“Cartilage and Bone

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Cartilage

� Embryo�More prevalent than in

adultadult�Skeleton initially mostly

cartilage�Bone replaces cartilage

in fetal and childhood periods

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BoneNow about bones…like other connective tissue:cells separated by extracellular matrix with collagen but also mineral crystals

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� Remember the three germ tissues1. Ectoderm - epithelial 2. Endoderm - epithelial 2. Endoderm - epithelial 3. Mesoderm is a mesenchyme tissue

� Mesenchyme cells are star shaped and do not attach to one another, therefore migrate freely

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Bones� Functions

� Support� Movement: muscles attach by tendons and use bones

as levers to move body� Protection

� Skull – brain� Skull – brain� Vertebrae – spinal cord� Rib cage – thoracic organs

� Mineral storage� Calcium and phosphorus ( 99% av allt kalcium )� Released as ions into blood as needed

� Blood cell formation and energy storage� Bone marrow: red makes blood, yellow stores fat

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Chemical composition of bones� Cells ( 1 % ), matrix ( nätverk) of collagen

fibers and ground substance (organic: 35%)�Contribute to the flexibility and tensile strength

� Mineral crystals (inorganic: 65%)� Mineral crystals (inorganic: 65%)�Primarily calcium phosphate calciumhydroxid �Lie in and around the collagen fibrils in

extracellular matrix�Contribute to bone hardness

� Small amount of water6PÅL 2011

Classification of bones by shape

� Long bones� Short bones� Flat bones � Irregular � Irregular

bones� Pneumatized

bones� Sesamoid

bones(Short bones include sesmoid bones)

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Benvävnaden har blodkärl, celler (osteocyter, osteoblaster och osteoclaster) och

matrix bestående av organiskt material:kollagen I (armeringsjärn), proteoglykaner och glykoprotein(som man tror bidrar till att matrix kalcifieras).

Oorgansikt material är fr a. calcium och fosfor som tillsammans bildar hydroxyapatit - betong. bildar hydroxyapatit - betong.

Mineraler + kollagena fibrer är det som gör benet hårt.

Gross anatomy of bones

� Compact bone

� Spongy (trabecular) bone

( svampben)

� Blood vessels� Blood vessels

� Medullary cavity

� Membranes� Periosteum� Endosteum

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Periostet: Finns på utsidan av benet.

I periostet finns bindväv och nerver. ( Det gör ont när någon sparkar på benet ).

Periostet innehåller kollagentrådar och fibroblaster samt är täckt av osteprogenitor ”benbildande” celler (ka n omvandlas till osteoblaster).

Sharpe’s trådar förankrar periostet i benet (matrix ).Endost: sitter mellan benet och benmärgen. Består av tunn

bindväv och ett lager osteprogenitor celler.

Funktionen hos periost och endost är fr a att nutri era benvävnaden och tillföra nya osteoblaster för repar ation och tillväxt av ben.

Periosteum� Connective tissue membrane� Covers entire outer surface of bone except at epiphyses� Two sublayers

� 1. Outer fibrous layer of dense irregular connective tissue� 2. Inner (deep) cellular osteogenic layer on the compact bone

containing osteoprogenitor cells (stem cells that give rise to osteoblasts)

� Osteoblasts: bone depositing cells� Osteoblasts: bone depositing cells� Also osteoclasts: bone destroying cells (from the white blood cell line)

� Secured to bone by perforating fibers (Sharpey’s fibers)

Endosteum� Covers the internal bone surfaces� Is also osteogenic

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Structure of a Long Bone

Figure 6.3a-c13PÅL 2011

Flat, Short, Irregular Bones

� Flat Bones� No diaphyses or

epiphyses� Have bone marrow but no

marrow cavity� A sandwich of (spongy) � A sandwich of (spongy)

bone between compact bone

� (Spongy bone)� Composed of bony plates

known as trabeculae

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Spongy (Cancellous) Bone

� NO osteons� Matrix forms open

network of trabeculaetrabeculae

� Trabeculae NOTvascularized

Matrix

byggs upp av osteoblaster som sitter i väggen till märghålan.Där syntetiseras kollagen 1, proteoglykaner och glykoproteiner.

Innan kalcifiering kallas den nybildade benmassan osteoid och ligger i tunt lager framför osteoblasterna.

Ob koncentrerar sedan kalciumsalter vilka läggs på kollagenfibriller.

Ob bygger in sig själva i matrix och omvandlas då till mindre aktiva osteocyter med canaliculi.

(Spongy) Bone

� Trabeculae : interconnecting rods or plates of bone. � Spaces filled with marrow. � Covered with endosteum.� Oriented along stress lines

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Compact Bone

� Composed of osteons (haversarian system) : Basic unit of mature compact bone

�Osteocytes : mature bone cells arranged in �Osteocytes : mature bone cells arranged in concentric lamellae (layers)� Surround a central canal containing blood vessels

(deliver nutrients remove waste)

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Internal structure

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Hur nutrieras benvävnad?

Eftersom metaboliter inte kan diffundera genom den kalcifierade matrixen,

beror utbytet mellan blod och osteocyter på kommunikation genom canaliculi – tunna, cylindriska cytoplasmautskott hos oc som går genom matrix.

Näring tas upp av den första cellen som sänder näringen vidare .

Compact Bone

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Compact bone

� Osteons:� Lamellae:

concentric tubes

� Haversian � Haversian canals

� Osteocytes

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Long bones� Tubular diaphysis or shaft� Epiphyses at the ends: covered with “articular”

(=joint) cartilage� Epiphyseal line in adults

� Kids: epiphyseal growth plate (disc of hyaline cartilage that grows to lengthen the bone)cartilage that grows to lengthen the bone)

� Blood vessels� Nutrient arteries and veins through nutrient� foramen

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Bone Cells

�Osteoblasts�Osteocytes�Osteocytes�Osteoclasts�Stem cells or osteochondral progenitor

cells

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Bone Cells

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Osteoblasten (ob)syntetiserar osteoid (ännu ej kalcifierad benvävnad)och organiskt material i matrix.

Deposition av oorganiskt material beror oxå på ob.Osteoblasten koncentrerar calciumsalter intracellulärt vilket tros påskynda calcifieringsprocessen (calciumsalter på kollagenfibriller).kollagenfibriller).

Ob bygger in sig med benmatrix och omvandlas då till osteocyt (oc) med canaliculi cytoplasmautskott för nutrition).

I benvävnaden finns oc som osteoner (haverska kanalsystem), ringstrukturer av oc runt ett blodkärl.

Bone Cells� Osteoblasts

� Active in bone formation, a process known as ossification or osteogenesis.

� Collagen produced by E.R. and golgi.

� Precursors of hydroxyapetite stored in vesicles,

� Osteocytes� Osteocytes� Essentially osteoblasts that have been

trapped in the matrix� Mature bone cells commonly found in

Iacunae� Carry out the normal metabolic

processes of bone� Found in compact and spongy bone

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Osteoklasten: bryter ned benvävnad. Celler som uppkommer från monocyter från blodet.

Osteoklasten (ok) bryter ned ben genom att bilda en vakuol vid benet.Till vakuolen pumpas H+ in vilket sänker pH-värdet. På så vis bryts hydroxyapatiten ner.

Kollagenas och proteolytiska enzym bryter ned kollagentrådar, proteoglykaner och glykoprotein.

Ok är stora, rörliga, förgrenade och multinukleära (mitos utan cytokines) med många mitokondrier och lysosomer.

Osteoclasts and Stem Cells� Osteoclasts.

� Cells used to breakdown bone (bone resorption) � Ruffled border: where cell membrane borders bone and

resorption is taking place. � H+ ions pumped across membrane, acid forms, breaks down

mineral salts (demineralization)mineral salts (demineralization)� Release enzymes that digest the organic proteins of matrix� Derived from monocytes (which are formed from stem cells in

red bone marrow)� Multinucleated and probably arise from fusion of a number of

cells

� Stem Cells . Mesenchyme (Osteochondral Progenitor Cells ) become chondroblasts or osteoblasts.

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Osteoclast – A Bone-Degrading Cell� A giant cell with many nuclei� Crawls along bone surfaces� Breaks down bone tissue� Breaks down bone tissue

�Secretes concentrated hydrochloric acid

�Lysosomal enzymes are released

Figure 6.13a30PÅL 2011

Bone markings reflect the stresses

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Bone development

� Osteogenesis: “formation of bone” � From osteoblasts� Bone tissue first appears in week 8 (embryo)

� Ossification : “to turn into bone”� Intramembranous ossification ( Direkt benbildning)� forms directly from mesenchyme (not modeled first in � forms directly from mesenchyme (not modeled first in

cartilage)� Most skull bones except a few at base� Clavicles (collar bones)� Sesamoid bones (like the patella)

� Endochondral ossification (Indirekt benbildning)� modeled in hyaline cartilage then replaced by bone

tissue� All the rest of the bones 32PÅL 2011

intramembranös ossifikation: Benet bildas direkt från mesenchymet (vävnad under fosterutvecklingen som ännu inte differentierat) utan broskförlaga.

Startpunkten är primära ossifikationscentra där grupper av celler differentierar till osteoblaster, benmatrix bildas, kalcifikation sker och ob blir osteocyter.Ossifikationscentra växer såsmåningom ihop med Ossifikationscentra växer såsmåningom ihop med andra centra.

-På detta vis bildas platta ben i kroppen dvs frontal-temporal-ossipita benen, mandibeln och maxillen.Även benmanschetten (förtjockning av de långa benen) bildas.

Intramembranous Ossification

� Osteoprogenitor cells aggregate:� differentiate into

osteoblasts (ossification center)(ossification center)

� Osteoblasts secrete organic matrix (what is that?)

� develop projections of trabeculae

Intramembranous Ossification:

� Blood vessels invade area; supply osteoblasts with nutrients

� Trabeculae connect: � trap blood vessels � trap blood vessels

inside bone� Resulting spongy bone is

remodeled into:� osteons of compact

bone� periosteum� or marrow cavities

Endochondral ossification� Modeled in hyaline cartilage, called cartilage

model� Gradually replaced by bone: begins late in second

month of development� Perichondrium is invaded by vessels and

becomes periosteum� Osteoblasts in periosteum lay down collar of bone � Osteoblasts in periosteum lay down collar of bone

around diaphysis� Calcification in center of diaphysis� Primary ossification centers� Secondary ossification in epiphyses� Epiphyseal growth plates close at end of

adolescence� Diaphysis and epiphysis fuse� No more bone lengthening See next slide

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Endochondral ossification

Stages 1-3 during fetal week 9 through 9th

month

Stage 4 is just before birth

Stage 5 is process of long bone growth during childhood & adolescence 37PÅL 2011

Endochondral ossification

� hyaline cartilage is gradually converted to bone� begins in the second month of development

Endochondral ossification

STEP 1�Chondrocytes in the center of hyaline

cartilage:cartilage:� enlarge, lacunae expand� matrix reduced to calcify� nutrients can no longer diffuse through

calcified cartilage.� chondrocytes die, leaving cavities

Endochondral Ossification

STEP 2� Blood vessels grow into

perichondrium

� Cells in the perichondrium � Cells in the perichondrium differentiate into osteoblasts

� osteoblasts begin producing a layer of superficial compact bone around the shaft

� The perichondrium is now renamed the periosteum

Endochondral Ossification

STEP 3� Blood vessels enter the

cartilage�bringing fibroblasts that �bringing fibroblasts that

become osteoblasts�spongy bone develops

at the primary ossification center

Endochondral Ossification

STEP 4� Remodeling creates

a marrow cavity

�osteoclasts erode trabeculae in center of diaphysis, creating marrow cavity

Endochondral Ossification

STEP 5� Capillaries and

osteoblasts enter the epiphyses creating epiphyses creating secondary ossification centers

Endochondral Ossification

STEP 6� Epiphyses fill with spongy

bone:

� remaining cartilage within � remaining cartilage within the joint cavity is articular cartilage (persists throughout life)

� remaining cartilage at the metaphysis is epiphyseal cartilage

endochondral ossifikation:

Broskmodell ersätts av benmodell genom deponering av benmatrix på existerande broskmodell.

Broskmodellen är mjuk vilket underlättar födelse.

Broskskelettet byggs upp av chondrocyter.

Sedan bryter chondroklaster ner chodrocyterna Sedan bryter chondroklaster ner chodrocyterna vilket ger kalcifierat broskmatrix men tomma lakuner (primär fas).Blodkärl bildas i brosket och tar med sig benbildande celler som invaderar brosklakunerna i sekundär fas och blir osteoblaster.

Rörben som femur och humerus bildas på detta sätt.

Epiphyseal growth plates in child, (a), and lines in adult, (b) (see arrows)

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Factors regulating bone growth

� Vitamin D: increases calcium from gut � Parathyroid hormone (PTH): increases

blood calcium (some of this comes out of bone)

� Calcitonin: decreases blood calcium � Calcitonin: decreases blood calcium (opposes PTH)

� Growth hormone & thyroid hormone: modulate bone growth

� Sex hormones: growth spurt at adolescense and closure of epiphyses

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Bone remodeling� Osteoclasts

�Bone resorption

� Osteoblasts�Bone deposition�Bone deposition

� Triggers�Hormonal: parathyroid hormone�Mechanical stress

� Osteocytes are transformed osteoblasts

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Terms (examples)� chondro refers to cartilage

� osteo refers to bone

� blast refers to precursor cell or one that produces somethingproduces something� osteoblast

� cyte refers to cell� osteocyte

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Bone Development

� Osteogenesis and ossification – the process of bone tissue formation, which leads to:�The formation of the bony skeleton in embryos�Bone growth until early adulthood�Bone thickness, remodeling, and repair

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Repair of bone fractures (breaks)

� Simple and compound fractures� Closed and open reduction 51PÅL 2011

The Skeleton Throughout Life� Cartilage grows quickly in youth� Skeleton shows fewer chondrocytes in the

elderly� Bones are a timetable� Bones are a timetable

�Mesoderm – gives rise to embryonic mesenchyme cells

�Mesenchyme – produces membranes and cartilage

�Membranes and cartilage ossify

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The Skeleton Throughout Life� Skeleton grows until the age of 18–21 years� In children and adolescents

�Bone formation exceeds rate of bone reabsorption

In young adults � In young adults �Bone formation and bone reabsorption are in

balance

� In old age reabsorption predominates� Bone mass declines with age

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