ch 06 lecture outline b
TRANSCRIPT
PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College
C H A P T E R
Copyright © 2010 Pearson Education, Inc.
6
Bones and Skeletal Tissues: Part B
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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
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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)
Mesenchymalcell
CollagenfiberOssificationcenter
Osteoid
Osteoblast
Ossification centers appear in the fibrousconnective tissue membrane.• Selected centrally located mesenchymal cells cluster
and differentiate into osteoblasts, forming anossification center.
1
Copyright © 2010 Pearson Education, Inc. Figure 6.8, (2 of 4)
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
Copyright © 2010 Pearson Education, Inc. Figure 6.8, (3 of 4)
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
Copyright © 2010 Pearson Education, Inc. Figure 6.8, (4 of 4)
FibrousperiosteumOsteoblast
Plate ofcompact bone
Diploë (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
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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 cartilage
Week 9
Bone collar
Primaryossificationcenter
Copyright © 2010 Pearson Education, Inc. Figure 6.9, step 2
Cartilage in the centerof the diaphysis calcifiesand then develops cavities.
2
Area of deterioratingcartilage matrix
Copyright © 2010 Pearson Education, Inc. Figure 6.9, step 3
The periosteal bud inavadesthe internal cavities andspongy bone begins to form.
3
Spongyboneformation
Bloodvessel ofperiostealbud
Month 3
Copyright © 2010 Pearson Education, Inc. Figure 6.9, step 4
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
Copyright © 2010 Pearson Education, Inc. Figure 6.9, step 5
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
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
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Postnatal Bone Growth
• Interstitial growth:
• length of long bones
• Appositional growth:
• thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces
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Growth in Length of Long Bones
• Epiphyseal plate cartilage organizes into four important functional zones:
• Proliferation (growth)
• Hypertrophic
• Calcification
• Ossification (osteogenic)
Copyright © 2010 Pearson Education, Inc. Figure 6.10
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
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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
Copyright © 2010 Pearson Education, Inc. Figure 6.11
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.
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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
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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
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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
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Control of Remodeling
•What controls continual remodeling of bone?
• Hormonal mechanisms that maintain calcium homeostasis in the blood
• Mechanical and gravitational forces
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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
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Hormonal Control of Blood Ca2+
• 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
Copyright © 2010 Pearson Education, Inc. Figure 6.12
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
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Hormonal Control of Blood Ca2+
• 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
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Response to Mechanical Stress
• Wolff’s law: A bone grows or remodels in response to forces or demands placed upon it
• Observations supporting Wolff’s law:
• Handedness (right or left handed) results in bone of one upper limb being thicker and stronger
• Curved bones are thickest where they are most likely to buckle
• Trabeculae form along lines of stress
• Large, bony projections occur where heavy, active muscles attach
Copyright © 2010 Pearson Education, Inc. Figure 6.13
Load here (body weight)
Head offemur
Compressionhere
Point ofno stress
Tensionhere
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Classification of Bone Fractures
• Bone fractures may be classified by four “either/or” classifications:
1. Position of bone ends after fracture:
• Nondisplaced—ends retain normal position
• Displaced—ends out of normal alignment
2. Completeness of the break
• Complete—broken all the way through
• Incomplete—not broken all the way through
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Classification of Bone Fractures
3. Orientation of the break to the long axis of the bone:
• Linear—parallel to long axis of the bone
• Transverse—perpendicular to long axis of the bone
4. Whether or not the bone ends penetrate the skin:
• Compound (open)—bone ends penetrate the skin
• Simple (closed)—bone ends do not penetrate the skin
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Common Types of Fractures
• All fractures can be described in terms of
• Location
• External appearance
• Nature of the break
Copyright © 2010 Pearson Education, Inc. Table 6.2
Copyright © 2010 Pearson Education, Inc. Table 6.2
Copyright © 2010 Pearson Education, Inc. Table 6.2
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Stages in the Healing of a Bone Fracture
1. Hematoma forms
• Torn blood vessels hemorrhage
• Clot (hematoma) forms
• Site becomes swollen, painful, and inflamed
Copyright © 2010 Pearson Education, Inc. Figure 6.15, step 1
A hematoma forms.1
Hematoma
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Stages in the Healing of a Bone Fracture
2. Fibrocartilaginous callus forms
• Phagocytic cells clear debris
• Osteoblasts begin forming spongy bone within 1 week
• Fibroblasts secrete collagen fibers to connect bone ends
• Mass of repair tissue now called fibrocartilaginous callus
Copyright © 2010 Pearson Education, Inc. Figure 6.15, step 2
Fibrocartilaginouscallus forms.2
Externalcallus
Newbloodvessels
Spongybonetrabecula
Internalcallus(fibroustissue andcartilage)
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Stages in the Healing of a Bone Fracture
3. Bony callus formation
• New trabeculae form a bony (hard) callus
• Bony callus formation continues until firm union is formed in ~2 months
Copyright © 2010 Pearson Education, Inc. Figure 6.15, step 3
Bony callus forms.3
Bonycallus ofspongybone
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Stages in the Healing of a Bone Fracture
4. Bone remodeling
• In response to mechanical stressors over several months
• Final structure resembles original
Copyright © 2010 Pearson Education, Inc. Figure 6.15, step 4
Bone remodelingoccurs.4
Healedfracture
Copyright © 2010 Pearson Education, Inc. Figure 6.15
Hematoma Externalcallus
Bonycallus ofspongyboneHealedfracture
Newbloodvessels
Spongybonetrabecula
Internalcallus(fibroustissue andcartilage)
A hematoma forms. Fibrocartilaginouscallus forms.
Bony callus forms. Boneremodelingoccurs.
1 2 3 4
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Homeostatic Imbalances
• Osteomalacia and rickets
• Calcium salts not deposited
• Rickets (childhood disease) causes bowed legs and other bone deformities
• Cause: vitamin D deficiency or insufficient dietary calcium
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Homeostatic Imbalances
• Osteoporosis
• Loss of bone mass—bone resorption outpaces deposit
• Spongy bone of spine and neck of femur become most susceptible to fracture
• Risk factors
• Lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus
Copyright © 2010 Pearson Education, Inc. Figure 6.16
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Osteoporosis: Treatment and Prevention
• Calcium, vitamin D, and fluoride supplements
• Weight-bearing exercise throughout life
• Hormone (estrogen) replacement therapy (HRT) slows bone loss
• Some drugs (Fosamax, SERMs, statins) increase bone mineral density
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Paget’s Disease
• Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull
• Pagetic bone has very high ratio of spongy to compact bone and reduced mineralization
• Unknown cause (possibly viral)
• Treatment includes calcitonin and biphosphonates
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Developmental Aspects of Bones
• Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms
• At birth, most long bones are well ossified (except epiphyses)
Copyright © 2010 Pearson Education, Inc. Figure 6.17
Parietal bone
Radius
Ulna
Humerus
Femur
Occipital bone
ClavicleScapula
Ribs
Vertebra
Ilium
Tibia
Frontal boneof skull
Mandible
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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