MECH2901)–!SEMESTER&2"
Skeletal'System'–'Bones'&'Bone'Tissue:'[7%10"years"you"have"a"new"skeleton]'
The$skeleton$apparatus$is$essential$for$vertebrate$life;$it$ensures$mechanical$support,$defence$and$provides$a$
mineral$reservoir$
Describe'the'primary'functions'of'the'skeletal'system.''
1.
Support'
Bone"is"hard"and"rigid;"cartilage"is"flexible"yet"strong."Cartilage"in"nose,"external"
ear,"thoracic"cage"and"trachea."Ligaments%"bone"to"bone!
2.
Storage'of'Minerals'(Ca'and'P)'
Fat"stored"in"marrow"cavities!
3.
Blood'cell'production'(red'
marrow)'
Bone"provides"a"niche"for"bone"marrow"that"gives"rise"to"blood"cells"and"
platelets!
4.
Protection'
Skull"around"brain;"ribs,"sternum,"vertebrae"protect"organs"of"thoracic"cavity!
5.
Movement'
Produced"by"muscles"on"bones,"via"tendons."Ligaments"allow"some"movement"
between"bones"but"prevent"excessive"movemen!
6.
Absorb'Shock'
Impacts"during"motion"need"to"be"absorbed"to"reduce"strain"on"bone"and"joints"
and"damage"to"soft"tissues!
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STRUCTURE'OF'LONG'BONES:'
Structure'
Description'
Diaphysis''
•
The"shaft"
•
Compact"bone"(or"dense"bone)"
•
A"central"space"called"medullary"(marrow)"cavity:""
Epiphysis''
o
Cavity"is"Red"marrow"in"children"
o
Changes"to"Yellow"in"limb"bones"&"skull"
(except"for"epiphyses"of"long"bones)"
•
End"of"Bone"
•
Mostly"spongy"(cancellous)"bone"
Metaphysis'
•
Where"diaphysis"and"epiphysis"meet"
Epiphyseal'Plate'
(growth'plate)'
•
Hyaline"cartilage"present"until"growth"stops"
Epiphyseal'Line'
•
Bond"stops"grown"in"length"
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Bone is a cellular and vascular structure
continually being renewed and repaired
Compare'the'structures'and'functions'of'compact'bone'and'spongy'bone.''
COMPACT'(corticol)'BONE"
Osteons'(Haversian'systems)''
•
Blood"vessel%filled"central"(or"Haversian)"canals:"
parallel"to"long"axis""
•
Concentric'lamellae"of"bone"surround"central"
canal""
•
Circumferential'lamellae"on"the"periphery"of"a"
bone""
•
Interstitial'lamellae"between"osteons."
Remnants"of"osteons"replaced"through"
remodeling""
•
Lacunae"and"canaliculi"contain"osteocytes"and"
fluid""
Perforating'or'Volkmann’s'canal'
•
perpendicular"to"long"axis."Both"perforating"
and"central"canals"contain"blood"vessels.""
•
Direct"flow"of"nutrients"and"signals"from"
vessels"through"cell"processes"of"osteocytes"
and"from"one"cell"to"the"next."""
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SPONGY'(Cancellous)'BONE'
• No"osteons"""
• Trabeculae:"interconnecting"rods"or"plates"of"
bone."Like"scaffolding""
o
The"space"between"trabeculae"is"filled"
with"red'bone'marrow""
o Covered"with"endosteum"""
o Oriented"along"stress"lines"""
• Holds'Yellow'bone'marrow""(yellow"="stores"fat)"
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Bone'Composition'
Bone"is"a"composite"material"with"2"phases:"""
1)
Organic:"collagen"type"I,"proteoglycans"and"other"proteins""
2)
Inorganic:"hydroxyapatite%like"mineral"phase."CaPO4
"
crystals"with"frequent"substitutions"of"carbonate"and"other"
anions"and"cations;"more"accurately"called"carbonate"
apatite"""
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'
Identify'the'cell'types'in'bone,'and'list'their'major'functions''
Component'
Description'
Collagen'Type'1'
•
1
Lacunae'
•
Spaces"occupied"by"osteocyte"cell"body"
Canaliculi'
•
Canals"occupied"by"osteocyte"cell"processes"that"connect"to"adjacent"osteocytes"and"bone"
surfaces"
•
Nutrients"diffuse"through"tiny"amount"of"liquid"surrounding"cell"and"filling"lacunae"and"
canaliculi."""
•
Form"from"osteoblasts"that"become"surrounded"by"bone"matrix"""
Woven'Bone'
•
Collagen"fibers"randomly"oriented""
(Bad'quality'
produced'quickly)'
•
Formed"VERY'QUICKLY'during:"
/3'of'bone'is'made'of'protein'matrix"(80% is collagen type 1, 20% - other proteins [i.e.
signaling proteins released during remodelling of bone and proteins that direct and maintain the
mineralisation of bone]
1.
fetal"development"
2.
fracture"repair"(before"being"remodeled"to"become"lamellar"bone)"
Lamellar'Bone'
•
Woven"bone"is"REMODELLED'into"lamellar"bone"[i.e."remove"old"bone"%%>"add"new"bone]"
(Better'quality)'
•
Mature"bone"in"sheets"called"lamelae"
•
Alternating"thick"and"thin"collagen"sheets"with"fibrils"and"mineral"crystals"in"different"
orientations"in"different"layers"(for"strength)"in"a"plywood%like"structure""
•
FORMED'SLOWLY:"Fibers"are"oriented"in"one"direction"in"each"layer,"but"in"different"
directions"in"different"layers"for"strength""
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Bone'Cells:.''
Cell'Type'
Description'
Osteocytes((
•
[sense(bone(
strain(and(
damage](
Derived"from"haematopoietic"stem"cells"which"become"monocytes"[Do"not"divide]"
2"major"functions:(
1.
To"maintain"protein"and"mineral"content"of"surrounding"matrix"""
2.
Repairs(damaged(bone(by(sense(strain(and(bone(microdamage((through(canaliculi(fluid(
flow((signals)(!(Induces(Bone(Resorption(or(Bone(Remodelling(or(Bone(Formation "
•
Mature"bone"cells"that"maintain"the"bone"matrix""(
•
Live"in"lacunae"within"bone"matrix""(
•
Connect"by"cytoplasmic"extensions"through"canaliculi"through"the"matrix"""(
Osteoblasts(
•
[Makes(new(
Bone](
Derived$from$mesenchymal$stem$cells$!$dense$connective$tissue$(adipocytes,$myoctyes,$
chondroblasts,$osteoblasts)$
•
"Immature"bone"cells"that"secrete"matrix"compounds"(osteogenesis)"$
•
Osteoid"—"matrix"produced"by"osteoblasts,"but"not"yet"calcified"to"form"bone"$
•
Derived$from$monocytes$from$haematopoietic$stem$cells$which$produce$macrophages"
Osteoclasts(
•
[Removes(Bone($
<$secreting$acid$ •
and$protein$
•
digesting$
•
enzymes](
•
Giant,"multinucleate"cells"–"Dissolve"bone"matrix"and"release"stored"minerals"(osteolysis)""
Sealing'zone:"Donut"shape"seal"to"create"a"pocket"against"the"bone"surface"""
Ruffled'border:"where"cell"membrane"borders"bone"where"resorption"is"taking"place.""
"
+
H ions"pumped"across"membrane,"acid"formed"demineralizes"bone."""
Release"enzymes"that"digest"the"bone"protein"matrix."""
Osteoblasts'and'woven'bone'formation''
1.
Collagen"and"other"matrix"proteins"produced"by"Endoplasmic"Reticulum"and"golgi.""
2.
Secreted"rapidly"and"deposited"in"a"disorganised"manner"on"the"bone"surface."""
3.
Matrix"mineralised"by"uncontrolled"deposition"of"Ca"and"P"delivered"in"matrix"
vesicles."""
4.
Osteoblasts"surrounded"by"bone"(matrix)"become"osteocytes"
Osteoblasts'and'Lamellar'bone'formation''
1.
Formation"of"bone"through"ossification"or"osteogenesis."Collagen"and"other"matrix"
proteins"produced"by"Endoplasmic"Reticulum"and"golgi.""
2.
Secreted"and"deposited"in"highly'ordered"lamellar"structure"on"bone"surface.""
3.
Matrix"matured"for"about'15'days"then"mineralised"by"controlled"deposition"of"Ca"
and"P."
4.
Occasional"osteoblasts"become"surrounded"by"matrix"and"become"osteocytes"
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Harversian'Remodelling'of'Cortical'Bone'
1.
Osteoclasts"form"a"cutting"cone"and"tunnel"through"the"bone"forming"a"tunnel.""
2.
Blood"vessels"advance"with"the"osteoclasts.""
3.
Osteoblasts"then"form"and"lay"concentric"layers"of"bone"matrix"until"the"tunnel"is"almost"completely"filled.""
4.
This"gives"rise"to"Haversian"systems"seen"in"cross"section"as"circular"structures"surrounding"blood"vessels"
with"bone"formed"in"concentric"lamellae""
"
Osteoblasts(balance(many(stimuli(to(regulate(both(bone(resorption(and(bone(formation((
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Calcium'Homeostasis""
•
Bone"is"major"storage"site"for"Ca"""
•
Ca"levels"in"blood"dependent"on"Ca"movement"into"or"out"of"bone.""
•
Calcium"enters"bone"when"osteoblasts"create"new"bone;"calcium"leaves"bone"when"osteoclasts"break"
down"bone"""
•
2"hormones"control"blood"calcium"levels"%"parathyroid'hormone"and"calcitonin"
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Osteoprotegerin (OPG) Acts to Oppose the Stimulation of Osteoclast
Differentiation and Activation by RANK Ligand (RANKL) which
Mediates the Resorptive Actions of Hormones and Cytokines
Amount of Bone Resorption Depends on the
Balance of RANK Ligand and OPG
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