• Dr: mahmoud 3mmar

• mobile: 0106 39 700 30

• F.b: m.3mmar9428@yahoo.com

Address: knowledge village center

Bone1)definition.2)Function.3)Component.4)Types.

definition

Bone: is specialized C.T (cells , fibers , G.S) with calcified inercellular substance.

Functions of bone

1. Skeletal support of body.2. Store of Ca , Po4 .3. Protection of internal organs.4. Manufacturing of blood elements.

component

Tow major component (cellular & matrix)1. Cellular component: 2 cell lineages a) osteogenic cells (4) b) osteoclasts cells2. Matrix component: a) 65% mineral b) 35% matrix (collagen 1,5 & G.s)

1-Osteogenic cells

• Consist of :-

1. Ostoprogenitor cells.2. Osteoblast.3. Bone lining cells.4. Ostocyte.

osteocyte Bone lining cells osteoblast osteoprogenitor

Osteoblast Flatened osteoblast Condensing mesenchyme Mesenchymal tissue origin

Surrounded by bone matrix mineralized or not enclosed in lacuna

Extended on bone surface

On side which will form new bone

1.Haversian canal2.Marow space

3.Periostium4.endosteum

site

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Apoptosis or encased in matrix.ostocyte .

Or remain on bone surface . Bone lining cells.

Osteoblast at vascular area.

Condroblast at avascular area

fate

Through & canaliculi its its maintain contact with adjacent osteocyte&B.LCLarge nucleus & organlles can secrete protien

•Few synthetic organelles

jap junction with ostocyte

.cuboidal or slightly elongated

.rich in protien synsthesis& secretory organelles

Has pale staining elongated nucleus

histology

Maintain bone matrix & can release Ca ion from bone matrix

Control mineral homeostasis & ensure bone vitality & its primary site of ion exchange beween blood and bone

Formation on new bone

Some of them self renewing which insure this cells remain in postnatal bone marrow

function

2- osteoclastic cells

1.origin: a) fusion of blood deriving monocyte b) osteoprogenitor cells in situ

2.site: on bone surface where bone resorption take place

Occupying howships lacunae

3.histology: 1.Large cells often seen in clusters 2. multinucleated (2:100) 3. rich in acid phosphataze enzyme

• Under electron microscope its has unique chrachterestic which is :

1. Ruffiled border.2. Clear zone.3. Vesicular region4. Basal portion

1. ruffiled border:, its osteoclast cell memb. forms finger like projection, adjuacent to bone surface

2.clear zone (seal zone): 1) its the periphery of ruffiled border. 2) its plasma memb. Is opposed closely to bone surface . 3) adjucent cytoplasm to it is are devoided from organelles (clear zone) 4) Its riched in actin & talin

Functions of clear zone:- 1) attach the cells to mineralized surface. 2) isolate an acid environment between cells & bone surface.

NB: lamina limitans: its dense matrix layer between sealing zone & calcified tissue matrix

3.Vesicular region: deep to ruffiled border , its contains vesicle of various shapes.

4.basal portion : its portion away from bone surface consist of many nuclei each of which is surrounded by multiple Golgi complexes ,mitochondria & R.E.R

Bone resorptionIts chemotactic phenomenon since aging

osteocyte may librate some solouble substance during their degrdation this substance attract monocyte to target site that’s will diffrentiate into osteoclast.

This done in sequence of conservative events considered to be as follow:-

1.Attachment: 2.demineralization. (H pump) : cetric , lactic acid chelates bone by H which increase solubility of bone

3.Degrdation of exposed matrix. (acid Po4 , canthepsin b)

4.endocytosis.5.transport.

Matrix component

35% organic65% inorganic

Types of bone

Bone tissue mainly exsist in tow forms

1)Lamellar bone (compact & spongy).

2) Non lamellar bone (woven & bundle).

1.Lamellar bone: this type make up skeleton & flant bones

its subdivided into 2 typesa) Compact bone.b) Cancellous bone (spongy).

A) Compact bone: is dense like ovary . form the main part of shaft of long bones. represent the external covering of cancellous bone of ribs , flat bones.

Lamellar organizationin the shaft of long bone there are three pattern

of lamellar organization of compact bone.

1) Circumferential or basic lamellae (outer & inner).

2) Haversian lamellae.

3) Interstitial lamellae

1)Circumferential lamellae:

a) outer circumferential lamellae: its immediately under periosteum , lamellar deposited at certain number of layers around the circumference of the shaft.

within & between the lamellae numerous osteocyte with their process are filling the corresponding lacuna & canaliculi .

b) Inner circumferential lamellae: its surround the medullary cavity .

Its has similar arrange ment as outer ine but fewer in number.

2)Haversian lamellae :betweenn outer & inner lamellae thre are several groups of concentric lamellae (5:20) each of which surrounds canal has diameter 20:300 micron

Its called haversian canal. Each lamellae has osteocyte concentrically arranged with

their canaliculi radiating toward the central canal.

The inner most canaliculi direct into haversian canal.

Haversian canal contains: B.V , nerves , C.T & lined with osteoprogenitor cells.

Haversian canal run parallel to long axis of shaft of long bone .

Volkmans canals: its branches from haversian canal which connect between haversian canals and ultimately communicate with the surface of bone outside & medullary cavity inside.

its has the same contents of haversian canal.

Haversian system (osteon): its unit structure of compact bone & its consist of canal with surrounding lamellae.

3)Interstitial lamellae: its fragments of lamenated bone tissue tha are packed between osteons .

They represent remnants of older , partialy resorbed , remolded haversian system

2.Spongy bone (cancellous or trabecular bone): this type of bone present in :-

1.Epiphysis of long bone.2.Bony of vertebrate.3.ribs.4.Central part of flat bone.

Histolgy of bone

Its consist of:Inter connected network of bone trabecula with intervening bone marrow space

.bone trabecula consist of : bone lamellae containing osteocyte.

This trabecula surrounded by osteoblast

What is trabecula ?

Its network of bony plates or bars or rods has different orientation which give the spongy bon maximum rigidity

Its also called spicules which means small trabecula

Blood supply of cancellous bone present in:

Intervening marrow spaces, consequently nourishment of oteocyte occurs by diffusion through canaliculi.

Incremental lines of bone (cement lines):-*Its hypo-mineralized lines than bone matrix

Thus its more ductile than matrix , this can increasethe resistance to fatigue failure of bone.

*This lines are (resting & reversal & faint lines).

Faint line Reversal line Resting lineAbrubt change in direction of collagen fibers of each successive lamellae

They indicate postosteoclastic activity occurring on the surface of the bone

undergoing resorption(separate between old & new bone)

( bone turn over).

They demonstrate the incremental pattern of bone formation

(rest of osteoblast).

cause

Silver impregnation H & E H & E Stain

Faint black line Dark blue Dark blue color

In decalcified section

In decalcified and ground section in decalcified and ground section

section

ــــــــــــــــــــ Scalloped lines Undulated lines shape

2. Non lamellar bone its also called:-

1. woven bone . 2. provisional bone . 3. emergency bone .

.its matrix contain more glycosaminoglycan & glycoprotien than lamellated none and thus less mineral contents .

. No. of osteocyte in non lamellar bone is more than that occurs in lamellar bone due to rapid formation of woven bone.

Due to less inorganic contents its more radiolucent in X-ray than lamellar boneAnd this explain why bony healed socket after extraction cant be seen in X-ray.

Bone of emergency is finally resorbed and replaced by lamellar bone.

It will never change directly into lamellar bone.

Periostum: its specialized dense C.T covered all bones of the body except their articular surfaces.

Histologically: its membrane consist of 2 layers, the one being indistinct from other

1. outer layer (vascular layer). 2. inner layer (osteogenic or cambium layer):

.its attached to bone by sharpey‘s fibers while periostium itself act as medium for attachment of muscle , tendons .

.its provide nutritive fonction to underlying bone & has osteogenic proprties in young age.

NB: in oral cavity its called muco-periotium.

endostium

•Its thin single layer of C.T like inner layer of periostium , its lines the medullary cavity of bones.

•Periosteal surface of bone more active in formation of bone than endosteal one.

Oseoid: (osteoid) its layer of newly deposited unmineralized bone matrix that cover bone surface where active new bone formation occurs.

Its 5-10 microne in thickness

Its type 1 collagen fibrilis which slightly parallel to bone surface & proteoglycan and glycoprotien.

Bone development

Bone formation occurs by three mechanisms. 1) endochondral: cartilage is replaced by bone. (UMC diffrenteate into chndroblasts which lay down cartilage which later replaced by bone)

2) intramembranous: occurs directly

3) sutural : bone forming along sutural margins

Bone turnover: its replacement of old bone by new bon.

1. Osteons of fetal bone replaced by larger, more mature & more lamellar bone.

2. Leading edge of resorption is called cutting edge.

3. Behind the cutting cone there is a migration of uni-nucleated cells which differentiate into osteoblast which produce reversal line , thin layer of phosphoprotien which bind old bone to new bone.

4. On the top of reversal line there are formation of new bone .

5. Area where active formation occurs is termed filling cone.

6. Controlling mechanisms of bone resorption may be genatic or hormonal.

7. Bone remodelling accommodates the growth of bone without losing function.

Bone maturation mature bone young immature

boneCoarse woven bone

less undulating less undulating Very undulating Surface periostium

lesser less very cellular cellularity

more organized slightly organized disorganized organization

2ry & 3ry larger osteons

primary small osteons

non osteon

little loose C.T modrate soft tissue contents

haigh vascularity & soft tissue contents

others

Thanks Dr:3mmar