Growth and Growth and Development of BoneDevelopment of Bone

IntroductionIntroduction

Bone is a relatively hard and lightweight Bone is a relatively hard and lightweight composite material, formed mostly of composite material, formed mostly of calcium phosphate calcium phosphate

Bone can be either Bone can be either compactcompact or or cancellouscancellous (spongy). (spongy). CorticalCortical (outer (outer layer) bone is compact layer) bone is compact

Cortical bone accounts for 80% of the total Cortical bone accounts for 80% of the total bone mass of the adult skeleton bone mass of the adult skeleton

Types Of BonesTypes Of Bones

Long BonesLong Bones Short BonesShort Bones Flat BonesFlat Bones Irregular BonesIrregular Bones Pneumatic BonesPneumatic Bones Sessamoid BonesSessamoid Bones

Bone cellsBone cells OsteoblastsOsteoblasts are typically viewed as bone forming cells. are typically viewed as bone forming cells. OsteocytesOsteocytes originate from osteoblasts which have originate from osteoblasts which have

migrated into and become trapped and surrounded by migrated 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 bone are the cells responsible for bone resorption. Osteoclasts are large, multinucleated cells resorption. Osteoclasts are large, multinucleated cells located on bone surfaceslocated on bone surfaces

Lining Cells Lining Cells come from osteoblasts which have become come from osteoblasts which have become flattenedflattened. . Bone lining cells have flat organelles so they Bone lining cells have flat organelles so they can easily cover the bone without interfering with other can easily cover the bone without interfering with other cells functionscells functions. .

Developmental ClassificationDevelopmental Classification Membranous BonesMembranous Bones ossify in membrane ossify 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 cartilage ossify 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 in ossify partly in membrane and partly in cartilage. Eg. Clavicle, Mandible, membrane and partly in cartilage. Eg. Clavicle, Mandible, Occipital, Temporal, SphenoidOccipital, Temporal, Sphenoid

Intramembranous OssificationIntramembranous Ossification

Intramembranous ossificationIntramembranous ossification  is one of is one of the two essential processes the two essential processes duringduring  fetalfetal  development of the development of the skeletal skeletal systemsystem  by which rudimentaryby which rudimentary  bone bone tissuetissue  is created.is created.

Stages of Intramembranous Stages of Intramembranous OssificationOssification

Stages of Intramembranous Stages of Intramembranous OssificationOssification

Stages of Intramembranous Stages of Intramembranous OssificationOssification

Stages of Intramembranous Stages of Intramembranous OssificationOssification

Endochondral OssificationEndochondral Ossification

Begins in the second month of Begins in the second month of developmentdevelopment

Uses hyaline cartilage “bones” as models Uses hyaline cartilage “bones” as models for bone constructionfor bone construction

Requires breakdown of hyaline cartilage Requires breakdown of hyaline cartilage prior to ossificationprior to ossification

Formation of bone collar around hyaline cartilage model.

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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 periosteal bud

Secondary ossification centerEpiphyseal

blood vessel

Medullary cavity

Epiphyseal plate cartilage

Spongy bone

Articular cartilage

Stages of Endochondral OssificationStages of Endochondral Ossification

Bone ResorptionBone Resorption While osteoblasts and osteocytes are adding While osteoblasts and osteocytes are adding

new bone to the outer surface, osteoclasts are new bone to the outer surface, osteoclasts are removing bone at the inner surface and removing bone at the inner surface and enlarging the marrow cavityenlarging the marrow cavity

Osteoclasts make contact with the bone through Osteoclasts make contact with the bone through a region referred to as ruffled border and a region referred to as ruffled border and subsequently have the ability to degrade both subsequently have the ability to degrade both inorganic and organic matrices of the boneinorganic and organic matrices of the bone

Types of MarrowTypes of Marrow

Red marrow – chief blood cell forming Red marrow – chief blood cell forming organ of the adult and is found in spongy organ of the adult and is found in spongy bone of the epiphysis of long bones and bone of the epiphysis of long bones and main bodies of ribs, sternum and main bodies of ribs, sternum and vertebraevertebrae

Yellow marrow – composed mainly of Yellow marrow – composed mainly of adipose tissue and found in the medullary adipose tissue and found in the medullary cavity of bonescavity of bones

Bone RemodelingBone Remodeling Osteoblasts form osteons (basic functional unit of Osteoblasts form osteons (basic functional unit of

compact bone) by osteogenesis whereas osteoclasts compact bone) by osteogenesis whereas osteoclasts destroy osteons by resorption. destroy osteons by resorption.

The balance between these two yields net bone The balance between these two yields net bone depositiondeposition

As animals age, bone resorption may exceed formation As 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 or Formation of new bone on the surface of older bone or cartilagecartilage

Long Bone Growth and RemodelingLong Bone Growth and Remodeling

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 canalCentral canal of osteonPeriosteal ridge

Appositional Growth of BoneAppositional Growth of Bone

Bone Formation Of MandibleBone Formation Of Mandible

Factors affecting bone growth and Factors affecting bone growth and remodelingremodeling

A lot of bone remodeling is a result of A lot of bone remodeling is a result of hormonal action.hormonal action.

Hormones involved in bone growth and Hormones involved in bone growth and remodeling is remodeling is PTHPTH and and CalcitoninCalcitonin

CalcitoninCalcitonin is released by the thyroid gland is released by the thyroid gland that decreases osteoclasts yielding that decreases osteoclasts yielding decreased mobilization of calcium from decreased mobilization of calcium from bone and decreasing blood calcium bone and decreasing blood calcium concentrationsconcentrations

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