alveolar bone -vandy
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Introduction
Classification
Composition
Histology Bone formation
Bone turnover
Bone remodeling
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Bones are calcified connective tissue forming the
major portion of the skeleton of most vertebrates
more calcium than any other organ
consists of a dense organic matrix and an
inorganic, mineral component
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Functions of the bone in brief;
toughness and elasticity
shape and support
site of attachment for tendons and
muscles
Protects vital organs of the body
Serve as a storage site for minerals provides medium for development and
storage of blood cells
marrow
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Bones may be classified according;
Shape.
Mode of development.
Histologic appearance.
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Classification based on shape:
Long bones.Flat bones.
Irregular bones.
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They are long and slender.
Longer than wider.
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Cube shaped of nearly equal length and width.
Consists of spongy bone covered by thin layer ofcompact bone.
Examples;
bones of wrist and ankle.
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Thin, flat ,curved with no marrow cavity.
spongy bone is present between upper and lower layer
of compact bone.
Examples; sternum,ribs,clavicle
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Have complex shapes, notched or with ridges.
Made of spongy bone covered with layer of compactbone.
Examples;
vertebrae,mandible, sphenoid,pelvic bones.
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Endochondral bones
Bones of trunk and extremities
Intramembranous bones Cranial and facial flat bones of the skull, mandible and clavicles.
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Histologically;
Two types;
Mature bone
Immature bone
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Mature bone
Two types
compact (cortical) bone
cancellous(spongy) bone
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Woven/immature bone.
First formed bone with irregularly oriented collagen fibers of varying
diameter.
Present in
alveolar bone
healing of fractures.
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67% 33%
inorganic organic
hydroxyapatite 28% 5%
collagenOsteocalcin
Sialoprotein
Phophoprotein
Osteonectin
Bone specific protein
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The mineral component; hydroxyapatite
thin plates or leaf like structures
packed closely with long axis nearly parallel to collagenfibril axis
The narrow gaps between the crystals contain water
and organic macromolecules. Ions present;
Carbonate,calcium phosphate,hydroxyl.
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5% of the total organic content of bone matrix.
Endogenous proteins produced by the bone cells.
Albumin is derived from the blood and become
incorporated into the bone matrix duringosteosynthesis.
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Osteocalcin; noncollagenous protein 15% of the noncollagenous bone protein. Also known as bone Gla protein
Aminoacid gamma carboxy glutamic acid.
Regulation by vitamin D and parathyroid hormone.
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Osteopontin and bone sialoprotein ;
heavily glycosylated and phosphorylated
high levels of acidic aminoacids
Aspartate Glutamic acid
Potent inhibitor of
hydroxy apatite
crystal growth.
Plays role in the
intiation of mineral
crystal formation.Transcription is
upregulated by
vitamin D3
suppressed by
vitamin D3
osteopontin sialoprotein
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Osteonectin
25% of noncollagenous proteins
bound to hydroxyapatite crystal
regulation of cell adhesion
proliferation and modulation of cytokine activity
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Proteoglycans
A large chondroitin sulphate proteoglycans
Non mineralized bone matrix
Small proteoglycans, biglycan and decorin(
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Lysyl oxidase(collagen cross linking) and tyrosine rich
acidic matrix protein(TRAMP) Demineralised bone and bone matrix
TRAMP( dermatopontin) binds decorin and TGF-beta
Regulate the cellular response to TGF beta
Others
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Dense outer sheet ofcompact bone and a central
medullary cavity
Cavity is filled with red or yellow bone marrow
interrupted, particularly at the ends of long bones, bya network of bone trabeculae ie.trabecular, cancellous,
or spongy bone
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Circumferential lamellae;At the periosteal and endosteal surfaces, the lamellae inparallel layers surrounding the bony surface
Concentric lamellae;Deep to the circumferential lamellae, the lamellae are arranged
in concentric layers around a central vascular canal
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Interstitial lamellae: are interspersed between
adjacent concentric lamellae and fill the spaces
between them
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Red
marrow
young
bone
yellowmarrow
oldbone
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osteoblasts
osteocytes
osteoclast
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mononucleated cells
synthesis and secretion of macromolecular
organic constituents of bone matrix
osteoprogenitor cells of mesenchymal origin
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undifferentiated pluripotent stromal stem cells
differentiate into inducible osteoprogenitor cells(IOPCS)
IOPCs
Determined osteoprogenitor cells(DOPCS)
osteoblast
Osteoblasts
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Formation of new bone via synthesis of various proteins
and polysaccharides
Regulation of bone remoldeling and mineral metabolism
In the mineralization of osteoid
Osteoblasts
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Bone resorbing factors
parathyroid hormone,
vitamin D3,interleukin1
tumor necrosis factor
Receptor for these bone resorbing agents
Recognize the resorptive signal and transmit it to the
osteoclast
Osteoblasts
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The overall integrity of bone is controlled by;
Hormones
Protein secreted by hematopoietic bone marrow
cells
Bone cells
Osteoblasts
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In response of hypocalcemia;
hormone activates the mechanism for the release ofcalcium from the bone
PTH does so;
indirect effect mediated by PTH receptors on bonestromal cells including osteoblast
Osteoblasts
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Stimulates bone resorption
Essential for normal bone growth and mineralisation
Promotes calcium absorption from the intestine
stimulates synthesis of osteocalcin and osteopontin by
osteoblast
suppresses collagen production
Osteoblasts
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Parathormone and vitamin D3 enhance;
bone resorption at high concentration(pharmacological) bone formation at low(physiological)
Osteoblasts
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Required for attaining normal bone mass;
Mediated by the local production of IGF-1
Binds to membrane growth hormone receptors on
activated osteoblast
Osteoblasts
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It targets osteoblast directly
Stimulates bone matrix formation
Mineralisation Indirectly affects bone formation through
stimulation of IGF-1
Osteoblasts
Osteoblasts
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Formation of new bone including;
Migration
Aggregation
Proliferation of mesenchymal type cells
Differentiation into osteogenic cells
Osteoblasts
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Osteoblasts after, completing their function got
entrapped in bone matrix and become osteocytes or
remain on the surface as the lining cells
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Osteoblasts form the bone matrix, they got entrapped
within the matrix they secrete and are called as
osteocytes
The number of osteoblasts that become osteocytes,
depend on the rapidity of bone formation
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Osteocytic lacunae;
within the bone matrix, the osteocyte reduce in
size creating a space around it
ovoid or flattened
Osteocytes
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Narrow extensions of these lacunae forms channels
called canaliculi
Osteocytic processes are present within these
canaliculi;
contain bundles of microfilaments and smooth
endoplasmic reticulum.
Osteocytes
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At the distal end, these processes contact
the processes of adjacent
cells(osteocytes)
contact with osteoblasts and bone liningcells at the surface
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The word osteoblast is derived from the Greek words
for bone and broken
Removes bone tissue by removing the mineralized
matrix of bone
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Osteoclasts lie in resorption bays called Howships
lacunae.
large cell approximately 40-100m in diameter with 15to 20 closely packed nuclei.
multinucleated osteoclast resorb more bone than with
few nuclei.
Osteoclasts
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The cytoplasm also microtubles which transport vesicles
between golgi stacks and ruffled membrane
Cathepsin containing vesicles and vacuoles are present
close to the ruffled border indicating resorptive activity
of these cells
Osteoclasts
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Haemopoietic cells of monocyte macrophage
lineage
Proliferate and differentiate into osteoclasts
through a mechanism involving cell-cell
interaction with osteoclast stromal cells
Osteoclasts
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The formation requires the presence of RANK ligand
and M-CSF
Neighboring stromal cells and osteoclast precursor
RANK Ligand and M-CSF
Osteoclasts
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RANKL;
Differentiation into mature osteoclast
osteoclast activity
RANK is expressed by osteoclast precursors, a
membrane bound TNF receptor that recognizes RANKLthrough direct cell to cell interaction with osteoblast
or stromal cells
Osteoclasts
Osteoclasts
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The soluble TNF receptor family member OPG is a
natural RANKL antagonist ;
inhibit osteoclast formation and bone resorption.
Estrogen suppresses the ;
production of bone resorbing cytokines including IL-1
and IL-6.
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Calcitonin inhibits;
proliferation differentiation of osteoclast precursors
reduces the dimension of ruffled border and
dissociation into monocytic cells
Osteoclasts
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Three mechanisms
Endochondralbone growth
Intramembranousbone growth
Sutural bonegrowth
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Take place when the cartilage is replaced by bone.
Site;
At the ends of long bones
Vertebrae
Ribs
Head of the mandible
Base of the skull
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Mesenchymal cells
condenses and differentiate into chonbroblast
cartilage matrix(hyaline cartilage model)
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Hyaline cartilage model is surrounded by
perichondrium
Perichondrium;two layers Inner chondrogenic layer
outer fibrous layer
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The growth of cartilage model;
Intersititial growth
Appositional growth
Intersititial growth
Increase in the length
repeated division of chondrocytes
production of additional matrix by the daughter
cells.
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Appositional growth
Widening of the model
addition of matrix to its periphery by new
chondroblasts
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Zone of proliferation
Zone of hypertrophyand maturation
Zone of provisionaland mineralization
As the differentiation of cells
move towards metaphysis.
Cells organize into longitudinal sections
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Zones of proliferation;
The cells are small and flat
Constitute a source of new cells
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The chondrocytes hypertrophy
Secrete Type II collagen
As hypertrophy proceeds, proteoglycans are secreted Partial breakdown of proteoglycans, creating a matrix
environment receptive for mineral deposition
Zone of hyper t rophy and
maturat ion
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Formation of matrix vesicles
These membrane bound vesicles bud off from the cell
and form independent units in the longitudinal septa of
the cartilage
Zone of prov is ional m ineral isat ion
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In this bone develops directly within the soft connective
tissue rather than on a cartilaginous model
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It involves following steps;
Formation of bone matrix within the fibrous
membrane
The mesenchymal cells proliferate and condense
As vascularitry increases at the sites of condensed
mesenchyme, osteoblasts differentiate and begin to
produce bone matrix de nova
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At the multiple sites within each bone of the cranial
vault
MaxillaBody of the mandible
Midshaft of long bones
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The bone spicules gradually lengthen into longer
structures called as trabeculae
The trabeculae extend in a radial pattern and these
enclose blood vessels
Woven bone;early membrane bone
Periosteum ;external to woven bone,
condensation of vascular mesenchyme.
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In richly vascular areas, these osteogenic cells give
rise to osteoblasts that form the bone matrix
In areas, with no capillary blood supply, they form
the chondroblasts which lay down cartilage
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Osteoblasts and osteogenic cells
Proliferate in a highly vascularised environment
osteoblasts
Deposit new layers of bone matrix on preexisting bone
surface.
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Osteogenic cells are always in superficial position
repeating the process again and again
This is appositional growth which result in build of
bone tissue one layer at a time
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The number of narrow canals are formed linedby osteogenic cells
These canals enclose blood vessels(in soft tissue
spaces of cancellous network)
The consecutive lamellae of bone become added
to the bony walls of spaces in cancellous bone
which is called osteon or haversian system
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Permit skull and face to accommodate
growing organs such as eyes and brain
Same osteogenic potential as periosteum Skull bones forced apart by the growing
brain-bone forms at the sutural margins, with
waves of new bone cells differentiating from
the cambium
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Young immature bone is relatively thin, with few osteons.
Its periosteal surface is undulating and forms bone rapidly
Its endosteal surface is primarily for resorption.
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The immature bone grows.
Its periosteal surface is not as undulating and
produce large number of secondary osteons.
The primary osteons are resorbed.
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The bone nearly matures.it is thicker still, its periostealsurface is less undulating and teritary osteons replace
secondary osteons.Fragments of both primary
and secondary osteons forms interstitial lamellae
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It is the replacement of old bone by new
bone
Cutting cone;
The leading edge of resorption
it is characterized in cross section by scalloped
array of Howships lacunae,each housing anosteoclast
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Remodeling is the major pathway of bony changes in
shape, resistance to forces, repair of wounds, and
calcium and phosphate homeostasis in the body.
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Osteoclasts have resorbed organic matrix along
with hydroxyapatite
The breakdown of collagen from the organicmatrix releases various osteogenic substrates -
stimulates the differentiation of osteoblasts,
which - deposit bone
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Orbans: Oral Histology and Embryology 2000, 12th
edition.
Ten Cates Oral Histology, Development, structure and
function- 2005, 5th edition.