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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

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Bones and Skeletal Tissues: Part B


Bone Development

• Osteogenesis (ossification)—bone tissue formation

• Stages• Bone formation—begins in the 2nd month of

development

• Postnatal bone growth—until early adulthood

• Bone remodeling and repair—lifelong


Two Types of Ossification

1. Intramembranous ossification• Membrane bone develops from fibrous

membrane• Forms flat bones, e.g. clavicles and cranial

bones

2. Endochondral ossification• Cartilage (endochondral) bone forms by

replacing hyaline cartilage• Forms most of the rest of the skeleton

Copyright © 2010 Pearson Education, Inc. Figure 6.8, (1 of 4)

MesenchymalcellCollagenfiberOssificationcenterOsteoid

Osteoblast Ossification centers appear in the fibrousconnective tissue membrane.• Selected centrally located mesenchymal cells cluster

and differentiate into osteoblasts, forming anossification center.

1


Osteoid

Osteocyte

Newly calcifiedbone matrix

Osteoblast

Bone matrix (osteoid) is secreted within thefibrous membrane and calcifies.• Osteoblasts begin to secrete osteoid, which is calcified

within a few days.• Trapped osteoblasts become osteocytes.

2


Mesenchymecondensingto form theperiosteum

Blood vessel

Trabeculae ofwoven bone

Woven bone and periosteum form.• Accumulating osteoid is laid down between embryonic

blood vessels in a random manner. The result is a network(instead of lamellae) of trabeculae called woven bone.

• Vascularized mesenchyme condenses on the external faceof the woven bone and becomes the periosteum.

3


FibrousperiosteumOsteoblast

Plate ofcompact boneDiploë (spongybone) cavitiescontain redmarrow

Lamellar bone replaces woven bone, just deep tothe periosteum. Red marrow appears.• Trabeculae just deep to the periosteum thicken, and are later

replaced with mature lamellar bone, forming compact boneplates.

• Spongy bone (diploë), consisting of distinct trabeculae, per-sists internally and its vascular tissue becomes red marrow.

4


Endochondral Ossification

• Uses hyaline cartilage models

• Requires breakdown of hyaline cartilage prior to ossification

Copyright © 2010 Pearson Education, Inc. Figure 6.9

Bone collarforms aroundhyaline cartilagemodel.

Cartilage in thecenter of thediaphysis calcifiesand then developscavities.

The periostealbud inavades theinternal cavitiesand spongy bonebegins to form.

The diaphysis elongatesand a medullary cavityforms as ossificationcontinues. Secondaryossification centers appearin the epiphyses inpreparation for stage 5.

The epiphysesossify. Whencompleted, hyalinecartilage remains onlyin the epiphysealplates and articularcartilages.

Hyalinecartilage

Area ofdeterioratingcartilage matrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificationcenter

Bloodvessel ofperiostealbud

Medullarycavity

Articularcartilage

Childhood toadolescence

BirthWeek 9 Month 3

Spongybone

BonecollarPrimaryossificationcenter

1 2 3 4 5

Copyright © 2010 Pearson Education, Inc. Figure 6.9, step 1

Bone collar forms aroundhyaline cartilage model.1

Hyaline cartilageWeek 9

Bone collar

Primaryossificationcenter


Cartilage in the centerof the diaphysis calcifiesand then develops cavities.

2

Area of deterioratingcartilage matrix


The periosteal bud inavadesthe internal cavities andspongy bone begins to form.

3

Spongyboneformation


Month 3


The diaphysis elongates and a medullary cavity formsas ossification continues. Secondary ossification centersappear in the epiphyses in preparation for stage 5.

4

Epiphysealblood vessel Secondary

ossificationcenter

Medullarycavity

Birth


The epiphyses ossify. When completed, hyaline cartilageremains only in the epiphyseal plates and articular cartilages.5

Epiphyseal platecartilage

Articular cartilage

Childhood to adolescence

Spongy bone


Bone collarforms aroundhyaline cartilagemodel.

Cartilage in thecenter of thediaphysis calcifiesand then developscavities.

The periostealbud inavades theinternal cavitiesand spongy bonebegins to form.

The diaphysis elongatesand a medullary cavityforms as ossificationcontinues. Secondaryossification centers appearin the epiphyses inpreparation for stage 5.

The epiphysesossify. Whencompleted, hyalinecartilage remains onlyin the epiphysealplates and articularcartilages.

Hyalinecartilage

Area ofdeterioratingcartilage matrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificationcenter


Medullarycavity

Articularcartilage

Childhood toadolescence

BirthWeek 9 Month 3

Spongybone

BonecollarPrimaryossificationcenter

1 2 3 4 5


Postnatal Bone Growth

• Interstitial growth: • length of long bones

• Appositional growth: • thickness and remodeling of all bones by

osteoblasts and osteoclasts on bone surfaces


Growth in Length of Long Bones

• Epiphyseal plate cartilage organizes into four important functional zones: • Proliferation (growth)

• Hypertrophic

• Calcification

• Ossification (osteogenic)


Calcified cartilagespicule

Osseous tissue(bone) coveringcartilage spicules

Resting zone

Osteoblast depositingbone matrix

Proliferation zoneCartilage cells undergo mitosis.

Hypertrophic zoneOlder cartilage cells enlarge.

Ossification zoneNew bone formation is occurring.

Calcification zoneMatrix becomes calcified; cartilage cells die; matrix begins deteriorating.

1

2

3

4


Hormonal Regulation of Bone Growth

• Growth hormone stimulates epiphyseal plate activity

• Thyroid hormone modulates activity of growth hormone

• Testosterone and estrogens (at puberty)• Promote adolescent growth spurts

• End growth by inducing epiphyseal plate closure


Bone growth Bone remodeling

Articular cartilage

Epiphyseal plate

Cartilagegrows here.

Cartilageis replacedby bone here.Cartilagegrows here.

Bone isresorbed here.

Bone isresorbed here.

Bone is addedby appositionalgrowth here. Cartilage

is replacedby bone here.


Bone Deposit

• Occurs where bone is injured or added strength is needed

• Requires a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese


Bone Deposit

• Sites of new matrix deposit are revealedby the• Osteoid seam

• Unmineralized band of matrix

• Calcification front

• The abrupt transition zone between the osteoid seam and the older mineralized bone


Bone Resorption

• Osteoclasts secrete• Lysosomal enzymes (digest organic matrix)

• Acids (convert calcium salts into soluble forms)

• Dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood


Control of Remodeling

•What controls continual remodeling of bone?• Hormonal mechanisms that maintain calcium

homeostasis in the blood

• Mechanical and gravitational forces


Hormonal Control of Blood Ca2+

• Calcium is necessary for• Transmission of nerve impulses

• Muscle contraction

• Blood coagulation

• Secretion by glands and nerve cells

• Cell division



• Primarily controlled by parathyroid hormone (PTH)

Blood Ca2+ levels

Parathyroid glands release PTH

PTH stimulates osteoclasts to degrade bone matrix and release Ca2+

Blood Ca2+ levels


Osteoclastsdegrade bonematrix and release Ca2+

into blood.

Parathyroidglands

Thyroidgland

Parathyroidglands releaseparathyroidhormone (PTH).

StimulusFalling bloodCa2+ levels

PTH

Calcium homeostasis of blood: 9–11 mg/100 mlBALANCEBALANCE



• May be affected to a lesser extent by calcitonin Blood Ca2+ levels

Parafollicular cells of thyroid release calcitonin

Osteoblasts deposit calcium salts

Blood Ca2+ levels• Leptin has also been shown to influence bone

density by inhibiting osteoblasts


Developmental Aspects of Bones

• Nearly all bones completely ossified by age 25

• Bone mass decreases with age beginning in 4th decade

• Rate of loss determined by genetics and environmental factors

• In old age, bone resorption predominates

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