Bone is a composite material formed mostly of calcium phosphate. There are two types of bone tissue: compact bone and spongy bone. Cortical bone accounts for 80% of the total bone mass in the adult skeleton. There are two processes of bone formation: intramembranous ossification which forms flat bones of the skull, and endochondral ossification which forms most other bones through a cartilage model. Bone is constantly remodeled through the actions of osteoblasts which build bone and osteoclasts which break it down.

1. Growth andGrowth and
Development of BoneDevelopment of Bone

2. IntroductionIntroduction
 Bone is a relatively hard and lightweightBone is a relatively hard and lightweight
composite material, formed mostly ofcomposite material, formed mostly of
calcium phosphatecalcium phosphate
 Bone can be eitherBone can be either compactcompact oror
cancellouscancellous (spongy).(spongy). CorticalCortical (outer(outer
layer) bone is compactlayer) bone is compact
 Cortical bone accounts for 80% of the totalCortical bone accounts for 80% of the total
bone mass of the adult skeletonbone mass of the adult skeleton

3. Types Of BonesTypes Of Bones
 Long BonesLong Bones
 Short BonesShort Bones
 Flat BonesFlat Bones
 Irregular BonesIrregular Bones
 Pneumatic BonesPneumatic Bones
 Sessamoid BonesSessamoid Bones

4. Bone cellsBone cells
 OsteoblastsOsteoblasts are typically viewed as bone forming cells.are typically viewed as bone forming cells.
 OsteocytesOsteocytes originate from osteoblasts which haveoriginate from osteoblasts which have
migrated into and become trapped and surrounded bymigrated into and become trapped and surrounded by
bone matrix which they themselves produce.bone matrix which they themselves produce.
 OsteoclastsOsteoclasts are the cells responsible for boneare the cells responsible for bone
resorption. Osteoclasts are large, multinucleated cellsresorption. Osteoclasts are large, multinucleated cells
located on bone surfaceslocated on bone surfaces
 Lining CellsLining Cells come from osteoblasts which have becomecome from osteoblasts which have become
flattenedflattened.. Bone lining cells have flat organelles so theyBone lining cells have flat organelles so they
can easily cover the bone without interfering with othercan easily cover the bone without interfering with other
cells functionscells functions..

5. Developmental ClassificationDevelopmental Classification
 Membranous BonesMembranous Bones ossify in membraneossify in membrane
(intramembramous or mesenchymal Ossification). Eg.(intramembramous or mesenchymal Ossification). Eg.
Bones of Vault of Skull & Facial BonesBones of Vault of Skull & Facial Bones
 Cartilagenous BonesCartilagenous Bones ossify in cartilageossify in cartilage
(intracartelagenous or endochondral Ossification). Eg.(intracartelagenous or endochondral Ossification). Eg.
Bones of Limbs, Vertebral Column & Thoracic CageBones of Limbs, Vertebral Column & Thoracic Cage
 Membrano-Cartilagenous BonesMembrano-Cartilagenous Bones ossify partly inossify partly in
membrane and partly in cartilage. Eg. Clavicle,membrane and partly in cartilage. Eg. Clavicle,
Mandible, Occipital, Temporal, SphenoidMandible, Occipital, Temporal, Sphenoid

6. Intramembranous OssificationIntramembranous Ossification
 Intramembranous ossificationIntramembranous ossification is one ofis one of
the two essential processesthe two essential processes
duringduring fetalfetal development of thedevelopment of the skeletalskeletal
systemsystem by which rudimentaryby which rudimentary bonebone
tissuetissue is created.is created.

7. Stages of IntramembranousStages of Intramembranous
OssificationOssification

8. Stages of IntramembranousStages of Intramembranous
OssificationOssification

9. Stages of IntramembranousStages of Intramembranous
OssificationOssification

10. Stages of IntramembranousStages of Intramembranous
OssificationOssification

11. Endochondral OssificationEndochondral Ossification
 Begins in the second month ofBegins in the second month of
developmentdevelopment
 Uses hyaline cartilage “bones” as modelsUses hyaline cartilage “bones” as models
for bone constructionfor bone construction
 Requires breakdown of hyaline cartilageRequires breakdown of hyaline cartilage
prior to ossificationprior to ossification

12. Formation
of bone
collar
around
hyaline
cartilage
model.
1
2
3
4
Cavitation
of the
hyaline
cartilage
within the
cartilage
model.
Invasion of
internal cavities
by the
periosteal bud
and spongy
bone formation.
5 Ossification of the
epiphyses; when
completed, hyaline
cartilage remains
only in the
epiphyseal plates
and articular
cartilages
Formation of the
medullary cavity as
ossification continues;
appearance of
secondary ossification
centers in the
epiphyses in
preparation for stage 5.
Hyaline
cartilage
Primary
ossification
center
Bone
collar
Deteriorating
cartilage matrix
Spongy
bone
formation
Blood
vessel of
periostea
l bud
Secondary
ossification
center
Epiphyseal
blood vessel
Medullary
cavity
Epiphyseal
plate
cartilage
Spongy
bone
Articular
cartilage
Stages of Endochondral OssificationStages of Endochondral Ossification

13. Bone ResorptionBone Resorption
 While osteoblasts and osteocytes are addingWhile osteoblasts and osteocytes are adding
new bone to the outer surface, osteoclasts arenew bone to the outer surface, osteoclasts are
removing bone at the inner surface andremoving bone at the inner surface and
enlarging the marrow cavityenlarging the marrow cavity
 Osteoclasts make contact with the bone throughOsteoclasts make contact with the bone through
a region referred to as ruffled border anda region referred to as ruffled border and
subsequently have the ability to degrade bothsubsequently have the ability to degrade both
inorganic and organic matrices of the boneinorganic and organic matrices of the bone

14. Types of MarrowTypes of Marrow
 Red marrow – chief blood cell formingRed marrow – chief blood cell forming
organ of the adult and is found in spongyorgan of the adult and is found in spongy
bone of the epiphysis of long bones andbone of the epiphysis of long bones and
main bodies of ribs, sternum andmain bodies of ribs, sternum and
vertebraevertebrae
 Yellow marrow – composed mainly ofYellow marrow – composed mainly of
adipose tissue and found in the medullaryadipose tissue and found in the medullary
cavity of bonescavity of bones

15. Bone RemodelingBone Remodeling
 Osteoblasts form osteons (basic functional unit ofOsteoblasts form osteons (basic functional unit of
compact bone) by osteogenesis whereas osteoclastscompact bone) by osteogenesis whereas osteoclasts
destroy osteons by resorption.destroy osteons by resorption.
 The balance between these two yields net boneThe balance between these two yields net bone
depositiondeposition
 As animals age, bone resorption may exceed formationAs animals age, bone resorption may exceed formation
and bone mass decreasesand bone mass decreases
 Bones grow through a process of Appositional Growth-Bones grow through a process of Appositional Growth-
Formation of new bone on the surface of older bone orFormation of new bone on the surface of older bone or
cartilagecartilage

16. Long Bone Growth and RemodelingLong Bone Growth and Remodeling

17. Osteoblasts beneath
the periosteum
secrete bone matrix,
forming ridges that
follow the course of
periosteal blood
vessels.
1 2 3 4As the bony ridges
enlarge and meet,
the groove
containing the
blood vessel
becomes a tunnel.
The periosteum
lining the tunnel is
transformed into an
endosteum and the
osteoblasts just
deep to the tunnel
endosteum secrete
bone matrix,
narrowing the canal.
As the osteoblasts
beneath the endosteum
form new lamellae, a
new osteon is created.
Meanwhile new
circumferential lamellae
are elaborated beneath
the periosteum and the
process is repeated,
continuing to enlarge
bone diameter.
Artery Periosteum Penetrating canal
Central canal of osteon
Periosteal ridge
Appositional Growth of BoneAppositional Growth of Bone

18. Bone Formation Of MandibleBone Formation Of Mandible

19. Factors affecting bone growth andFactors affecting bone growth and
remodelingremodeling
 A lot of bone remodeling is a result ofA lot of bone remodeling is a result of
hormonal action.hormonal action.
 Hormones involved in bone growth andHormones involved in bone growth and
remodeling isremodeling is PTHPTH andand CalcitoninCalcitonin
 CalcitoninCalcitonin is released by the thyroidis released by the thyroid
gland that decreases osteoclasts yieldinggland that decreases osteoclasts yielding
decreased mobilization of calcium fromdecreased mobilization of calcium from
bone and decreasing blood calciumbone and decreasing blood calcium
concentrationsconcentrations

20. QUESTIONSQUESTIONS

21. THANK YOUTHANK YOU