Bone TissueBone Tissue

Ch. 6Ch. 6

Objectives:Objectives: Identify main functions of osseous Identify main functions of osseous

tissuetissue Identify the major parts of a longIdentify the major parts of a long Describe the cells found in osseous Describe the cells found in osseous

tissuetissue Describe the components of an osteonDescribe the components of an osteon Compare and contrast Compare and contrast

intramembranous and endochondral intramembranous and endochondral ossification.ossification.

Osteology: study of osseous Osteology: study of osseous structures.structures.

SupportSupport

ProtectionProtection

MovementMovement

Mineral homeostasisMineral homeostasis

Hemopoiesis: blood cell formationHemopoiesis: blood cell formation

Storage of adipose tissue: yellow Storage of adipose tissue: yellow marrow 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 to Sharpey’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 the Endosteum: thin layer lining the medullary cavitymedullary cavity

Long boneLong bone

DiaphysisDiaphysis

EpiphysisEpiphysis

MetaphysisMetaphysis

Epiphyseal (growth) plateEpiphyseal (growth) plate

Medullary cavityMedullary cavity

Histology of bone tissueHistology of bone tissueCells 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 tissueOsteoprogenitor cellsOsteoprogenitor cellsOsteoblastsOsteoblastsOsteocytesOsteocytesOsteoclastsOsteoclasts

Osteoprogenitor cells:Osteoprogenitor cells:

- derived from mesenchyme- derived from mesenchyme

- all connective tissue is - all connective tissue is derivedderived

- unspecialized stem cells- unspecialized stem cells

- undergo mitosis and develop - undergo mitosis and develop into into osteoblasts osteoblasts

- found on inner surface of - found on inner surface of periosteum periosteum and endosteum. and endosteum.

Osteoblasts:Osteoblasts:- 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

Osteocytes: Osteocytes: - 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 nutrients and waste with blood. nutrients and waste with blood.

OsteocyteOsteocyte

OsteoclastsOsteoclasts- 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 - Tricalcium phosphate in crystalline form

called hydroxyapatitecalled hydroxyapatite

CaCa33(PO(PO44))22(OH)(OH)22

- 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 These salts are deposited on the collagen fiber framework (tensile collagen fiber framework (tensile strength) and crystallization occurs.strength) and crystallization occurs.

- calcification or mineralization- calcification or mineralization

Compact bone: (Osteon) external Compact bone: (Osteon) external layerlayer

- 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. - protection and strength (wt. bearing)bearing)

- concentric ring structure- concentric ring structure

- blood vessels and nerves penetrate - blood vessels and nerves penetrate periosteum through horizontal periosteum through horizontal openings called perforating openings called perforating

(Volkmann’s) canals.(Volkmann’s) canals.

- central (Haversian) canals run - central (Haversian) canals run longitudinally. Blood vessels and longitudinally. Blood vessels and nerves.nerves.

- around canals are concentric - around canals are concentric lamellalamella

- osteocytes occupy lacunae (“little - osteocytes occupy lacunae (“little lakes”) lakes”) which are between the which are between the lamellalamella

- radiating from the lacunea are - radiating from the lacunea are channels channels called canaliculi. (finger called canaliculi. (finger like processes like processes of osteocytes)of osteocytes)

- Lacunae are connected to one Lacunae are connected to one another by canaliculi.another by canaliculi.

- Osteon contains: - central canalOsteon contains: - central canal

- surrounding - surrounding lamellaelamellae

- lacunae- lacunae

- osteocytes- osteocytes

- canaliculi- canaliculi

Compact boneCompact bone

Spongy bone (cancellous bone): internal Spongy bone (cancellous bone): internal layerlayer

- latticework of bone tissue (haphazard - latticework of bone tissue (haphazard arrangement).arrangement).

- 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 - short, flat and irregular bone is made up up of mostly spongy boneof mostly spongy bone

Cancellous (spongy) boneCancellous (spongy) bone

Bone formation (ossification) occurs in two Bone formation (ossification) occurs in two waysways1- Intramembranous ossification1- Intramembranous ossification2- Endochondral ossification2- Endochondral ossification

Both methods above lead to the same bone Both methods above lead to the same bone

formation but are different methods of formation but are different methods of getting there.getting there.

Ossification (osteogenesis) begins around Ossification (osteogenesis) begins around the 6the 6thth -7 -7thth week of embryonic life. At this week of embryonic life. At this time the embryonic skeleton is made of time the embryonic skeleton is made of fibrous membranes and hyaline cartilage.fibrous membranes and hyaline cartilage.

Hyaline Cartilage ReviewHyaline Cartilage Reviewa. Most abundanta. Most abundantb. Provides support, flexibility and b. Provides support, flexibility and resilience resiliencec.   Located:c.   Located:

a. forming nearly all the fetal a. forming nearly all the fetal skeletonskeleton

b. b. articular cartilagearticular cartilage: ends of : ends of moving moving bones bones

c. c. costal cartilagecostal cartilage: ribs to : ribs to sternumsternum

d. tip of nosed. tip of nose e. respiratory cartilagee. respiratory cartilage

Skeletal Cartilage:Skeletal Cartilage:

1. 1. Chondrocytes: cartilage Chondrocytes: cartilage producing producing cells.cells.

2.      Lacunae: small cavities where 2.      Lacunae: small cavities where the the chondrocytes are encased.chondrocytes are encased.

3.      Extracellular matrix: jellylike 3.      Extracellular matrix: jellylike ground ground substance.substance.

4.      Perichondrium: layer of dense 4.      Perichondrium: layer of dense irregular connective tissue that irregular connective tissue that surrounds the cartilage.surrounds the cartilage.

5.      No blood vessels or nerves5.      No blood vessels or nerves

IntramembranousIntramembranous (within the (within the membrane) ossification: Bone develops membrane) ossification: Bone develops from a fibrous membrane.from a fibrous membrane.

- flat bones of skull- flat bones of skull- mandible- mandible- clavicles- clavicles

-mesenchymal cells become vascularized -mesenchymal cells become vascularized and and become osteoprogenitor cells and become osteoprogenitor cells and then then osteoblasts.osteoblasts.- organic matrix of bone is secreted- organic matrix of bone is secreted- osteocytes are formed- osteocytes are formed- calcium and mineral salts are deposited - calcium and mineral salts are deposited and and bone tissue hardens.bone tissue hardens.- trabeculae develop and spongy bone is - trabeculae develop and spongy bone is formedformed- 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) ossification Endochondral (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 into 1- mesenchymal cells differentiate into chondroblasts (immature cartilage cells) which chondroblasts (immature cartilage cells) which produces hyaline cartilage.produces hyaline cartilage.

Perichondrium develop around new cartilagePerichondrium develop around new cartilage

2- Chondrocytes (mature) mitotically divide 2- Chondrocytes (mature) mitotically divide increasing in lengthincreasing in length

This pattern of growth: This pattern of growth: interstitial growth.interstitial growth.

- growth from within- growth from within

Growth of cartilage inGrowth of cartilage in thickness thickness occurs occurs from the deposition of new matrix to from the deposition of new matrix to the periphery formed by the periphery formed by chondroblasts within the chondroblasts within the perichondrium. perichondrium. Appositional growthAppositional growth..

Chondrocytes undergo hypertrophy, Chondrocytes undergo hypertrophy, swell and burst. pH of the matrix swell and burst. pH of the matrix changes and calcification is changes and calcification is triggered. Ultimately, cartilage cells triggered. Ultimately, cartilage cells die. Lacunae are now empty.die. Lacunae are now empty.

Nutrients are supplied by way of the Nutrients are supplied by way of the nutrient artery passing through the nutrient artery passing through the perichondrium through the nutrient perichondrium through the nutrient foramen.foramen.

Osteoprogenitor cells are stimulated in Osteoprogenitor cells are stimulated in the perichondrium to produce the perichondrium to produce osteoblasts.osteoblasts.

A thin layer of compact bone is laid A thin layer of compact bone is laid down under the perichondrium called down under the perichondrium called the periosteal bone collar.the periosteal bone collar.

Perichondrium becomes periosteumPerichondrium becomes periosteum

Osteoblasts begin to deposit bone Osteoblasts begin to deposit bone matrix forming spongy bone matrix forming spongy bone trabeculae.trabeculae.

In the middle of the bone, osteoclasts In the middle of the bone, osteoclasts break down spongy bone trabeculae break down spongy bone trabeculae and form a hollowed out cavity called and form a hollowed out cavity called the medullary cavity. This cavity will the medullary cavity. This cavity will be filled with red bone marrow for be filled with red bone marrow for hemopoiesis. hemopoiesis.

The shaft of the bone is replaced (was The 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 - 4 zones of bone growth under hGH.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 - dead chondrocytes surrounded by a calcified calcified matrix. Matrix resembles long matrix. Matrix resembles long spicules of spicules of calcified cartilage. Spicules calcified cartilage. Spicules are partly eroded by are partly eroded by osteoclasts and osteoclasts and then covered in bone matrix then covered in bone matrix from from osteoblasts: spongy bone is formed.osteoblasts: spongy bone is formed.

Age 18-21: Longitudinal bone growth ends Age 18-21: Longitudinal bone growth ends when epiphysis fuses with the diaphysis.when 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 Bone width: increase in diameter of bone occurs through appositional bone occurs through appositional growth .growth .

- Osteoblasts located beneath the - Osteoblasts located beneath the periosteum secrete bone matrix and periosteum secrete bone matrix and build bone on the surfacebuild bone on the surface

- Osteoclasts located in the - Osteoclasts located in the endosteum resorbs (breakdown) endosteum resorbs (breakdown) bone.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 - enables Ca to be pulled from bone when when blood levels are lowblood levels are low

- osteoclasts are responsible for - osteoclasts are responsible for matrix matrix destructiondestruction

- produce lysosomal enzymes and - produce lysosomal enzymes and acidsacids

- spongy bone replaced every 3-4 - spongy bone replaced every 3-4 yearsyears

- 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 (PTH, secreted

by by parathyroid gland) and parathyroid gland) and calcitonincalcitonin (secreted (secreted by thyroid). by thyroid).

PTH causes calcium release from bone PTH causes calcium release from bone matrix by matrix by stimulating osteoclast activity and stimulating osteoclast activity and bone bone resorption.resorption.

Calcitonin inhibits bone resorption and Calcitonin inhibits bone resorption and causes causes calcium salts to be deposited in calcium salts to be deposited in bone matrix. bone matrix.

Vitamins A, C, D and BVitamins A, C, D and B12 12 help in bone help in bone remodelingremodeling

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) procallus to fibrocartilagenous (soft) calluscallus

- broken ends of bone are bridged by callusbroken ends of bone are bridged by callus- Osteoprogenitor cells are replaced by Osteoprogenitor 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 callus is resorbed by osteoclasts and

compact compact bone replaces spongy bone.bone replaces spongy bone.Remodeling : the shaft is reconstructed to Remodeling : the shaft is reconstructed to resemble original unbroken bone. resemble original unbroken bone.

Closed reduction - bone ends coaxed back Closed reduction - bone ends coaxed back

into place by manipulationinto place by manipulation

Open reduction - surgery, bone ends Open reduction - surgery, bone ends secured together with pins or wiressecured together with pins or wires

Simple/Closed: bone breaks cleanly, but Simple/Closed: bone breaks cleanly, but does does not penetrate skin not penetrate skin

Compound/Open: broken ends of bone Compound/Open: broken ends of bone protrude through tissue and skin protrude through tissue and skin

Comminuted bone fragments into many Comminuted bone fragments into many pieces pieces

Compression: bone is crushed ( due to Compression: bone is crushed ( due to porous bone) porous bone)

Depressed: broken bone is pressed Depressed: broken bone is pressed inward inward (e.g. in skull) (e.g. in skull)

Colles’: posterior displacement of distal Colles’: posterior displacement of distal end end of radius (extension)of radius (extension)

Smith’s: anterior displacement of distal Smith’s: anterior displacement of distal end of radius (flexion)end of radius (flexion)

Transverse: break occurs across the Transverse: break occurs across the long long axis of a bone axis of a bone

Impacted: broken bone ends are forced Impacted: broken bone ends are forced into each other into each other

Spiral: ragged break as a result of Spiral: ragged break as a result of excessive twisting of bone excessive twisting of bone

Epiphyseal: break occurring along Epiphyseal: break occurring along epiphyseal line/plate epiphyseal line/plate

Greenstick: bone breaks incompletely Greenstick: bone breaks incompletely Pott's: malleolus of tibia and fibula Pott's: malleolus of tibia and fibula

breakbreak

GaleazziGaleazzi Fx. Fx.

Monteggia Monteggia

Pott’s FxPott’s Fx

Colles’ Fx.Colles’ Fx.