Skeletal system

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Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc publishing as Benjamin Cummings. Lecture 6 THE SKELETAL SYSTEM – Bones and Cartilage

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Transcript of Skeletal system

Page 1: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Lecture 6

THE SKELETAL SYSTEM – Bones and Cartilage

Page 2: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.1: The bones and cartilages of the human skeleton, p. 177.

Epiglottis

Larynx

TracheaLung

Respiratorytube cartilagesin neck and thorax

= Hyaline cartilages

Key:

= Fibrocartilages

= Elastic cartilages

= Bones of axial skeleton

= Bones of appendicular skeleton

Cartilage inexternal ear

Cartilages in nose

Articularcartilageof a joint

Costalcartilage

Cartilage in intervertebraldisc

Pubicsymphysis

Articular cartilageof a joint

Meniscus (padlike cartilage in knee joint)

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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.2: Classification of bones on the basis of shape, p. 178.

(a)

(b)

(d)

(c)

Long bone (humerus)

Short bone (triquetral)

Irregular bone (vertebra),left lateral view

Flat bone (sternum)

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2 Types of Bone Tissue

Spongy bone

Compact bone

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2 types of bone tissue• Compact bone tissue - composed of OSTEONS =

structural units of compact bone.

• Spongy bone tissue – like a honeycomb – composed of needle-like structures called TRABECULAE = structural units of spongy bone

Compact bone

Spongy bone

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Structure of a long bone• Epiphyses = expanded ends of long bones

spongy bone surrounded by a thin layer of compact bone

• Diaphysis = shaft = long axis of a long bone composed of a thick collar of compact bone which surrounds a

Medullary Cavity – contains red bone marrow in childhood and yellow bone marrow in adulthood

Hematopoiesis, the process by which blood cells and platelets are formed, occurs only in red bone marrow

Membranes: Endosteum and Periosteum

Page 7: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.3: The structure of a long bone (humerus of arm), p. 180.

(b)

(c)(a)

Proximalepiphysis

Articularcartilage

Yellowbone marrow

Endosteum

Epiphysealline

Spongybone

Periosteum

Compact bone

Medullarycavity

Spongy bone

Compact bone

Articularcartilage

Compact bone

Periosteum

Perforating(Sharpey’s)fibersNutrientarteries

Diaphysis

Distalepiphysis

Page 8: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.3a: The structure of a long bone (humerus of arm), p. 180.

(a)

Proximalepiphysis

ArticularcartilageEpiphysealline

Spongybone

Periosteum

Compact boneMedullarycavity

Diaphysis

Distalepiphysis

Fat

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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.6: Microscopic anatomy of compact bone, p. 183.

(a)

(b)

(c)

Perforating(Sharpe’s)fibersCompactbone

Periostealblood vessel

Periosteum

Lacuna

Blood vesselEndosteum lining bony canals and covering trabeculae

Central (Haversian) canal

Spongy bone

Blood vessel continuesinto medullary cavitycontaining marrow

Central (Haversian) canalCanaliculus

Lacuna

Lamella

Osteocyte

Osteon(Haversian system)

Circumferentiallamellae

Lamellae

Osteon

Interstitiallamellae

Centralcanal

Perforating (Volkmann’s) canal

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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.5: A single osteon, p. 182.

Lamellae

Collagenfibers

Twistingforce

Nerve fiber

Vein

Artery withcapillaries

Structuresin thecentralcanal

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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.3c: The structure of a long bone (humerus of arm), p. 180.

(c)

Yellowbone marrow

Endosteum

Compact bone

PeriosteumPerforating(Sharpey’s)fibersNutrientarteries

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The 2 membranes• Endosteum: covers the internal surfaces

of bone such as the canals. It contains osteoblasts and osteoclasts

• Periosteum: is double-layered – composed of the outer fibrous layer and the inner osteogenic layer.

• The fibrous layer is composed of dense irregular connective tissue

• The osteogenic layer contains of osteoblasts and osteoclasts.

• The periosteum is attached to compact bone by tough collagenous fibers called the

SHARPEY”S(perforating) FIBERS

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The bone cells• Osteoblasts: bone-forming cells – secrete bone

tissue

• Osteogenic cells: give rise to osteoblasts

• Osteocytes: matured osteoblasts

• Osteoclasts: bone-resorbing cells – destroy bone tissue

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Microscopic structure of compact bone• Composed of osteons= structural units of compact bone• Each osteon is an elongated cylinder consisting of concentric tubes called

LAMELLAE hence, compact bone is also known as Lamellar bone. The collagen fibers in adjacent lamellae run in opposite directions to resist twisting

• HAVERSIAN CANAL = Central canal – runs in the core of each osteon contains blood vessels and nerves

• Perforating or Volkmann’s canals – connect blood vessels and nerves between the periosteum and the Haversian canals

• LACUNAE – shallow cavities in the solid bone matrix that house the osteocytes.

• CANALICULI – tiny canals that connect lacunae to each other and to the Haversian canal to allow for transfer of substances from the blood vessel in the Haversian canal

Page 15: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.6a: Microscopic anatomy of compact bone, p. 183.

(a)

Perforating(Sharpey’s)fibers

Compactbone

Periostealblood vessel

Periosteum

Blood vesselEndosteum lining bony canals and covering trabeculae

Central (Haversian) canal

Spongy bone

Blood vessel continuesinto medullary cavitycontaining marrow

Osteon(Haversian system)

CircumferentiallamellaeLamellae

Perforating (Volkmann’s) canal

Page 16: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.15: Fetal primary ossification centers at 12 weeks, p. 198.

Parietalbone

Radius

Ulna

Humerus

Femur

Occipitalbone

Clavicle

Scapula

Ribs

Vertebra

Ilium

Tibia

Frontalbone ofskullMandible

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OSSIFICATION ( Osteogenesis) - Development of the bony skeleton from the embryonic skeleton

• 2 forms: PRENATAL AND POSTNATAL

• Prenatal bone development – occurs before birth; 2 types

i) INTRAMEMBRANOUS OSSIFICATION ii)ENDOCHONDRAL OSSIFICATION

Intramembranous ossification: develops from FIBROUS CONNECTIVE TISSUE MEMBRANE

( derived directly from mesenchyme) and results in the formation of MEMBRANE BONES = cranial bones and clavicles

Note: all membrane bones are flat bones.

Page 18: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.7: Intramembranous ossification, p. 184.

Mesenchymal cell

Collagen fiber

Ossification center

Osteoid

Osteoblast

OsteoidOsteocyte

Newly calcifiedbone matrix

Osteoblast

An ossification center appears in the fibrous connectivetissue membrane.•Selected centrally located mesenchymal cells cluster anddifferentiate into osteoblasts, forming an ossification center.

Bone matrix (osteoid) is secreted within the fibrousmembrane.• Osteoblasts begin to secrete osteoid, which is mineralized within a few days.• Trapped osteoblasts become osteocytes.

1

2

Page 19: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.7: Intramembranous ossification (continued), p. 184.

MesenchymeCondensingto form theperiosteum

Blood vessel

Trabecula ofwoven bone

Fibrousperiosteum

Osteoblast

Plate ofcompact boneDiploë (spongy bone)cavities contain redmarrow

Woven bone and periosteum form.• Accumulating osteoid is laid down between embryonic blood vessels, which form a random network. The result is a network (instead of lamellae) of trabeculae.• Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum.

Bone collar of compact bone forms and red marrow appears.• Trabeculae just deep to the periosteum thicken, forming a woven bone collar that is later replaced with mature lamellar bone.• Spongy bone (diploë), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow.

3

4

Intramembranous ossification: develops from FIBROUS CT MEMBRANE ( derived directly from mesenchyme) and results in the formation of MEMBRANE BONES = cranial bones and clavicles

Note: all membrane bones are flat bones.

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The Embryonic Skeleton

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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.8: Endochondral ossification in a long bone, p. 185.

Formation ofbone collararound hyalinecartilage model.

Hyalinecartilage

Cavitation ofthe hyaline carti-lage within thecartilage model.

Invasion ofinternal cavitiesby the periostealbud and spongybone formation.

Formation of themedullary cavity asossification continues;appearance of sec-ondary ossificationcenters in the epiphy-ses in preparationfor stage 5.

Ossification of theepiphyses; whencompleted, hyalinecartilage remains onlyin the epiphyseal platesand articular cartilages.

Deterioratingcartilagematrix

Epiphysealblood vessel

Spongyboneformation

Epiphysealplatecartilage

Secondaryossificatoncenter

Bloodvessel ofperiostealbud

Medullarycavity

ArticularcartilageSpongybone

Primaryossificationcenter

Bone collar

1

2

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5

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• Derived from HYALINE CARTILAGE produced by chondroblasts; (chondroblasts are

derived from mesenchyme)

The bones formed from endochondral ossification are called endochondral or cartilage bones = all bones in the body except the cranial bones and the clavicles

Endochondral Ossification

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Endochondral Ossification• Hyaline cartilage is ossified into bone.

• After endochondral ossification, hyaline cartilage still persists in two areas in the long bones as the:

1. Articular cartilage – capping the ends of the epiphyses of long bones

2. Epiphyseal plates = at the junctions of the epiphyses and the diaphysis of a long

bone

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Postnatal Bone Growth• Ossification that occurs after birth• 2 types: Longitudinal bone growth and

Appositional bone growth

• Longitudinal bone growth = Linear bone growth increases the length of long bones = height

• Appositional bone growth = increases the width/diameter of all bones

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LONGITUDINAL Bone Growth

• Involves the EPIPHYSEAL PLATES• New hyaline cartilage is added on at the

epiphyseal faces of the epihyseal plates

• New bone tissue is added on at the diaphyseal faces of the epiphyseal plates

• Results in lengthening of the diaphysis of the long bone = lengthening of the long bone

• The amount of new hyaline cartilage added on the epiphyseal face = the amount of bone tissue formed on the diaphyseal face hence, the width ( thickness) of the epiphyseal plates does NOT change

Page 26: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.9: Growth in length of a long bone – zones of the Epiphyseal plate

Calcifiedcartilagespicule

Osseoustissue (bone)coveringcartilagespicules

Growth (proliferation)zoneCartilage cellsundergo mitosis

Resting (quiescent) zone

Hypertrophic zoneOlder cartilagecells enlarge

Ossification (osteogenic)zoneNew boneformationis occurring

Resorption zone

Calcification zoneMatrix becomescalcified; cartilagecells die; matrix begins deteriorating

Osteoblastdepositingbone matrix

Diaphyseal face

Epiphyseal face

Page 27: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.10: Long bone growth and remodeling during youth, p. 187.

Growth

Bone grows inlength because:

Cartilagegrows here

Cartilagegrows here

Cartilagereplaced bybone here

Cartilagereplaced bybone here

Remodeling

Growing shaftis remodeled by:

Articularcartilage

Boneresorbedhere

Boneadded byappositionalgrowth here

Boneresorbedhere

Epiphysealplate

1

2

3

4

1

2

3

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APPOSITIONAL BONE GROWTH

• All bones widen and increase in diameter/thickness via appositional bone growth

• Sequence of events:

Osteoblasts in the osteogenic layer of the periosteum secrete new bone tissue onto the external surface of the bone

Osteoclasts in the endosteum slightly resorb bone tissue in the internal surface of the bone

Overall, more new bone tissue is added onto the external surface and old bone tissue is slightly resorbed from the internal surface resulting in a thicker but lighter bone.

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Hormonal Control of Postnatal Bone Growth

• Growth hormone – stimulates hepatocytes to produce Insulin-like growth factors ( IGFs)

• IGFs stimulate chondroblasts to produce hyaline cartilage on the epiphyseal faces of the epiphyseal plates and bone formation on the diaphyseal faces

• Sex steroid hormones ( testosterone in the male and the estrogens in the female) synergize with growth hormone to cause “growth spurt”

• Towards the end of adolescence, the sex steroid hormones antagonize the actions of growth hormone and the epiphyseal plates become ossified = EPIPHYSEAL PLATE CLOSURE – height determined

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Bone Remodeling• Adult bones constantly undergo bone formation on the periosteal

surface and bone resorption on the endosteal surface = Bone Remodeling

In healthy adults, the bone density remains constant because

• Rate of Bone formation = rate of bone resorption

• If the rate of resorption outpaces the rate of formation = OSTEOPOROSIS

• Functions of Bone Remodeling:

i) To maintain calcium homeostasis

ii) To allow for bone repair after fractures

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Normal and osteoporotic bone

Normal bone

Osteoporotic bone

www.mayoclinic.com/health/osteoporosis/DS00128

Page 32: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.11: Hormonal control of blood calcium levels, p. 189.

PTH;calcitoninsecreted

Calcitoninstimulatescalcium saltdepositin bone

Parathyroidglands releaseparathyroidhormone (PTH)

Thyroidgland

Thyroidgland

Parathyroidglands

Osteoclastsdegrade bonematrix and releaseCa2+ into blood

Falling bloodCa2+ levels

Rising bloodCa2+ levels

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

PTH

Imbalance

Imbalance

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Factors that Control Bone Remodeling• 2 factors: Hormonal control and mechanical stress

• Hormonal Control:Under hypercalcemic conditions, CALCITONIN is released to stimulate

osteoblasts to produce bone tissue and stimulate mineralization – uses calcium from blood

Under hypocalcemic conditions, PARATHYROID HORMONE (PTH) is released to stimulate osteoclasts to cause bone resorption to release calcium from bones into blood

I,25 dihydroxyvitamin D stimulates calcium absorption from the small intestine

• Mechanical Stress: Bones remodel/grow in response to mechanical stresses placed on the bones =

WOLFF’S LAW

Page 34: Skeletal system

Forms of evidence in support of Wolff’s Law

• Bone attachment sites for active skeletal muscles appear thicker – projections such as trochanters, spines,

• Bones of the upper limb often used are thicker than the less used limb – bones in the right arm of a right-handed individual are thicker than bones in the left arm and vice versa

• Long bones are thickest in the middle region of the diaphysis where bending stresses are greatest

• Bedridden individual not subjected to the stresses of walking or exercises lose bone density

• Astronauts who spend appreciably amount of time in space (where there’s no gravity and they cannot walk), lose bone density

Page 35: Skeletal system

Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn

Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.

Figure 6.12: Bone anatomy and stress, p. 190

Load here(body weight)

Head offemur

Compressionhere

Point ofno stress

Tensionhere