Bones Osama Yousef & Neveen Nazzal 05/11/2010
Bones 9th Lecture
Introducaiton..................................................................................2 Osteoblasts........................ Osteoblasts.............................................. ............................................ ............................................ ......................................3 ................3
Mineralization in bone matrix......................... matrix......................................... ................................ ......................4 ......4 Osteocytes................................................................................................................5 Osteoclasts.......... Osteoclasts............................. ...................................... ...................................... ...................................... ...................................... .............................6 ..........6 Periosteum and endosteum Periosteum and endosteum...................................7 Types T ypes of bones....................... bones.......................................... ...................................... ...................................... ...................................... ............................8 .........8 How laamellaes laamellaes are organized........... organized.............................. ..................................... ..................................... .................................9 ..............9 Bone Remodeling........ Remodeling........................... ..................................... ..................................... ...................................... .....................................1 ..................10 0 Bone growth and repair................. repair.................................... ...................................... ...................................... ...................................12 ................12 Final word.................... word....................................... ...................................... ..................................... ..................................... ...................................... ...................13 13
Introducaiton
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one is a specialized orm o connective tissues that has a calcied intracellular matrix. It supports eshy organs and protects Vital Vital organs (such as those in the Cranial and thoracic cavities). Also bones serve as a reservoir o Calcium, phosphate, and other ions.Tey also orm a system o livers that generate orces during skeletal muscle contraction thereore bone has both metabolic and mechanical unctions to the skeleton.Bone is composed o : (a)Bone Matrix (intercellular material ) and (b) the three cells types : Osteocytes, Osteoblasts and Osteoclasts. Matrix : “Is the intercellular Material that is Impregnated with Inorganic salt and its composed o Organic and Inorganic Material “. Inorganic material consists mainly o “Hydroxyapitite “Hydroxyapitite Crystals” Crystals” whose cells is hydrated and acilitate the ion exchange between the crystal crystal cell and the intercellular uid (Body Fluid). Other Ions are available in the inorganic matrix like: Bicarbonate Citrate, Citrate, Magnesium,potassium,sodium and in addition to noncrystalline Calcium phosphate (CaPO ). Organic Material consists o “ype “ype one (l) Collagen fber , proteoglycan roteoglycan aggre gates and Multiadhesive glycoprotein(occur in the connective and cartilage tissue). “Te associations o minerals with collagen fbers give the hardness and resistance o a bone, so removing the organic material will leave the bone ragile and can be easily broken. “
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Mineralization in bone matrix
Osteoblasts Tere are some examples about the bone we should know about they are : Fibro-nekton: Example o connective tissue, Condo-nekton: Example o Cartilage tissue and Osseo-nekton: Example o Bone Matrix.Now lets talk more about the cells types o the bones , we will start wth the rst type which is the Osteoblasts cells.Tey are Cells that are arranged in one layer (somewhat resembling an epithelium cells ). Tey are ound in cavities (lacunae (lacunae)) between layers (lamellae (lamellae)) o bone matrix. Tey Synthesize and Secrete the organic matrix o bone which then hardens by calcication. Tey synthesis type I collagen bers , proteoglycans and several glycoproteins which all o them is needed in the process o “Bone Mineralization” (discussed shortly) . Teir activity is stimulated by parathyroid Hormone (PH) . Te shape o theosteoblasts depends on their synthetic Activity (PH) , when they have high synthetic activity the shape will be “ Cuboidal to Columnar “ Columnar “ and basophilic cytoplasm. cytoplasm. I the synthetic activity is low then the shape will be “Flattened “Flattened “and “and there will be a decreases in plasmatic basophilia. basophilia. Osteoblasts are developed (derived) rom mesenchymal cells. cells. Look at gure 2 here we have Osteoblasts (OB) and Osteocytes(O). OB are derived rom the mesenchymal cells nearby and they appear as a simple row o cells . In gure 3 we can see the relatonship o Osteoblasts , the Osteoid and Osteocyte.Osteoid is : “Newly ormed, ormed, less staind bone matrix that is not yet calcifed”.
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From their ends adjacent to the matrix , osteoblasts secrete : 1) ype l collagen. 2) Several glycoprotens 3) Proteoglycans 4) Osteocalcin and some certain glycoprotens, they do the ellowing things : Tey bind Ca with high anity thus >> increasing the local concentration o Calcium. 5) ) Small membrane-enclosed matrix vessels with alkaline phosphate and other enzymes, they do the ellowing things : Tese enzymes hydroliaze hydroliaze PO thus having high local concentration o PO. When there is a high level o Ca (osteocalcin eect) + high level o PO (small matrix vessels eect) the ollowing series happens: -High conc. Ca & PO >>ormation o CaPO4 crystals on the matrix vessels >> these crystals undergo urther growing + they orm small growing masses o Hydroxyaptie >> this Hydroxyaptie surrounds the collagen bers and all other macromolecules >> as soon as the calcication o the matrix is completed the small masses merge as a conict solid bony matrix .
gure 2 showng the location o Osteoblasts
gure 3 showing o Osteoblasts , the Osteoid and Osteocyte
gure 4 showing the mineralzation process n the bone matrix
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Osteoclasts
Osteocytes The osteocytes are the Osteboblasts that gradually become surrounded by their own secretion and become Osteocytes and they become enclosed singly within spaces called Lacunae. In the process of transforming the osteoblasts into osteocytes the cells extend many long cytoplasmic process so an osteocyte and its cytoplasmic process occupy two things, Osteocytes occupy Lacuna and Cytoplasmic process occupy canaliculi. canaliculi . ** Note : Canaliculi & Lacuna have the same name of space in Chondrocytes Osteocy Osteocytes tes with Osteoid (classied osteoid).
Osteoclasts are very large (giant multinucleated).They are multi- nucleated and very large because they are derived from monocytes which are from the bone marrow.Look at gure 6 (a) and (b) this conconcavity at the surface of the bone (rufed ( rufed border ) it’s modify the surface of osteoosteoclasts.You can see can see an area of clear circumferential adhesion zone this is the circumferential zone from its name you can see that it is gure 6 showng Osteoclasts and thier cavities for the adherence for the osteoclasts,to the bone surface which is rich in actin lament, you can also see an area of clear zone rich of actin laments Which is the site of adhesion to the bone matrix “cir“ circumferential adhesion zone “as the name indicate it source for the adhesion for osteoclasts to the bone surface
Look at gure 5 (a) This TEM section shows the osteocyte with its ctytoplasmic processes surrounded the by the matrix you can see that this cell is inactive by looking to it cytoplasm .There .There is no rough endoplasmic reticulum (RER) neither is there well-developedm Golgi apparatus. (b) this is dried section; all organic ma trix is gone. Lacunae and Canaliculi ap pears dark and show the communication between these structures where nutrients derived from blood vessels passed from cell to cell in this living bone
Gap Junction (Nexus): cytoplasmatic Processes o adjacent cells make contact via these gaps. Molecules also pass rom cell to cell through it Te communication between osteocytes occurs by gap junction (cytoplasmatic process o the canaliculi communicate)
gure 6 showng Osteoclasts and thier cavities
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gure 5 showing the gap junctions
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Periosteum and endosteum Similar to the pericardium there is something called “ periosteum (( peri : means around or supporting the osteum bone )) remember that most these connective tissue has “ Osteoprogenitor Osteoprogenitor cell “ that means that the cells have high potential to synthesize and orm bone. Te Osteoprogenitor cells is dierentiate into osteoblasts which synthesize the bony matrix which then undergoes calcication orming the bone .” Periosteum and Endosteum are both connective tissue , they have blood vessels to provide provide the bone with nutrition and have the prominent prominent role in bone growth and repair because they contain the osteoprogenitor cell.” 1) Te periosteum is composed o 2 layers : (a) Te outer layer >>> layer >>> consists o dense brous rich in collagen bers bundles and broblasts .Bundels .Bundels o periosteal collagen bers called Peroratng or (sharpe). (sharpe). (b)Te (b)Te Inner layer (Innermost layer ) >>> contains mesenchymal stem cells called osteoprogenitor cells , they play an important role n bone growth and repair. 2) Endosteum(inside): A single thin layer o connective tissue that surround long bone that cover the internal & external suraces o bone ( lines the internal narrow cavity ) they contain the osteoprogenitor cells and the osteoblasts. Figure 7 shows the Periosteum and en-
Types Types of bones Look at gure 8 By looking at the bone microscopy the gross observation shows dense area without cavities it is called “Com“Com pact bone “ the other type you can can see that it contains numerous cavity and it is called Cancellous or or (spongy ) bone. In living tissue the compact bone is covered externally with periosteum and all surace o cancellous bone with endosteum .Now lets talk about the types o bones we have.Tere is primary bone and Secondary bone. primary bone >>> Newly ormed , immature bone , rich in osteocy tes.It is characterized by 1) random disposition o ne collagen bers and t hereore it is called “Woven “Woven bone” 2) ) lower mineral content 3) higher proportion o octeocytes than that in secondary bones 4) due to not h aving the lamellae ( will be discussed shortly ) thus we call it the moving bone , there is just random disposition o ne collagen bers without being arranged in lamellae.5) it is temporary, it is replaced by secondary bone tissue , (only ew placed like near the sutures , tooth sockets and in the insertions o some tendons ).
gure 7 showing Periosteum and endosteum
dosteum P = Periosteum and E= Endosteum.
gure 8 showing the compact and cancellous bone
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gure 9 shownig the primary bone
Look at gure 9 Tis gure shows the primary ( Woven ) bone undergoes a repair process ,they are newly ormed , immature bones , rich in osteocytes and with randomly arranged bundles o calcied collagen
Secondary bone Tis type is usually ound in adults. And it is the permanent bone type , it can be characterized as : 1) having multiple layers o calcied matrix reerred to as lamellar bone. bone. Tese laamellaes are quite organized they can be seen either parallel to each other or concentrically around a vascular canal.2) each complex o concentric bony lamellae surrounding a small canal contains blood vessels , nerves and loose connective tissue is called an Osteon; or haversian system.By looking at gure 10 In this micrograph you can see the secondary bone shows matrix organized as lamellae. lamellae. Each complex o concentric-lamellae surrounding a small canal containing blood vessels, nerves and loose connective tissue is called Osteon ( Harversian system ) Remember that secondary bone is permanent Mature and major bone. Looking at gure 11 we can see Secondary bone shows many osteon(O) and the outer boundary o each osteon is called cement line ( more collagen –rich layer.
Bone Remodeling
gure 10 showing the secondary bone
How laamellaes are organized
In compact bone ( beside orming osteon ) , the lamellae exhibit a typical organization o multiple External circumerential lamellae ( located beneath the periosteum ) and the Inner circum erential lamellae ( located around the marrow cavity ) Among the osteons between the two circumerential systems and irregularly shaped groups o parallel lamellae called Interstitial Lamellae Te central canals communicate with the marrow cavity and the peiosteum and with one another through transverse or oblique “Peroratng canals” also known as Volkmann canals.
Involves a combination o bone removal and synthesis. In secondary bone remodeling resorption part o old Osteons and produce new ones in tunnel-like cavities having the approximate diameter o new Osteons you have population o Osteoclasts that cavity lining it and producing Osteoid , afer that the Osteoid goes calcication and mineralization orming the bone.Remember that bone remodeling involve bone resorption by osteoclasts and orming osteoid . Bone can be ormed by two ways : 1) Intramembranous ossifcation >> rom inside the membranes that the bone ormed 2)Endochondral ossifcation >> Te matrix o pre-existing hyaline hyaline cartilage is eroded and replaced by osteoblasts producing osteoid. In both process ,the bone tissue that appears rst is primary or woven. Primary bone is temporary and is soon replaced by the denitive secondary lamellar bone During bone growth , areas o primary bone , areas o resorption , areas o secondary bone all appear side by side.Most at bone ormed by Intramembranous by Intramembranous ossifcation but in the short and long ormed by Endochondr by Endochondral al ossifcation .
gure 11 showing osteons
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10 gure 12 shownig Intrambranous ossication
Intrambranous ossifcation ossifcation (fgure 12) : Tis gure shows the intramembranous ossifcation, ossifcation, so rst a cluster o mesenchymal cells dierentiate into osteoclasts remember that osteoclasts secrete the osteoid .You .You can notice that groups o mesenchymals ound in a membrane ( sheet ) o the embryonic tissue producing osteoid . Oseoblasts have cytoplasmatic process trapped in bone which is called osteocytes instead o osteoblasts you can see only the primary bone .Tis woven bone is surrounded by developing periosteum . Continuous remodeling produces two layer o compact lamellar bone with cancellous bone in between which is characteristic o the at bone .
Endochondral (fgure 13) : In this gure you can notice the hyaline cartilage that will give rise to orm the bone , afer that you have the perichondrium that surrounded the hyaline cartilage and become the periosteum >>producing the color o the bone ,the collar impedes diusion o oxygen and nutrient into the underlining cartilage promoting the degenerative change , afer that the osteoblasts with the blood vessels degenerate this area where the color o bone is ormed and ollowed by invasion.Te osteoblasts secrete osteoid m, afer that there will be mineralization and calcication . Te area where the ossication start the bone orming in diaphysis ( shif o bone ) is called the primary ossifcation center . Later in development another ossication center development in the epiphyses o the cartilage model is called t he secondary ossifcation centers Between the primary and the secondary you have the epi physeal plate ( growth plate ) that provides the elongation o bone Tey stay at there capacity ( merge ) and there will be
remodeling to bone to be longer and at the end o growth both the ossication center euse & the epiphyseal plate ( growth plate ) disappear . Note : Bone collar is produced by local osteoblasts activity within the surrounding perichondrium .
Bone growth and repair By looking at ugre 14 we can see photomicroscope o the epiphyseal plate with its ve zone.1) Resting zone : consists o hyaline cartilage.2) Prolierative zone : increase the number o cells.3) Hypertrophic cartilage zone : increase number o sites o the cell.4) calcifed cartilage zone : happens the calcication.5) Ossifcation zone. you can see rom fgure these zones frst the resting the second zone is Prolierative(increase num o cells) then the hypertrophic (blue (blue color area ) then the calcifed and the ossifcation zone . Bone repair Bone have high potential cavity or repair regeneration because o the presence o the osteoprogenitor stem cells and extensive o blood supply both are important important or bone growth growth . Te rate o bone remodeling ( bone turnover ) is very active and aster in young children children than in adult . Bone remodeling in adult is not always related to bone Growth.
gure 13 showing Endochondral ossication
gure 14 showing epiphyseal growth plate.
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“Bone is very plastic and capacity or changes in the structure due to remodeling and according to various stresse. Synthesize o new bone . Example : can seen in change o the teeth position o the orthodontic treatment .” THE END
- Neveen Nazzal : “Finally …. 5l9na W Salame la kol al Do3a Bs 7aba a7ke akm $a3’la snem ... Ur Ur the best(B) Ra3’s … I trust U Do7a w Nada … Tnx 4 supporting me in every Ting ,,, I’ll geel U “ -Osama Youse : “I made the design o this lecture dirent rom the others , here the design is more like the textbook we read enshallah you like it and enshllah I’ll make more o the lectures in the near uture.Mohamed Al-Esayi , Majd Hdmi , Amr Alsade , Mohamed Haroon , Ali-Alqdsi and Ahamad Kesate thank you all.And ocourse thank you Neveen or your writnig/editing this lecture. Kepada rakan-rakan Malaysiaku, Semoga Berjaya di dalam peperiksaan ini. erutama kepada Ulya, Najib, Furqon, Azzam dan Anur
