversian canals with the inner and outer surfaces ofwith the inner and outer surfaces of the bone. Vessels in Volkmann'sthe bone. Vessels in Volkmann's canals communicate with vessels incanals communicate with vessels in the Haversian canals on the onethe Haversian canals on the one hand and vessels in the endosteumhand and vessels in the endosteum on the other. A few communicationson the other. A few communications also exist with vessels in thealso exist with vessels in the periosteum.periosteum.
- 20. Trabecular BoneTrabecular Bone The matrix of trabecular bone is alsoThe matrix of trabecular bone is also deposited in the form of lamellaedeposited in the form of lamellae. In. In mature bones, trabecular bone will also bemature bones, trabecular bone will also be lamellar bone. However,lamellar bone. However, lamellae inlamellae in trabecular bone do not form Haversiantrabecular bone do not form Haversian systemssystems. Lamellae of trabecular bone are. Lamellae of trabecular bone are deposited on preexisting trabeculaedeposited on preexisting trabeculae depending on the local demands on bonedepending on the local demands on bone rigidity.rigidity. Osteocytes, lacunae and canaliculi inOsteocytes, lacunae and canaliculi in trabecular bone resemble those intrabecular bone resemble those in compact bone.compact bone.
- 21. Lamellar boneLamellar bone ** Note the distinction betweenNote the distinction between macroscopic (visible to the eye)macroscopic (visible to the eye) and microscopic (only visibleand microscopic (only visible under the microscope)under the microscope) appearance when the bone isappearance when the bone is namednamed. Lamellar bone forms both. Lamellar bone forms both trabecular bone and compact bone,trabecular bone and compact bone, which are the two macroscopicallywhich are the two macroscopically recognizable bone forms.recognizable bone forms.
- 23. Compact bone,human - Schmorl stainCompact bone, human - Schmorl stain Lamellae which run parallel to the surface of the bone are visible both onLamellae which run parallel to the surface of the bone are visible both on the outer, convex surface of the bone (circumferential lamellae) and onthe outer, convex surface of the bone (circumferential lamellae) and on the inner, concave surface of the bone facing the marrow cavitythe inner, concave surface of the bone facing the marrow cavity (endosteal lamellae). The surface formed by the endosteal lamellae is(endosteal lamellae). The surface formed by the endosteal lamellae is often more irregular than the surface formed by the circumferentialoften more irregular than the surface formed by the circumferential lamellae. The space between these two sets of lamellae is filled bylamellae. The space between these two sets of lamellae is filled by Haversian systems and interstitial lamellae. Only few of the HaversianHaversian systems and interstitial lamellae. Only few of the Haversian systems are "textbook" circular. Osteocyte lacunae are visible betweensystems are "textbook" circular. Osteocyte lacunae are visible between the lamellae. Canaliculi become visible at high magnificationthe lamellae. Canaliculi become visible at high magnification
- 26. Compact bone,human - ground (unstained)Compact bone, human - ground (unstained) The osteocyte lacunae are the main feature of the ground section.The osteocyte lacunae are the main feature of the ground section. They are visible as elongated black spots in the bone matrix.They are visible as elongated black spots in the bone matrix. Canaliculi, radiate from the lacunae into the surrounding boneCanaliculi, radiate from the lacunae into the surrounding bone matrix. Some lamellae are visible in the ground section. There ismatrix. Some lamellae are visible in the ground section. There is actually no distinct border between most lamellae, but our brainactually no distinct border between most lamellae, but our brain can use the elongated osteocyte lacunae and their orientation tocan use the elongated osteocyte lacunae and their orientation to "reconstruct" the lamellae. Volkman's canals connect to a few of"reconstruct" the lamellae. Volkman's canals connect to a few of the Haversian canals.the Haversian canals.
- 29. Articular cartilage,bovine - H&EArticular cartilage, bovine - H&E Thin sheets and bars of bone, trabeculae, are visible at lowThin sheets and bars of bone, trabeculae, are visible at low magnification. Although they may appear as individual pieces inmagnification. Although they may appear as individual pieces in sections, they form an interconnected meshwork in the living bone.sections, they form an interconnected meshwork in the living bone. The spaces between the trabeculae, the marrow cavity of theThe spaces between the trabeculae, the marrow cavity of the epiphysis, is filled by either red bone marrow or yellow bone marrow.epiphysis, is filled by either red bone marrow or yellow bone marrow. At high magnification, elongated osteocyte lacunae, which in wellAt high magnification, elongated osteocyte lacunae, which in well preserved tissue still contain osteocytes, are visible in the matrix. Ifpreserved tissue still contain osteocytes, are visible in the matrix. If the H&E stain also turned out well, it should be visible that the matrixthe H&E stain also turned out well, it should be visible that the matrix of the trabecular bone is formed by lamellae. Canaliculi are presentof the trabecular bone is formed by lamellae. Canaliculi are present but hard to identify in most H&E stained sections. Haversian systemsbut hard to identify in most H&E stained sections. Haversian systems areare notnot present in the trabeculae.present in the trabeculae.
- 32. Bone Matrix andBone CellsBone Matrix and Bone Cells Bone MatrixBone Matrix Bone matrix consists of collagen fibres (about 90% of theBone matrix consists of collagen fibres (about 90% of the organicorganic substance) and ground substance. Collagen type Isubstance) and ground substance. Collagen type I is the dominant collagen form in bone. The hardness of theis the dominant collagen form in bone. The hardness of the matrix is due to its content of inorganic saltsmatrix is due to its content of inorganic salts (hydroxyapatite; about 75% of the dry weight of bone),(hydroxyapatite; about 75% of the dry weight of bone), which become deposited between collagen fibres.which become deposited between collagen fibres. Calcification begins a few days after the deposition ofCalcification begins a few days after the deposition of organic bone substance (ororganic bone substance (or osteoidosteoid) by the osteoblasts.) by the osteoblasts. Osteoblasts are capable of producing high localOsteoblasts are capable of producing high local concentration of calcium phosphate in the extracellularconcentration of calcium phosphate in the extracellular space, which precipitates on the collagen molecules. Aboutspace, which precipitates on the collagen molecules. About 75% of the hydroxyapatite is deposited in the first few days75% of the hydroxyapatite is deposited in the first few days of the process, butof the process, but complete calcification may take severalcomplete calcification may take several monthsmonths..
- 33. Bone CellsBone Cells Osteoprogenitor cellsOsteoprogenitor cells (or stem cells of bone)(or stem cells of bone) are located in the periosteum and endosteum.are located in the periosteum and endosteum. They are very difficult to distinguish from theThey are very difficult to distinguish from the surrounding connective tissue cells. Theysurrounding connective tissue cells. They differentiate intodifferentiate into OsteoblastsOsteoblasts (or bone forming(or bone forming cells).cells). Osteoblasts may form a low columnar "epitheloidOsteoblasts may form a low columnar "epitheloid layer" at sites of bone deposition. They containlayer" at sites of bone deposition. They contain plenty of rough endoplasmatic reticulum (collagenplenty of rough endoplasmatic reticulum (collagen synthesis) and a large Golgi apparatus. As theysynthesis) and a large Golgi apparatus. As they become trapped in the forming bone theybecome trapped in the forming bone they differentiate intodifferentiate into OsteocytesOsteocytes.. Osteocytes contain less endoplasmatic reticulumOsteocytes contain less endoplasmatic reticulum and are somewhat smaller than osteoblasts.and are somewhat smaller than osteoblasts.
- 34. OsteoclastsOsteoclasts are verylarge (up to 100 µm), multi-are very large (up to 100 µm), multi- nucleated (about 5-10 visible in anucleated (about 5-10 visible in a histological section, but up to 50 in thehistological section, but up to 50 in the actual cell) bone-resorbing cells. Theyactual cell) bone-resorbing cells. They arise by the fusion of monocytesarise by the fusion of monocytes (macrophage precursors in the blood) or(macrophage precursors in the blood) or macrophages. Osteoclasts attachmacrophages. Osteoclasts attach themselves to the bone matrix and formthemselves to the bone matrix and form a tight seal at the rim of the attachmenta tight seal at the rim of the attachment site. The cell membrane opposite thesite. The cell membrane opposite the matrix has deep invaginations forming amatrix has deep invaginations forming a ruffled borderruffled border. Osteoclasts empty the. Osteoclasts empty the contents of lysosomes into thecontents of lysosomes into the extracellular space between the ruffledextracellular space between the ruffled border and the bone matrix. The releasedborder and the bone matrix. The released enzymes break down the collagen fibresenzymes break down the collagen fibres of the matrix. Osteoclasts are stimulatedof the matrix. Osteoclasts are stimulated byby parathyroid hormoneparathyroid hormone (produced by(produced by the parathyroid gland) and inhibited bythe parathyroid gland) and inhibited by calcitonincalcitonin (produced by specialised cells(produced by specialised cells of the thyroid gland). Osteoclasts areof the thyroid gland). Osteoclasts are often seen within the indentations of theoften seen within the indentations of the bone matrix that are formed by theirbone matrix that are formed by their activity (activity (resorption baysresorption bays oror Howship'sHowship's lacunaelacunae).).
- 36. Formation of BoneFormationof Bone Bones are formed by twoBones are formed by two mechanisms:mechanisms: 1.1.intramembranousintramembranous ossificationossification (bones of the(bones of the skull, part of the mandibleskull, part of the mandible and clavicle) orand clavicle) or 2.2.endochondralendochondral
- 40. Intramembranous OssificationIntramembranous Ossification Intramembranous ossification occurs within aIntramembranous ossification occurs within a membranous, condensed plate of mesenchymal cells.membranous, condensed plate of mesenchymal cells. At the initial site of ossification (At the initial site of ossification (ossification centreossification centre)) mesenchymal cells (osteoprogenitor cells) differentiatemesenchymal cells (osteoprogenitor cells) differentiate into osteoblasts. The osteoblasts begin to deposit theinto osteoblasts. The osteoblasts begin to deposit the organic bone matrix, the osteoid. The matrix separatesorganic bone matrix, the osteoid. The matrix separates osteoblasts, which, from now on, are located in lacunaeosteoblasts, which, from now on, are located in lacunae within the matrix. The collagen fibres of the osteoidwithin the matrix. The collagen fibres of the osteoid form a woven network without a preferred orientation,form a woven network without a preferred orientation, andand lamellae are not present at this stagelamellae are not present at this stage. Because of. Because of the lack of a preferred orientation of the collagen fibresthe lack of a preferred orientation of the collagen fibres in the matrix, this type of bone is also calledin the matrix, this type of bone is also called wovenwoven bonebone. The osteoid calcifies leading to the formation of. The osteoid calcifies leading to the formation of primitive trabecular bone.primitive trabecular bone. Further deposition and calcification of osteoid at sitesFurther deposition and calcification of osteoid at sites where compact bone is needed leads to the formationwhere compact bone is needed leads to the formation of primitive compact bone.of primitive compact bone.
- 41. Intramembranous OssificationIntramembranous Ossification Mesoderm –> Mesenchymal cells –>Mesoderm –> Mesenchymal cells –> Osteoprogenitor cells –> OsteoblastsOsteoprogenitor cells –> Osteoblasts –> Oteocytes.–> Oteocytes.
- 42. ** Notethe distinction betweenNote the distinction between macroscopic and microscopic appearancemacroscopic and microscopic appearance when the bone is namedwhen the bone is named. We again have the. We again have the two macroscopically different forms of bone -two macroscopically different forms of bone - trabecular bone and compact bone - but theirtrabecular bone and compact bone - but their early developmental ("primitive") forms consistearly developmental ("primitive") forms consist of woven bone.of woven bone. Through subsequent reorganisation theThrough subsequent reorganisation the primitive compact and trabecular bone isprimitive compact and trabecular bone is converted into mature compact and trabecularconverted into mature compact and trabecular bone.bone. During reorganisation and growth, wovenDuring reorganisation and growth, woven bone will, in time, be replaced by lamellarbone will, in time, be replaced by lamellar bonebone.. Intramembranous ossification does not requireIntramembranous ossification does not require the existence of a cartilage bone modelthe existence of a cartilage bone model..
- 43. Mandible, intramembranousossificationMandible, intramembranous ossification - H&E- H&E The developing bone will in sections usuallyThe developing bone will in sections usually be associated with a number of other tissuesbe associated with a number of other tissues which develop in close association with it. Inwhich develop in close association with it. In case of the mandible, there can becase of the mandible, there can be developing teeth, the tongue, skin anddeveloping teeth, the tongue, skin and salivary glands.salivary glands. The first job - best done at low magnificationThe first job - best done at low magnification - is to find the developing bone. It should- is to find the developing bone. It should look like a coarse meshwork (trabecularlook like a coarse meshwork (trabecular bone) of pink tissue surrounding patches ofbone) of pink tissue surrounding patches of much lighter or unstained tissue. Lamellaemuch lighter or unstained tissue. Lamellae are not visible (woven bone) and the lacunaeare not visible (woven bone) and the lacunae are larger than lacunae in mature bone.are larger than lacunae in mature bone. Ossification centres appear as areas of aOssification centres appear as areas of a gradual transition from connective tissue togradual transition from connective tissue to bone. Light, pinkish bone matrix is foundbone. Light, pinkish bone matrix is found between the osteoblasts.between the osteoblasts. Depending on the state of development ofDepending on the state of development of the bone, it is occasionally possible to findthe bone, it is occasionally possible to find bone trabeculae which are lined by a layer ofbone trabeculae which are lined by a layer of osteoblasts. These osteblasts are depositingosteoblasts. These osteblasts are depositing the first lamellae on the already existingthe first lamellae on the already existing trabeculae. The trabeculae will thereforetrabeculae. The trabeculae will therefore have a core of woven bone, which ishave a core of woven bone, which is surrounded by lamellar bone. Compare thesurrounded by lamellar bone. Compare the shapes, sizes and frequencies of lacunae inshapes, sizes and frequencies of lacunae in lamellar and woven bone if both types oflamellar and woven bone if both types of bone are present.bone are present.
- 46. Endochondral OssificationEndochondral Ossification Most bones are formed by theMost bones are formed by the transformation of cartilage "bone models",transformation of cartilage "bone models", a process calleda process called endochondral ossificationendochondral ossification.. AA periosteal budperiosteal bud invades the cartilageinvades the cartilage model and allows osteoprogenitor cells tomodel and allows osteoprogenitor cells to enter the cartilage. At these sites, theenter the cartilage. At these sites, the cartilage is in a state of hypertrophy (verycartilage is in a state of hypertrophy (very large lacunae and chondrocytes) andlarge lacunae and chondrocytes) and partial calcification, which eventually leadspartial calcification, which eventually leads to the death of the chondrocytes.to the death of the chondrocytes.
- 47. Invading osteoprogenitorcellsInvading osteoprogenitor cells mature into osteoblasts, which usemature into osteoblasts, which use the framework of calcified cartilagethe framework of calcified cartilage to deposit new bone. The boneto deposit new bone. The bone deposited onto the cartilage scaffolddeposited onto the cartilage scaffold is lamellar bone. The initial site ofis lamellar bone. The initial site of bone deposition is called abone deposition is called a primaryprimary ossification centreossification centre. Secondary. Secondary ossification centres occur in theossification centres occur in the future epiphyses of the bone.future epiphyses of the bone. A thin sheet of bone, theA thin sheet of bone, the periostealperiosteal collarcollar, is deposited around the shaft, is deposited around the shaft of the cartilage model. The periostealof the cartilage model. The periosteal collar consists of woven bone.collar consists of woven bone.
- 48. Close to thezone of ossification, theClose to the zone of ossification, the cartilage can usually be divided into acartilage can usually be divided into a number of distinct zones :number of distinct zones : 1.1. A zone of chondrocyte proliferationA zone of chondrocyte proliferation containscontains longitudinal columns of mitotically activelongitudinal columns of mitotically active chondrocytes, which grow in size inchondrocytes, which grow in size in 2.2. the zone of cartilage maturation andthe zone of cartilage maturation and hypertrophy.hypertrophy. 3.3. A zone of cartilage calcificationA zone of cartilage calcification forms theforms the border between cartilage and the zone of boneborder between cartilage and the zone of bone deposition.deposition. 4.4. Reserve cartilageReserve cartilage, furthest away from the, furthest away from the zone of ossification, looks like immature hyalinezone of ossification, looks like immature hyaline cartilage.cartilage.
- 49. Primary and secondaryossificationPrimary and secondary ossification centrescentres Primary and secondary ossification centresPrimary and secondary ossification centres do not merge before adulthood. Betweendo not merge before adulthood. Between the diaphysis and the epiphyses a thinthe diaphysis and the epiphyses a thin sheet of cartilage, thesheet of cartilage, the epiphyseal plateepiphyseal plate, is, is maintained until adulthood.maintained until adulthood. By continuingBy continuing cartilage production, the epiphyseal platecartilage production, the epiphyseal plate provides the basis for rapid growth in theprovides the basis for rapid growth in the length of the bonelength of the bone. Cartilage production. Cartilage production gradually ceases in the epiphyseal plate asgradually ceases in the epiphyseal plate as maturity is approached. The epiphysealmaturity is approached. The epiphyseal plate is finally removed by the continuedplate is finally removed by the continued production of bone from the diaphysealproduction of bone from the diaphyseal side.side.
- 50. Bone formation andboneBone formation and bone resorptionresorption Bone formation and bone resorption goBone formation and bone resorption go hand in hand during the growth of bonehand in hand during the growth of bone.. This first deposited trabecular bone isThis first deposited trabecular bone is removed (By which cells?) as the zone ofremoved (By which cells?) as the zone of ossification moves in the direction of theossification moves in the direction of the future epiphyses. This process creates thefuture epiphyses. This process creates the marrow cavity of the bones.marrow cavity of the bones. Simultaneously, bone is removed from theSimultaneously, bone is removed from the endosteal surface and deposited on theendosteal surface and deposited on the periosteal surface of the compact boneperiosteal surface of the compact bone which forms the diaphysis. This results inwhich forms the diaphysis. This results in a growth of the diameter of the bone.a growth of the diameter of the bone.
- 51. Foetal vertebralcolumn, human - H&EFoetal vertebral column, human - H&E Hold the section against a light background. The cartilage models willHold the section against a light background. The cartilage models will stain very light, and the outlines of the skeletal structures they will formstain very light, and the outlines of the skeletal structures they will form can often be identified. If an ossification centre is present, it will appearcan often be identified. If an ossification centre is present, it will appear as a darker area within the cartilage model. The zonation of the cartilageas a darker area within the cartilage model. The zonation of the cartilage should be visible in all ossification centres. How much bone is presentshould be visible in all ossification centres. How much bone is present depends on how far ossification has proceeded. The newly formed bonedepends on how far ossification has proceeded. The newly formed bone trabeculae will often consist of lamellar bone with a more or lesstrabeculae will often consist of lamellar bone with a more or less extensive core of darkly staining calcified cartilage. The lamellarextensive core of darkly staining calcified cartilage. The lamellar organisation of the bone may not be visible.organisation of the bone may not be visible. How the ossification centre exactly will look also depends on the plane ofHow the ossification centre exactly will look also depends on the plane of the section in relation to the ossification centre.the section in relation to the ossification centre.
- 54. Growing bone,rabbit - H&EGrowing bone, rabbit - H&E The cartilage model has almostThe cartilage model has almost entirely been transformed into bone.entirely been transformed into bone. The only remaining cartilage is foundThe only remaining cartilage is found in the epiphyseal disk. Zones ofin the epiphyseal disk. Zones of cartilage proliferation, hypertrophycartilage proliferation, hypertrophy and calcification are visible at highand calcification are visible at high magnification, but only on one sidemagnification, but only on one side of the epiphyseal disk - towards theof the epiphyseal disk - towards the diaphysis, which increases in lengthdiaphysis, which increases in length as the cartilage generated by theas the cartilage generated by the epiphyseal disc is transformed intoepiphyseal disc is transformed into bone.bone. Osteoclasts may be found on theOsteoclasts may be found on the newly formed trabeculae ornewly formed trabeculae or associated with parts of the cartilageassociated with parts of the cartilage scaffold.scaffold.
- 56. Reorganisation and RestorationReorganisationand Restoration of Boneof Bone Changes in the size and shape ofChanges in the size and shape of bones during the period of growthbones during the period of growth imply some bone reorganisation.imply some bone reorganisation. Osteoblast and osteoclast constantlyOsteoblast and osteoclast constantly deposit and remove bone to adjustdeposit and remove bone to adjust its properties to growth-relatedits properties to growth-related demands on size and/or changes ofdemands on size and/or changes of tensile and compressive forces.tensile and compressive forces.
- 57. Although thereorganisation of bone may notAlthough the reorganisation of bone may not result in macroscopically visible changes ofresult in macroscopically visible changes of bone structure, it continues throughout life tobone structure, it continues throughout life to mend damage to bone (e.g. microfractures)mend damage to bone (e.g. microfractures) and to counteract the wear and tear occurringand to counteract the wear and tear occurring in bone. Osteoclasts and osteoblasts remain thein bone. Osteoclasts and osteoblasts remain the key players in this process. Osteoclasts "drill"key players in this process. Osteoclasts "drill" more or less circular tunnels within existingmore or less circular tunnels within existing bone matrix. Osteoblasts deposit new lamellaebone matrix. Osteoblasts deposit new lamellae of bone matrix on the walls of these tunnelsof bone matrix on the walls of these tunnels resulting in the formation of a new Haversianresulting in the formation of a new Haversian system within the matrix of compact bone.system within the matrix of compact bone. Parts of older Haversian systems, which mayParts of older Haversian systems, which may remain between the new ones, represent theremain between the new ones, represent the interstitial lamellae in mature bone. Capillariesinterstitial lamellae in mature bone. Capillaries and nerves sprout into new Haversian canals.and nerves sprout into new Haversian canals.
- 58. Restorative activitycontinues in aged humansRestorative activity continues in aged humans (about 2% of the Haversian systems seen in an(about 2% of the Haversian systems seen in an 84 year old individual contained lamellae that84 year old individual contained lamellae that had been formed within 2 weeks prior tohad been formed within 2 weeks prior to death!). However, the Haversian systems tenddeath!). However, the Haversian systems tend to be smaller in older individuals and the canalsto be smaller in older individuals and the canals are larger because of slower bone deposition. Ifare larger because of slower bone deposition. If these age-related changes in the appearance ofthese age-related changes in the appearance of the Haversian systems are pronounced they arethe Haversian systems are pronounced they are termedtermed osteopeniaosteopenia oror senile osteoporosissenile osteoporosis. The. The reduced strength of bone affected byreduced strength of bone affected by osteoporosis will increase the likelihood ofosteoporosis will increase the likelihood of fractures.fractures.
- 59. Bone FormationBone Formation This is aThis is a photomicrograph ofphotomicrograph of membranousmembranous developing of bone. (a)developing of bone. (a) indicates osteoblasts,indicates osteoblasts, while the nucleus to leftwhile the nucleus to left of (b) represents anof (b) represents an osteocyte. (c) is in theosteocyte. (c) is in the area of matrix secretedarea of matrix secreted by the osteoblasts,by the osteoblasts, while (d) is situated inwhile (d) is situated in surroundingsurrounding mesenchymal tissuemesenchymal tissue..
- 60. Electron Micrograph ofElectronMicrograph of OsteoblastOsteoblast This high magnificationThis high magnification electron micrograph of anelectron micrograph of an osteoblast demonstrates aosteoblast demonstrates a number of interestingnumber of interesting findings. A fairly wellfindings. A fairly well developed Golgi apparatusdeveloped Golgi apparatus is present (a), as is anis present (a), as is an extensive roughextensive rough endoplasmic reticulum (b).endoplasmic reticulum (b). The cell's nucleus (c) isThe cell's nucleus (c) is obvious as well. The areaobvious as well. The area marked (d) is an area ofmarked (d) is an area of collagen fiber matrixcollagen fiber matrix between the osteoblast andbetween the osteoblast and the bony trabecula (e).the bony trabecula (e).
- 61. Haversian Canal X-SectionHaversianCanal X-Section This photomicrographThis photomicrograph represnts a highrepresnts a high powered view of thepowered view of the central canal of acentral canal of a haversian system (orhaversian system (or osteon). (a) indicatesosteon). (a) indicates blood vessels, (b) isblood vessels, (b) is the endosteum, (c) isthe endosteum, (c) is the adjacent bonethe adjacent bone matrix, and (d)matrix, and (d) represents connectiverepresents connective tissue. (e) representstissue. (e) represents another view of aanother view of a lamella, similar to thatlamella, similar to that highlighted by (c).highlighted by (c).
- 62. Developing Long BoneDevelopingLong Bone This photomicrographThis photomicrograph illustrates the primaryillustrates the primary endochondral ossificationendochondral ossification center of a long bone. (a)center of a long bone. (a) represents the osteogenicrepresents the osteogenic bud, (b) is the hyalin cartligebud, (b) is the hyalin cartlige epiphysis, (d) highlightsepiphysis, (d) highlights surrounding mesenchymalsurrounding mesenchymal tissue, and (e) represents thetissue, and (e) represents the periosteum. (c) is theperiosteum. (c) is the subperiosteal bone collar,subperiosteal bone collar, staining black in this slidestaining black in this slide
- 63. OsteoblastsOsteoblasts This isa photomicrographThis is a photomicrograph from the inner aspect of afrom the inner aspect of a bone (a). Newly formed bonebone (a). Newly formed bone is indicated by the tissueis indicated by the tissue underlying the arrow leadingunderlying the arrow leading from (f), and originated by afrom (f), and originated by a layer of osteoblasts (b).layer of osteoblasts (b). Endosteal tissue (c) seperatesEndosteal tissue (c) seperates developing bone from marrowdeveloping bone from marrow tissue (d). The tissue indicatedtissue (d). The tissue indicated by the arrow from (f) is knownby the arrow from (f) is known osteoid, uncalcified boneosteoid, uncalcified bone matrix. (e) seems to representmatrix. (e) seems to represent the interface between thethe interface between the osteoblasts and osteoidosteoblasts and osteoid
- 64. OsteoclastOsteoclast In thisslide, a singleIn this slide, a single osteoclast (c) is working toosteoclast (c) is working to resorb bone that has alreadyresorb bone that has already formed. Note that thisformed. Note that this osteoclast is multinucleated, aosteoclast is multinucleated, a common feature of this cellcommon feature of this cell line. This particular osteoclastline. This particular osteoclast possesses three prominentpossesses three prominent nuclei. The specific area of thenuclei. The specific area of the cell involved in resorption iscell involved in resorption is called the ruffled border (b). Itcalled the ruffled border (b). It is here that the cell secretesis here that the cell secretes enzymes that break down theenzymes that break down the bone. The area marked (a) isbone. The area marked (a) is bone that has not yet beenbone that has not yet been involved in the remodelinginvolved in the remodeling process. Osteoclasts exist inprocess. Osteoclasts exist in special bony pores calledspecial bony pores called Howship's lacunae.Howship's lacunae.
- 65. Cortical Bone CrossSectionCortical Bone Cross Section This section demonstratesThis section demonstrates three key features of corticalthree key features of cortical bone. The familiar Haversianbone. The familiar Haversian canal (a) is the center of thecanal (a) is the center of the osteon. It contains a smallosteon. It contains a small blood vessel supported byblood vessel supported by slender connective tissueslender connective tissue elements. The canal is lined byelements. The canal is lined by flattened osteoblasts andflattened osteoblasts and possibly by osteogenic cells. Apossibly by osteogenic cells. A Volkmann's canal (b) servesVolkmann's canal (b) serves as a connection between twoas a connection between two osteons. Additionally,osteons. Additionally, interstitial lamellae (c) areinterstitial lamellae (c) are seen between the osteons.seen between the osteons. The arrow points to theThe arrow points to the cementing line which formscementing line which forms the boder between twothe boder between two neighboring osteons.neighboring osteons.
- 66. Ground Cortical BoneGroundCortical Bone This transverse section of anThis transverse section of an osteon clearly displays theosteon clearly displays the lamellae of bone surrounding thelamellae of bone surrounding the haversian canal (b). A cementinghaversian canal (b). A cementing line (a) acts to delineate theline (a) acts to delineate the periphery of one osteon fromperiphery of one osteon from others. Note that the canaliculiothers. Note that the canaliculi arising from the peripheralarising from the peripheral lacunae (arrow) do not extendlacunae (arrow) do not extend toward other osteons. Instead,toward other osteons. Instead, they lead toward the haversianthey lead toward the haversian canal. Canaliculi, which appear tocanal. Canaliculi, which appear to anastomose with each other andanastomose with each other and with lacunae, house longwith lacunae, house long osteocytic processes in livingosteocytic processes in living bone. Note the connectionbone. Note the connection between two osteons at the topbetween two osteons at the top left, known as Volkmann's canalleft, known as Volkmann's canal (c).(c).
- 67. Bone LamellaeBone Lamellae This micrographThis micrograph illustrates theillustrates the lamellae of alamellae of a haversian systemhaversian system using polarized light.using polarized light. The alternating lightThe alternating light and dark bands areand dark bands are created by thecreated by the difference in thedifference in the orientation oforientation of collagen fibers incollagen fibers in adjacent lamellae.adjacent lamellae.
- 68. Compact and SpongyBoneCompact and Spongy Bone This is a low powerThis is a low power photomicrograph throughphotomicrograph through the diaphysis (shaft) of athe diaphysis (shaft) of a developing long bone. (a)developing long bone. (a) represents the compactrepresents the compact (cortical) bone, (b)(cortical) bone, (b) represents spongyrepresents spongy (medullary) bone, and(medullary) bone, and (d) marks the(d) marks the periosteum. The dark,periosteum. The dark, basophilic staining tissuebasophilic staining tissue between the spongy bonebetween the spongy bone is bone marrow.is bone marrow.
- 69. Intramembranous BoneIntramembranous Bone In this low powerIn this low power photomicrograph,photomicrograph, developing cortical bonedeveloping cortical bone is seen. (a) representsis seen. (a) represents developing muscle tissue,developing muscle tissue, (b) indictaes the(b) indictaes the periosteum with a layerperiosteum with a layer of basophilic stainingof basophilic staining osteoblasts immediatelyosteoblasts immediately below (c). (d) representsbelow (c). (d) represents a future haversian canal,a future haversian canal, and (e) indicates boneand (e) indicates bone marrow tissue.marrow tissue.