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
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)
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)
2 Types of Bone Tissue
Spongy bone
Compact bone
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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.
The Embryonic Skeleton
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
34
5
• 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
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
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
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
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
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
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.
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
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
Normal and osteoporotic bone
Normal bone
Osteoporotic bone
www.mayoclinic.com/health/osteoporosis/DS00128
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
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
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
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