Bone TissueBone Tissue
Alam Zeb AmirAlam Zeb Amir
Identify main functions of osseous tissueIdentify main functions of osseous tissue
Identify the major parts of a longIdentify the major parts of a long
Describe the cells found in osseous tissueDescribe the cells found in osseous tissue
Describe the components of an osteonDescribe the components of an osteon
Compare and contrast intramembranousCompare and contrast intramembranous
and endochondral ossification.and endochondral ossification.
Osteology: study of osseous structures.Osteology: study of osseous structures.
Mineral homeostasisMineral homeostasis
Hemopoiesis: blood cell formationHemopoiesis: blood cell formation
Storage of adipose tissue: yellow marrowStorage of adipose tissue: yellow marrow
Long bone anatomyLong bone anatomy
Diaphysis: long shaft of boneDiaphysis: long shaft of bone
Epiphysis: ends of boneEpiphysis: ends of bone
Epiphyseal plate: growth plateEpiphyseal plate: growth plate
Metaphysis: b/w epiphysis and diaphysisMetaphysis: b/w epiphysis and diaphysis
Articular cartilage: covers epiphysisArticular cartilage: covers epiphysis
Periosteum: bone covering (pain sensitive)Periosteum: bone covering (pain sensitive)
Sharpey’s fibers: periosteum attaches toSharpey’s fibers: periosteum attaches to
underlying boneunderlying bone
Medullary cavity: Hollow chamber in boneMedullary cavity: Hollow chamber in bone
- red marrow produces blood cells- red marrow produces blood cells
- yellow marrow is adipose.- yellow marrow is adipose.
Endosteum: thin layer lining theEndosteum: thin layer lining the
medullary cavitymedullary cavity
Histology of bone tissueHistology of bone tissue
Cells are surrounded by matrix.Cells are surrounded by matrix.
- 25% water- 25% water
- 25% protein- 25% protein
- 50% mineral salts- 50% mineral salts
4 cell types make up osseous tissue4 cell types make up osseous tissue
Osteoprogenitor cellsOsteoprogenitor cells
Osteoprogenitor cells:Osteoprogenitor cells:
- derived from mesenchyme- derived from mesenchyme
- all connective tissue is derived- all connective tissue is derived
- unspecialized stem cells- unspecialized stem cells
- undergo mitosis and develop into- undergo mitosis and develop into
- found on inner surface of periosteum- found on inner surface of periosteum
and endosteum.and endosteum.
- bone forming cells- bone forming cells
- found on surface of bone- found on surface of bone
- no ability to mitotically divide- no ability to mitotically divide
- collagen secretors- collagen secretors
- mature bone cells- mature bone cells
- derived form osteoblasts- derived form osteoblasts
- do not secrete matrix material- do not secrete matrix material
- cellular duties include exchange of- cellular duties include exchange of nutrientsnutrients
and waste with blood.and waste with blood.
- bone resorbing cells- bone resorbing cells
- bone surface- bone surface
- growth, maintenance and bone repair- growth, maintenance and bone repair
Abundant inorganic mineral salts:Abundant inorganic mineral salts:
- Tricalcium phosphate in crystalline form called- Tricalcium phosphate in crystalline form called
- Calcium Carbonate: CaCOCalcium Carbonate: CaCO33
- Magnesium Hydroxide: Mg(OH)Magnesium Hydroxide: Mg(OH)22
- Fluoride and SulfateFluoride and Sulfate
These salts are deposited on the collagenThese salts are deposited on the collagen
fiber framework (tensile strength) andfiber framework (tensile strength) and
crystallization occurs.crystallization occurs.
- calcification or mineralization- calcification or mineralization
Compact bone: (Osteon) external layerCompact bone: (Osteon) external layer
- called lamellar bone (groups of- called lamellar bone (groups of
elongated tubules called lamella)elongated tubules called lamella)
- majority of all long bones- majority of all long bones
- protection and strength (wt. bearing)- protection and strength (wt. bearing)
- concentric ring structure- concentric ring structure
- blood vessels and nerves penetrate- blood vessels and nerves penetrate
periosteum through horizontalperiosteum through horizontal
openings called perforatingopenings called perforating (Volkmann’s)(Volkmann’s)
- central (Haversian) canals run- central (Haversian) canals run
longitudinally. Blood vessels andlongitudinally. Blood vessels and nerves.nerves.
- around canals are concentric lamella- around canals are concentric lamella
- osteocytes occupy lacunae (“little lakes”)- osteocytes occupy lacunae (“little lakes”)
which are between the lamellawhich are between the lamella
- radiating from the lacunea are channels- radiating from the lacunea are channels
called canaliculi. (finger like processescalled canaliculi. (finger like processes
of osteocytes)of osteocytes)
- Lacunae are connected to one another byLacunae are connected to one another by
- Osteon contains: - central canalOsteon contains: - central canal
- surrounding lamellae- surrounding lamellae
- lacunae- lacunae
- osteocytes- osteocytes
- canaliculi- canaliculi
Spongy bone (cancellous bone): internalSpongy bone (cancellous bone): internal
- latticework of bone tissue (haphazard- latticework of bone tissue (haphazard
- made of trabeculae (“little beams”)- made of trabeculae (“little beams”)
- filled with red and yellow bone marrow- filled with red and yellow bone marrow
- osteocytes get nutrients directly from- osteocytes get nutrients directly from
circulating blood.circulating blood.
- short, flat and irregular bone is made up- short, flat and irregular bone is made up
of mostly spongy boneof mostly spongy bone
Cancellous (spongy) boneCancellous (spongy) bone
Bone formation (ossification) occurs in two waysBone formation (ossification) occurs in two ways
1- Intramembranous ossification1- Intramembranous ossification
2- Endochondral ossification2- Endochondral ossification
Both methods above lead to the same boneBoth methods above lead to the same bone
formation but are different methods of gettingformation but are different methods of getting
Ossification (osteogenesis) begins around the 6Ossification (osteogenesis) begins around the 6thth
week of embryonic life. At this time the embryonicweek of embryonic life. At this time the embryonic
skeleton is made of fibrous membranes andskeleton is made of fibrous membranes and
hyaline cartilage.hyaline cartilage.
Hyaline Cartilage ReviewHyaline Cartilage Review
a. Most abundanta. Most abundant
b. Provides support, flexibility andb. Provides support, flexibility and
c. Located:c. Located:
a. forming nearly all the fetal skeletona. forming nearly all the fetal skeleton
b.b. articular cartilagearticular cartilage: ends of moving: ends of moving
c.c. costal cartilagecostal cartilage: ribs to sternum: ribs to sternum
d. tip of nosed. tip of nose
e. respiratory cartilagee. respiratory cartilage
Skeletal Cartilage:Skeletal Cartilage:
1.1. Chondrocytes: cartilage producingChondrocytes: cartilage producing cells.cells.
2. Lacunae: small cavities where the2. Lacunae: small cavities where the
chondrocytes are encased.chondrocytes are encased.
3. Extracellular matrix: jellylike ground3. Extracellular matrix: jellylike ground
4. Perichondrium: layer of dense4. Perichondrium: layer of dense
irregular connective tissue thatirregular connective tissue that surroundssurrounds
the cartilage.the cartilage.
5. No blood vessels or nerves5. No blood vessels or nerves
IntramembranousIntramembranous (within the membrane)(within the membrane)
ossification: Bone develops from a fibrousossification: Bone develops from a fibrous
- flat bones of skull- flat bones of skull
- mandible- mandible
- clavicles- clavicles
-mesenchymal cells become vascularized and-mesenchymal cells become vascularized and
become osteoprogenitor cells and thenbecome osteoprogenitor cells and then
- organic matrix of bone is secreted- organic matrix of bone is secreted
- osteocytes are formed- osteocytes are formed
- calcium and mineral salts are deposited and- calcium and mineral salts are deposited and
bone tissue hardens.bone tissue hardens.
- trabeculae develop and spongy bone is formed- trabeculae develop and spongy bone is formed
- red marrow fills spaces- red marrow fills spaces
Replacement of hyaline cartilage with bone is calledReplacement of hyaline cartilage with bone is called
.. Endochondral (intracartilaginous) ossificationEndochondral (intracartilaginous) ossification
Most bones are formed this way (i.e. long bones).Most bones are formed this way (i.e. long bones).
Where bone is going to form:Where bone is going to form:
1- mesenchymal cells differentiate into1- mesenchymal cells differentiate into
chondroblasts (immature cartilage cells) whichchondroblasts (immature cartilage cells) which
produces hyaline cartilage.produces hyaline cartilage.
Perichondrium develop around new cartilagePerichondrium develop around new cartilage
2- Chondrocytes (mature) mitotically divide increasing2- Chondrocytes (mature) mitotically divide increasing
in lengthin length
This pattern of growth:This pattern of growth: interstitial growth.interstitial growth.
Growth of cartilage inGrowth of cartilage in thicknessthickness occurs fromoccurs from
the deposition of new matrix to thethe deposition of new matrix to the
periphery formed by chondroblasts withinperiphery formed by chondroblasts within
the perichondrium.the perichondrium. Appositional growthAppositional growth..
Chondrocytes undergo hypertrophy, swellChondrocytes undergo hypertrophy, swell
and burst. pH of the matrix changes andand burst. pH of the matrix changes and
calcification is triggered. Ultimately,calcification is triggered. Ultimately,
cartilage cells die. Lacunae are nowcartilage cells die. Lacunae are now
Nutrients are supplied by way of the nutrientNutrients are supplied by way of the nutrient
artery passing through the perichondriumartery passing through the perichondrium
through the nutrient foramen.through the nutrient foramen.
Osteoprogenitor cells are stimulated in theOsteoprogenitor cells are stimulated in the
perichondrium to produce osteoblasts.perichondrium to produce osteoblasts.
A thin layer of compact bone is laid downA thin layer of compact bone is laid down
under the perichondrium called theunder the perichondrium called the
periosteal bone collar.periosteal bone collar.
Perichondrium becomes periosteumPerichondrium becomes periosteum
Osteoblasts begin to deposit bone matrixOsteoblasts begin to deposit bone matrix
forming spongy bone trabeculae.forming spongy bone trabeculae.
In the middle of the bone, osteoclasts breakIn the middle of the bone, osteoclasts break
down spongy bone trabeculae and form adown spongy bone trabeculae and form a
hollowed out cavity called the medullaryhollowed out cavity called the medullary
cavity. This cavity will be filled with redcavity. This cavity will be filled with red
bone marrow for hemopoiesis.bone marrow for hemopoiesis.
The shaft of the bone is replaced (wasThe shaft of the bone is replaced (was
hyaline cartilage) with compact bone.hyaline cartilage) with compact bone.
Physiology of bone growth:Physiology of bone growth:
- epiphyseal plate (bone length)- epiphyseal plate (bone length)
- 4 zones of bone growth under hGH.- 4 zones of bone growth under hGH.
1- Zone of resting cartilage:1- Zone of resting cartilage:
- no bone growth- no bone growth
- located near the epiphyseal plate- located near the epiphyseal plate
- scattered chondrocytes- scattered chondrocytes
- anchors plate to bone- anchors plate to bone
2- Zone of proliferating cartilage2- Zone of proliferating cartilage
- chondrocytes stacked like coins- chondrocytes stacked like coins
- chondrocytes divide- chondrocytes divide
3- Zone of hypertrophic (maturing) cartilage3- Zone of hypertrophic (maturing) cartilage
- large chondrocytes arranged in columns- large chondrocytes arranged in columns
- lengthwise expansion of epiphyseal plate- lengthwise expansion of epiphyseal plate
4- Zone of calcified cartilage4- Zone of calcified cartilage
- few cell layers thick- few cell layers thick
- occupied by osteoblasts and osteoclasts- occupied by osteoblasts and osteoclasts
and capillaries from the diaphysisand capillaries from the diaphysis
- cells lay down bone- cells lay down bone
- dead chondrocytes surrounded by a calcified- dead chondrocytes surrounded by a calcified
matrix. Matrix resembles long spicules ofmatrix. Matrix resembles long spicules of calcifiedcalcified
cartilage. Spicules are partly eroded bycartilage. Spicules are partly eroded by osteoclastsosteoclasts
and then covered in bone matrixand then covered in bone matrix from osteoblasts:from osteoblasts:
spongy bone is formed.spongy bone is formed.
Age 18-21: Longitudinal bone growth ends whenAge 18-21: Longitudinal bone growth ends when
epiphysis fuses with the diaphysis.epiphysis fuses with the diaphysis.
- epiphyseal plate closure- epiphyseal plate closure
- epiphyseal line is remnant of this- epiphyseal line is remnant of this
- last bone to stop growing: clavicle- last bone to stop growing: clavicle
Bone width: increase in diameter of boneBone width: increase in diameter of bone
occurs through appositional growth .occurs through appositional growth .
- Osteoblasts located beneath the- Osteoblasts located beneath the
periosteum secrete bone matrix and buildperiosteum secrete bone matrix and build
bone on the surfacebone on the surface
- Osteoclasts located in the endosteum- Osteoclasts located in the endosteum
resorbs (breakdown) bone.resorbs (breakdown) bone.
Bone Remodeling:Bone Remodeling:
- bone continually renews itself- bone continually renews itself
- never metabolically at rest- never metabolically at rest
- enables Ca to be pulled from bone when- enables Ca to be pulled from bone when
blood levels are lowblood levels are low
- osteoclasts are responsible for matrix- osteoclasts are responsible for matrix
- produce lysosomal enzymes and acids- produce lysosomal enzymes and acids
- spongy bone replaced every 3-4 years- spongy bone replaced every 3-4 years
- compact bone every 10 years- compact bone every 10 years
- Blood calcium levels signal release of either- Blood calcium levels signal release of either
parathyroid hormoneparathyroid hormone (PTH, secreted by(PTH, secreted by
parathyroid gland) andparathyroid gland) and calcitonincalcitonin (secreted(secreted
by thyroid).by thyroid).
PTH causes calcium release from bone matrixPTH causes calcium release from bone matrix
byby stimulating osteoclast activity and bonestimulating osteoclast activity and bone
Calcitonin inhibits bone resorption and causesCalcitonin inhibits bone resorption and causes
calcium salts to be deposited in bone matrix.calcium salts to be deposited in bone matrix.
Vitamins A, C, D and BVitamins A, C, D and B1212 help in bone remodelinghelp in bone remodeling
Fractures: Any bone break.Fractures: Any bone break.
- blood clot will form around break- blood clot will form around break
- fracture hematoma- fracture hematoma
- inflammatory process begins- inflammatory process begins
- blood capillaries grow into clot- blood capillaries grow into clot
- phagocytes and osteoclasts remove- phagocytes and osteoclasts remove
damaged tissuedamaged tissue
- procallus forms and is invaded by- procallus forms and is invaded by
osteoprogenitor cells and fibroblastsosteoprogenitor cells and fibroblasts
- collagen and fibrocartilage turns- collagen and fibrocartilage turns
procallus to fibrocartilagenous (soft) callusprocallus to fibrocartilagenous (soft) callus
- broken ends of bone are bridged by callusbroken ends of bone are bridged by callus
- Osteoprogenitor cells are replaced byOsteoprogenitor cells are replaced by
osteoblasts and spongy bone is formedosteoblasts and spongy bone is formed
- bony (hard) callus is formedbony (hard) callus is formed
- callus is resorbed by osteoclasts and compactcallus is resorbed by osteoclasts and compact
bone replaces spongy bone.bone replaces spongy bone.
Remodeling : the shaft is reconstructed toRemodeling : the shaft is reconstructed to
resemble original unbroken bone.resemble original unbroken bone.
Closed reduction - bone ends coaxed back intoClosed reduction - bone ends coaxed back into
place by manipulationplace by manipulation
Open reduction - surgery, bone ends securedOpen reduction - surgery, bone ends secured
together with pins or wirestogether with pins or wires
Simple/Closed: bone breaks cleanly, butSimple/Closed: bone breaks cleanly, but
doesdoes not penetrate skinnot penetrate skin
Compound/Open: broken ends of boneCompound/Open: broken ends of bone
protrude through tissue and skinprotrude through tissue and skin
Comminuted bone fragments into manyComminuted bone fragments into many
Compression: bone is crushed ( due toCompression: bone is crushed ( due to
porous bone)porous bone)
Depressed: broken bone is pressed inwardDepressed: broken bone is pressed inward
(e.g. in skull)(e.g. in skull)
Colles’: posterior displacement of distal endColles’: posterior displacement of distal end
Smith’s: anterior displacement of distalSmith’s: anterior displacement of distal endend
of radius (flexion)of radius (flexion)
Transverse: break occurs across the longTransverse: break occurs across the long axisaxis
of a boneof a bone
Impacted: broken bone ends are forcedImpacted: broken bone ends are forced intointo
each othereach other
Spiral: ragged break as a result ofSpiral: ragged break as a result of
excessive twisting of boneexcessive twisting of bone
Epiphyseal: break occurring alongEpiphyseal: break occurring along
epiphyseal line/plateepiphyseal line/plate
Greenstick: bone breaks incompletelyGreenstick: bone breaks incompletely
Pott's: malleolus of tibia and fibula breakPott's: malleolus of tibia and fibula break