Histogenesis of Bone

8/19/2019 Histogenesis of Bone

http://slidepdf.com/reader/full/histogenesis-of-bone 1/6

Alya Putri Khairani / 130110110220 /

Histogenesis of Bone

HISTOLOGY

Bone is a specialized connective tissue coposed of calci!ed intercellular aterial" the bone matrix, and three

cell types#

• Osteocytes" $hich are found in cavities %lacunae& 'et$een layers %laellae& of 'one atri(

• Osteoblasts" $hich synthesize the organic coponents of the atri(

• Osteoclasts" $hich are ulti)nucleated giant cells involved in the resorption and reodeling of 'one tissue*

Osteoblast

• +esponsi'le for the synthesis of the organic coponents of 'one atri(" consisting of type , collagen !'ers"

Proteoglycans" and several -lycoproteins including .steonectin

• ocated e(clusively at the surfaces of 'one atri(" usually side 'y side in a layer soe$hat rese'ling a

siple epitheliu

• hen they are actively engaged in atri( synthesis" osteo'lasts have a cuboidal to columnar shape and

basophilic cytoplasm* hen their synthesizing activity declines" they fatten and cytoplasmic basophilia is

reduced

• .steo'last activity is stiulated 'y Parathyroid horone %PH&

• atri( coponents are secreted at the cell surface in contact $ith older 'one atri(" producing a layer of ne$

%'ut not yet calci!ed& aterial called Osteoid 'et$een the osteo'last layer and the 'one fored earlier

Osteocytes

• ,ndividual .steo'lasts are gradually surrounded 'y their o$n secretion and 'ecoe Osteocytes enclosed

singly $ithin spaces called Lacunae

• ,n the transition fro osteo'lasts to osteocytes the cells e(tend any long cytoplasic processes" $hich also

'ecoe surrounded 'y calcifying atri(

• An .steocyte and its processes occupy each acuna and the Canaliculi radiating fro it

Osteoclasts

• arge size and ultinucleated condition of .steoclasts is due to their origin

fro the fusion of 'one arro$)derived cells

• ,n areas of 'one undergoing resorption" osteoclasts lie $ithin enzyatically

etched depressions or crypts in the atri( no$n as Resorption Bays

• .steoclast secretes Collagenase and other enzyes and pups protons"foring an acidic environent locally for dissolving Hydro(yapatite andprooting the localized digestion of Collagen

• ,n active osteoclasts" the surface against the 'one atri( is folded into

irregular pro4ections" $hich for Rufed Border. 5urrounding the ru6ed'order is a clear cytoplasic zone rich in actin !laents $hich is the site ofadhesion to the 'one atri(* his circuferential adhesion zone creates aicroenvironent 'et$een the osteoclast and the atri( in $hich 'oneresorption occurs

• Activated 'y PH produce a cytoine called .steoclast 5tiulating 7actor• .steoclasts also have receptors for Calcitonin* hus" activity of these cells is coordinated and 'oth are

essential in 'one reodeling




Bone Matrix

,norganic aterial represents a'out 809 of the dry $eight of 'one atri( %Hydro(yapatite" Bicar'onate" Citrate"

agnesiu" Potassiu" 5odiu&

HISTOG!SIS

Bone priarily develops in t$o types of connective tissue" "esenc#yme and $artila%e" 'ut can also develop in

other connective tissues* ie cartilage" 'one consists of cells and an organic intercellular su'stance)the Bone

"atrix)that coprises collagen !'rils e'edded in an aorphous coponent* 5tudies of the cellular and

olecular events during e'ryonic 'one foration suggest that Osteogenesis and Chondrogenesis are

prograed early in developent and are independent events under the in:uence of vascular events

Osteogenesis

Bone can 'e fored initially 'y either of t$o $ays#

• Intramembranous Ossi&cation

,n $hich .steo'lasts di;erentiate directly fro esenchye and 'egin secreting .steoid

• ndoc#ondral Ossi&cation

,n $hich the atri( of pree(isting hyaline cartilage is eroded and replaced 'y osteo'lasts producing

osteoid

,n 'oth processes" the 'one tissue that appears !rst is priary or $oven* 'rimary bone is a teporary and is

soon replaced 'y the de!nitive secondary laellar 'one* <uring 'one gro$th" areas of priary 'one" areas of

resorption" and areas of secondary 'one all appear side 'y side

%1& ,ntrae'ranous .ssi!cation,ntrae'ranous ossi!cation" 'y $hich ost :at 'ones are produced" is so called 'ecause it taes place $ithin

condensations of e'ryonic esenchyal tissue* ,n the esenchyal condensation layer or =e'rane"= the

starting point for 'one foration is called an ossi&cation center1& he process 'egins $hen groups of esenchyal cells di;erentiate into .steo'lasts2& .steo'lasts produce .steoid atri( and calci!cation follo$s" resulting in the encapsulation of soe

.steo'lasts" $hich then 'ecoe .steocytes3& hese islands of developing 'one for $alls that delineate elongated cavities containing capillaries" 'one

arro$ cells" and undi;erentiated cells>& 5everal such groups arise alost siultaneously at the ossi!cation center" and their fusion 'et$een the

$alls gives the 'one a spongy appearance8& he connective tissue that reains aong the 'one $alls is penetrated 'y gro$ing 'lood vessels and

additional undi;erentiated esenchyal cells" giving rise to the 'one arro$?& he ossi!cation centers of a 'one gro$ radially and !nally fuse together" replacing the original connective

tissue

%2& @ndochondral .ssi!cation aes place $ithin a piece of hyaline cartilage $hose shape rese'les a sall version" or odel" of the 'one to

'e fored* his type of ossi!cation is principally responsi'le for the foration of short and long 'ones1& ,nitially" the !rst 'one tissue appears as a collar surrounding the diaphysis of the cartilage odel2& his Bone $ollar is produced 'y local .steo'last activity $ithin the surrounding Perichondriu




3& he collar no$ ipedes di;usion of o(ygen and nutrients into the underlying cartilage" prooting

degenerative changes there>& he Chondrocytes 'egin to produce Alaline Phosphatase and s$ell up %Hypertrophy&" enlarging their

lacunae8& hese changes 'oth copress the atri( into narro$er ra'eculae and lead to calci!cation in these

structures?& <eath of the Chondrocytes results in a porous three)diensional structure fored 'y the renants of the

calci!ed cartilage atri(& Blood vessels fro the forer Perichondriu no$ the Periosteu penetrate through the 'one collar

previously perforated 'y .steoclasts" 'ringing .steoprogenitor cells to the porous central region& e(t" .steo'lasts adhere to the calci!ed cartilage atri( and produce continuous layers of priary 'one

that surround the Cartilaginous atri( renantD& At this stage" the calci!ed cartilage appears Basophilic" and the priary 'one is @osinophilic* his process

in the diaphysis fors the 'rimary Ossi&cation center10& Secondary ossi&cation centers appear slightly later at the epiphyses of the cartilage odel and

develop in a siilar anner* <uring their e(pansion and reodeling" the priary and secondary

ossi!cation centers produce cavities that are gradually !lled $ith 'one arro$

,n the secondary ossi!cation centers" cartilage reains in t$o regions#

(rticular cartila%e" $hich persists throughout adult life and does not contri'ute to 'one gro$th in length

pip#yseal cartila%e" $hich connects each @piphysis to the <iaphysis

A plate of @piphyseal cartilage is divided into !ve zones" starting fro the @piphyseal side of cartilage#

Chondrogenesis

Cartilage develops fro esenchye and !rst appears in e'ryos during the !fth $ee* ,n areas $here cartilage

is to develop" the esenchye condenses to for $#ondri&cation $enters* he esenchyal cells di;erentiate

1* he Restin% )one consists of hyaline cartilage $ith typical

chondrocytes*

2* ,n the 'roli*erati+e )one, chondrocytes 'egin to divide

rapidly and for coluns of staced cells parallel to the

long a(is of the 'one*

3* he Hypertrop#ic $artila%e )one contains s$ollen

chondrocytes $hose cytoplas has accuulated glycogen*

Hypertrophy copresses the atri( into thin septa

'et$een the chondrocytes*




into $#ondroblasts that secrete collagenous !'rils and the ground su'stance %e(tracellular atri(&*

5u'seEuently" collagenous and/or elastic !'ers are deposited in the intercellular su'stance or atri(* hree types

of cartilage are distinguished according to the type of atri( that is fored#

• Hyaline cartila%e" the ost $idely distri'uted type %e*g*" in 4oints&

• ibrocartila%e %e*g*" in interverte'ral discs&

• lastic cartila%e %e*g*" in auricle of ear&

+eferences

FunEueiraGs Basdic Histoloy 12th @dition

oore he <eveloping Huan

angan edical @'ryology




Periosteum & Endosteum

@(ternal and internal surfaces of 'one are covered 'y layers of 'one)foring cells and vascularized connective

tissue called Periosteu and @ndosteu*

'eriosteum

• Consists of a dense !'rous outer layer of collagen 'undles and !'ro'lasts

• Bundles of periosteal collagen !'ers" called 'er*oratin% -or S#arpeys/ &bers, penetrate the 'one

atri(" 'inding the Periosteu to 'one

• he innerost cellular layer of the periosteu contains esenchyal ste cells called

Osteopro%enitor cells, $ith the potential to divide 'y itosis and di;erentiate into osteo'lasts

• .steoprogenitor cells play a proinent role in 'one gro$th and repair

ndosteum

• A single very thin layer of connective tissue" containing :attened .steoprogenitor cells and .steo'lasts

• Covers the sall spicules or ra'eculae of 'one that pro4ect into these cavities

• Considera'ly thinner than the periosteu




he principal functions of Periosteu and @ndosteu are nutrition of osseous tissue and provision of a continuous

supply of ne$ .steo'lasts for repair or gro$th of 'one

TY'S O BO!S-ross o'servation of 'one in cross section sho$s dense areas generally $ithout cavitiescorresponding to

$ompact Boneand areas $ith nuerous interconnecting cavitiescorresponding to $ancellous %spon%y&

Boneicroscopic e(aination of 'one sho$s t$o types# iature 'rimary bone and ature Secondary bone#

• Priary Bone issue

Priary 'one is the !rst 'one tissue to appear in e'ryonic developent and in fracture repair* ,t is

characterized 'y rando disposition of !ne collagen !'ers and is therefore often called 0o+en Bone. .ther

characteristics of priary 'one tissue are a lo$er ineral content %it is ore easily penetrated 'y ()rays& and a

higher proportion of .steocytes than that in secondary 'ones

• 5econdary Bone issue5econdary 'one tissue is the type usually found in adults* ,t characteristically sho$s ultiple layers of calci!ed

atri( %each 3I J thic& and is often referred to as Lamellar Bone* @ach cople( of concentric 'ony

laellae surrounding a sall canal containing 'lood vessels" nerves" and loose connective tissue is called an

Osteon %forerly no$n as an Ha+ersian system&* acunae $ith .steocytes are found 'et$een the

aellae" interconnected 'y Canaliculi $hich allo$ all cells to 'e in contact $ith the source of nutrients and

o(ygen in the osteonic canal* he outer 'oundary of each .steon is a ore collagen)rich layer called the

$ement Line

Histogenesis of Bone

Documents

Transcript of Histogenesis of Bone