Lecture Cartilage and Bone 2009

7/30/2019 Lecture Cartilage and Bone 2009

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Histology Department

Medical Faculty

University of Sumatera Utara

Lecture : Histology of

Cartilage and Bone


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CARTILAGE

Early Fetal Life: Forms most of the skeleton

Persists in adults over the

articular surfaces of bones Sole skeletal support in the

respiratory passage and

parts of the ear


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Collagenous Fibers for increase in the tensile

strength

Elastic Fibers

different regions of for elasticity

MATRIX contains:

Adapt the tissue

to

the mechanical

requirements of

the

different

regions ofthe body

without

permanent

distortion


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MESENCHYME surrounding the enlarging mass of cartilage iscompressed and forms a fibrous envelope the PERICHONDRIUM.


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TWO PROCESSES BY WHICH

CARTILAGE GROWS:

1. Interstitial or ENDOGENOUS

1. Expansion of cartilage from within

2. Results from mitotic division of pre

existing chondrocytes2. Appositional or EXOGENOUS

1. addition of new layers of cartilage to

one surface

2. results from differentiation within theinner layer of PERICHONDRIUM


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CartilageA. Contains water, but no nerves, vascular & lymph

vessels

B. There are 3 basic types.

1. Hyaline - smooth, glassy, highly collagenica.articular - jointsb. costal - ribsc. respiratoryd. laryngeal - larynxe. nasal

2. Elastica. external earb. epiglottis

3. Fibrocartilagea. intervertebral discsb. knee joints

Note: The differences in the KIND and ABUNDANCE OFFIBERS incorporated within the matrix form the basis of

classification


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HYALINE CARTILAGE

appears as a translucent, bluish-white

mass in fresh conditions

forms the articular surfaces to bone within

joints, the costal cartilages,and the

cartilages of the nose, larynx, trachea, and

the bronchi

in the fetus, nearly all the skeleton is first

laid down as HYALINE cartilage, which is

replaced later by bone.


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ELASTIC CARTILAGE

fresh elastic cartilage has a yellowish color owing to thepresence of elastin in the elastic fibers

found in the external ear, the walls of the externalauditory canals, the eustachian tubes, the epiglottis, andthe cuneiform cartilage in the larynx.

Elastic cartilage is essentially identical to hyalinecartilage except that it contains an ABUNDANT

NETWORK OF FINE ELASTIC FIBERS in addition to thecollagen fibers.

frequently found to be gradually continuous with hyalinecartilage

Like hyaline cartilage possesses a perichondrium.


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FIBROCARTILAGE

transitional form between cartilageand dense connective tissue

occurs where a tough support or

tensile strength is required found in the intervertebral disc of

certain other joints

NEVER occurs alone, but merges

gradually into neighboring hyalinecartilage or with dense fibroustissue.

Lacks a perichondrium.


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REGENERATION OF

CARTILAGE TISSUE

Except in young children damagedcartilage regenerates withdifficulty and often incompletely.

It is by an activity of theperichondrium which invades theinjured area and generates newcartilage.

In extensively damaged areas andoccasionally in small areas, theperichondrium produces a scar ofDENSE CONNECTIVE TISSUEinstead of forming a NEW

CARTILAGE


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Bone as a Tissue

Connective tissue with a matrix

hardened by minerals (calcium

phosphate)

Individual bones consist of bone

tissue, marrow, blood, cartilage

and periosteum

Continually remodels itself Functions of the skeletal system

support, protection, movement,

electrolyte balances, acid-base

balance and blood formation


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65% inorganic (Ca)

35% organic

(34% collagen, ..)

(1% cells)


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Shapes of Bones

Long bones levers

acted upon by muscles

Short bones glideacross one another in

multiple directions

Flat bones protect soft

organs

G l F t f


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General Features of

Bones

Shaft (diaphysis) = cylinder of compact bone marrow cavity (medullary cavity) lined with

endosteum (osteogenic cells and reticular

connective tissue) Enlarged ends (epiphyses)

spongy bone covered by compact bone

enlarged to strengthen joint and attach ligaments

Joint surface covered with articular cartilage Shaft covered with periosteum

outer fibrous layer of collagen

inner osteogenic layer of bone forming cells

Epiphyseal plate (growth plate)

St t f


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Structure of a

Long Bone

Compact and

spongy bone

Marrow cavity

Articular cartilage

Periosteum

St t f Fl t


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Structure of a Flat

Bone External and

internal surfacescomposed of

compact bone

Middle layer isspongy bone and

bone marrow

Skull fracture may

leave inner layer ofcompact bone

unharmed


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Bone cells

C ll f O


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Cells of Osseous

Tissue (1)

Osteogenic cells in endosteum, periosteum or central canals

give rise to new osteoblasts

arise from embryonic fibroblasts

multiply continuously

Osteoblasts mineralize organic matter of matrix

Osteocytes are osteoblasts trapped in the matrix they formed

cells in lacunae connected by gap junctions inside canaliculi

C ll f O


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Cells of Osseous

Tissue (2)

Osteoclasts develop in bone marrow by fusion of 3-

50 stem cells

Reside in pits that they ate into the bone

M t i f O


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Matrix of Osseous

Tissue Dry weight = 1/3 organic and 2/3

inorganic matter Organic matter

collagen, glycosaminoglycans,proteoglycans and glycoproteins

Inorganic matter 85% hydroxyapatite

10% calcium carbonate

other minerals (fluoride, potassium,magnesium)

Combination provides for strength andresilience minerals resist compression; collagen

resists tension

bone adapts by varying proportions

Hi t l f C t


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Histology of Compact

Bone


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Compact Bone

Osteon = basic structural unit cylinders formed from layers (lamellae)

of matrix around central canal

(osteonic canal) collagen fibers alternate between right- and

left-handed helices from lamella to lamella

osteocytes connected to each otherand their blood supply by tiny cell

processes in canaliculi Perforating canals or Volkmanncanals vascular canals perpendicularly joining

central canals


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Blood Vessels of Bone


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Spongy Bone

Spongelike appearance formed by

plates of bone called trabeculae

spaces filled with red bone marrow

Trabeculae have few osteons or central

canals

no osteocyte is far from blood of bone

marrow

Provides strength with little weight

trabeculae develop along bones lines of

stress

S B St t


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Spongy Bone Structure

and Stress


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Bone Marrow

In medullary cavity (long bone) and

among trabeculae (spongy bone)

Red marrow like thick blood

reticular fibers and immature cells

Hemopoietic (produces blood cells)

in vertebrae, ribs, sternum, pelvic

girdle and proximal heads of femur

and humerus in adults

Yellow marrow

fatty marrow of long bones in adults

Gelatinous marrow of old age

yellow marrow replaced with reddish

jelly

Intramembranous


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Intramembranous

Ossification

Condensation of mesenchyme intotrabeculae

Osteoblasts on trabeculae lay down

osteoid tissue (uncalcified bone) Calcium phosphate is deposited in the

matrix forming bony trabeculae ofspongy bone

Osteoclasts create marrow cavity Osteoblasts form compact bone at

surface

Surface mesenchyme produces

periosteum

Intramembranous


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Intramembranous

Ossification 1

Produces flat bones of skull and clavicle.

Intramembranous


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Intramembranous

Ossification 2

Note the periosteum and osteoblasts.

Stages of Endochondral


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Stages of Endochondral

Ossification

Endochondral


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Endochondral

Ossification 1

Bone develops from pre-existingmodel perichondrium and hyaline cartilage

Most bones develop this process Formation of primary ossificationcenter and marrow cavity in shaft ofmodel

bony collar developed by osteoblasts chondrocytes swell and die

stem cells give rise to osteoblasts andclasts

bone laid down and marrow cavitycreated

Primary Ossification Center


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Primary Ossification Center

and Primary Marrow Cavity

Endochondral


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Secondary ossification centers andmarrow cavities form in ends ofbone

same process

Cartilage remains as articularcartilage and epiphyseal (growth)plates

growth plates provide for increase inlength of bone during childhood andadolescence

by early twenties, growth plates aregone and primary and secondarymarrow cavities united

Endochondral

Ossification 2

S d O ifi ti C t


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Secondary Ossification Centers

and Secondary Marrow Cavities


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The Metaphysis

Zone of reserve cartilage = hyaline

cartilage

Zone of proliferation

chondrocytes multiply forming columns offlat lacunae

Zone of hypertrophy = cell enlargement

Zone of calcification

mineralization of matrix

Zone of bone deposition

chondrocytes die and columns fill with

osteoblasts

osteons formed and spongy bone is created

Fetal Skeleton at 12


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Fetal Skeleton at 12

Weeks


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Bone Growth and


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Bone Growth and

Remodeling

Bones increase in length interstitial growth of epiphyseal plate

epiphyseal line is left behind when cartilage gone

Bones increase in width = appositional growth osteoblasts lay down matrix in layers on outer

surface and osteoclasts dissolve bone on innersurface

Bones remodeled throughout life Wolffs law of bone = architecture of bonedetermined by mechanical stresses

action of osteoblasts and osteoclasts

greater density and mass of bone in athletes or

manual worker is an adaptation to stress


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Dwarfism

Achondroplastic long bones stop growing

in childhood normal torso, short limbs

spontaneous mutationduring DNA replication

failure of cartilage growth

Pituitary lack of growth hormone

normal proportions withshort stature

Other Factors


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Other Factors

Affecting Bone Hormones, vitamins and growth factors

Growth rapid at puberty

hormones stimulate osteogenic cells,

chondrocytes and matrix deposition in

growth plate girls grow faster than boys and reach full

height earlier (estrogen stronger effect)

males grow for a longer time and taller

Growth stops (epiphyseal platecloses)

teenage use of anabolic steroids =

premature closure of growth plate and

short adult stature

Fractures and Their


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Fractures and Their

Repair

Stress fracture caused bytrauma

car accident, fall, athletics, etc

Pathological fracture in boneweakened by disease

bone cancer or osteoporosis

Fractures classified bystructural characteristics

break in the skin

multiple pieces

Types of Bone


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Types of Bone

Fractures


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Healing of Fractures 1

Normally 8 - 12 weeks (longer in

elderly)

Stages of healing

fracture hematoma (1) - clot forms, then

osteogenic cells form granulation tissue

soft callus (2)

fibroblasts produce fibers and fibrocartilage

hard callus (3)

osteoblasts produce a bony collar in 6 weeks

remodeling (4) in 3 to 4 months

spongy bone replaced by compact bone


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Healing of Fractures 2


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Documents

Lecture Cartilage and Bone 2009