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C H A P T E R
6Bones andSkeletal Tissues
The skeletal system
• Components :• Bones of the skeleton• Cartilages• Ligaments• Other connective tissues that stabilize and connect
• Functions :• Support – provides hard framework• Movement – skeletal muscles use bones as levers• Protection of underlying organs• Mineral storage – reservoir for important minerals• Blood-cell formation – bone contains red marrow
Cartilage • Resist compression and tension• Cartilage, firm but flexible and cells separated by abundant
extracellular matrix (holds 80% water)- no blood vessels or nerves. • Chondrocytes• Lacunae• Chondroblasts• perichondrium
• Hyaline cartilage – (glass) – most abundant cartilage• Provides support through flexibility
• Elastic cartilage – contains many elastic fibers• Able to tolerate repeated bending
• Fibrocartilage – resists strong compression and strong tension• An intermediate between hyaline and elastic cartilage
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Cartilage inexternal ear
Cartilages innose
Articular cartilageof a joint
Costal cartilageCartilagein intervertebraldisc
CartilageEpiglottis
Larynx
Trachea
Cricoidcartilage
Lung
Thyroidcartilage
Hyaline cartilages
Elastic cartilages
Fibrocartilages
Cartilages
Pubicsymphysis
Articular cartilageof a joint
Meniscus (padlikecartilage inknee joint) Respiratory
tube cartilagesin neck and thorax
Gelatinous groundsubstance
Chondrocyte in a lacunaElastic fibers
Lacuna
Matrix
Chondrocytein a lacuna
Perichondrium
(a) Hyaline cartilage (180×)
Cartilages in the Adult Body
Chondrocyte in a lacuna
Collagen fibers
(b) Elastic cartilage (470×)
(c) Fibrocartilage (285×)Figure 6.2
Classification of Bones
• Long bones – longer than wide – a shaft plus ends• Short bones – roughly cube-shaped• Flat bones – thin and flattened, usually curved• Irregular bones – various shapes, do not fit into
other categories
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Classification of Bones
Figure 6.3
Cells in bone
• Osteocytes = mature bone cells• In lacunae, Connected by canaliculi• Osteoblasts synthesize new matrix (Osteogenesis)• Osteoclasts dissolve bone matrix (Osteolysis)• Osteoprogenitor cells differentiate into
osteoblasts
Gross Anatomy of Bones
• Compact bone – dense outer layer of bone• Spongy (cancellous) bone – internal network of
bone
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Structure of a Long Bone
Proximalepiphysis
(b)
EndosteumEpiphysealline
Articular cartilage
Periosteum
Spongy bone
Compact boneMedullarycavity (lined
Compact bone
Endosteum
Figure 6.4a–c
(b)
(c)(a)
Yellowbone marrow
by endosteum)
Compact bone
Periosteum
Perforating(Sharpey’s)fibersNutrientarteries
Diaphysis
Distalepiphysis
Spongy bone(di l ë)
Structure of Short, Irregular, and Flat Bones
• Flat bones, short bones, and irregular bones• Contain bone
marrow but noCompact bone
Trabeculae
(diploë)
Figure 6.5
marrow but no marrow cavity
• Diploë• Internal spongy
bone of flat bones
Load here(body weight)
Head offemur
Gross Anatomy of Bones
• Bone design and stress• Anatomy of a bone
reflects stresses• Compression and tension
greatest at external
Compressionhere
Point of no stress
Tensionhere
(a)
greatest at external surfaces
Figure 6.6a
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Gross Anatomy of Bones
Compact bone
Endosteum lining bony canals and covering trabeculae
Perforating (Volkmann’s) canal
Circumferentiallamellae
Osteon(Haversian system)
Central(Haversian) canal
Spongy bone
Microscopic Structure of Compact Bones
Figure 6.7
(a)Perforating (Sharpey’s) fibersPeriosteal blood vesselPeriosteum
Lamellae
(c)Interstitial lamellae
Lacunae
LamellaeCentralcanal
Lacuna (with osteocyte) (b)
NerveVeinArtery
CanaliculiOsteocytein a lacuna
Lacunae
LamellaeCentral canal
Structuresin thecentralcanal
Artery withcapillaries
VeinNerve fiber
Lamellae
Collagenfibers
Microscopic Structure of Compact Bones
run indifferentdirections
Twistingforce
Figure 6.8
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Trabecula
Osteocytes
Marrow space
Microscopic Structure of Spongy Bone
Endosteum
(b)
(a)Osteoblasts
Figure 6.9
Chemical Composition of Bone
• 35% organic components• Composed of cells, fibers, and organic substances• Collagen – abundant
• 65% inorganic mineral salts• Primarily calcium phosphate• Resists compression
Bone Development
• Ossification (osteogenesis) – bone-tissue formation• Membrane bones – formed directly from
mesenchyme• Intramembranous ossification
• Other bones – develop initially from hyalineOther bones develop initially from hyaline cartilage• Endochondral ossification
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Intramembranous Ossification
MesenchymalcellCollagenfiberOssificationcenter
Osteoid
Osteocyte
Osteoblast
Figure 6.10, steps 1–2
center
Osteoid
Osteoblast
Newly calcifiedbone matrix
Ossification centers appear in the fibrous connective tissue membrane.• Selected centrally located mesenchymal cells cluster
and differentiate into osteoblasts, forming an ossification center.
Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies.• Osteoblasts begin to secrete osteoid, which is
calcified within a few days.• Trapped osteoblasts become osteocytes.
1 2
Intramembranous Ossification
Mesenchymecondensingto form theperiosteum
Blood vessel
Trabeculae ofwoven bone
FibrousperiosteumOsteoblast
Plate ofcompact bone
Diploë (spongybone) cavities
Figure 6.10, steps 3–4
Blood vessel bone) cavitiescontain redmarrow
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 calledwoven bone.
• Vascularized mesenchyme condenses on the externalface of the woven bone and becomes the periosteum.
Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken and
are later replaced with mature lamellar bone, forming compact bone plates.
• Spongy bone (diploë), consisting of distinct trabeculae, persists internally, and its vascular tissue becomes red marrow.
3 4
Hyalinecartilage
Area ofdeterioratingcartilage matrix
Epiphysealblood vessel
Epiphysealplatecartilage
Secondaryossificationcenter
Medullary
Articularcartilage
Childhood to adolescenceBirthWeek 9 Month 3
Spongybone
Stages in Endochondral Ossification
cartilageSpongyboneformation
Bloodvessel ofperiostealbud
Medullarycavity
Bone collarPrimaryossificationcenter
Bone collar forms around hyaline cartilage model.
Cartilage in the center of the diaphysis calcifies and then develops cavities.
The periosteal bud invades the internal cavities, and spongy bone begins to form.
The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5.
The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.
1 2 3 4 5
Figure 6.11
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Growth of Endochondral Bones• Appositional growth – growth of a bone by addition
of bone tissue to its surface
Hormonal Regulation of Bone Growth
• Growth hormone – produced by the pituitary gland• Stimulates epiphyseal plates
• Thyroid hormone – ensures that the skeleton t i tiretains proper proportions
• Sex hormones• Promote bone growth• Later induces closure of epiphyseal plates
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Bones are Continuously changing
• Bone deposit and removal• Occurs at periosteal and endosteal surfaces• Bone deposition – accomplished by osteoblasts• Bone reabsorption – accomplished by osteoclast
• Bone remodeling• Helps maintain constant concentration of Ca2+ andHelps maintain constant concentration of Ca and
PO43-
• PTH and calcitonin affect osteoclast activity• Response to mechanical stress
Repair of Bone Fractures
• Simple and compound fractures• Treatment by reduction
• Closed reduction• Open reduction
Stages of Healing a Fracture
Hematoma Externalcallus
NewInternal
Bonycallus ofspongyboneH l d
Figure 6.15
Newbloodvessels
Spongybonetrabecula
Internalcallus(fibroustissue andcartilage)
A hematoma forms. Fibrocartilaginous callus forms.
Bony callus forms.
Healedfracture
Bone remodeling occurs.
1 2 3 4
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Common Types of Fractures
Table 6.2 (1 of 3)
Common Types of Fractures
Table 6.2 (2 of 3)
Common Types of Fractures
Table 6.2 (3 of 3)
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Disorders of Bones
• Osteoporosis – characterized by low bone mass• Bone reabsorption outpaces bone deposition• Occurs most of in women after menopause
Figure 6.16
Disorders of Bones
• Osteomalacia – occurs in adults – bones are inadequately mineralized• Rickets – occurs in children – analogous to
osteomalacia • Paget's disease characterized by excessive rate• Paget's disease – characterized by excessive rate
of bone deposition • Osteosarcoma – a form of bone cancer
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