Cartilage and Bone 1 PÅL 2011

Transkript

1 Cartilage and Bone 1

2 Cartilage Embryo More prevalent than in adult Skeleton initially mostly cartilage Bone replaces cartilage in fetal and childhood periods 2

3 Now about bones like other connective tissue:cells separated by extracellular matrix with collagen but also mineral crystals Bone 3

4 Remember the three germ tissues 1. Ectoderm - 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 4

5 Bones Functions Support Movement: muscles attach by tendons and use bones as levers to move body Protection 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 5

6 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%) Primarily calcium phosphate calciumhydroxid Lie in and around the collagen fibrils in extracellular matrix Contribute to bone hardness Small amount of water 6

7 Classification of bones by shape Long bones Short bones Flat bones Irregular bones Pneumatized bones Sesamoid bones (Short bones include sesmoid bones) 7

8 8

9 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. Mineraler + kollagena fibrer är det som gör benet hårt.

10 Gross anatomy of bones Compact bone Spongy (trabecular) bone ( svampben) Blood vessels Medullary cavity Membranes Periosteum Endosteum 10

11 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 (kan 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 nutriera benvävnaden och tillföra nya osteoblaster för reparation och tillväxt av ben.

12 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 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 12

13 Structure of a Long Bone Figure 6.3a-c 13

14 Flat, Short, Irregular Bones Flat Bones No diaphyses or epiphyses Have bone marrow but no marrow cavity A sandwich of (spongy) bone between compact bone (Spongy bone) Composed of bony plates known as trabeculae 14

15 Spongy (Cancellous) Bone NO osteons Matrix forms open network of trabeculae Trabeculae NOT vascularized

16 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.

17 (Spongy) Bone Trabeculae: interconnecting rods or plates of bone. Spaces filled with marrow. Covered with endosteum. Oriented along stress lines 17

18 Compact Bone Composed of osteons (haversarian system): Basic unit of mature compact bone Osteocytes: mature bone cells arranged in concentric lamellae (layers) Surround a central canal containing blood vessels (deliver nutrients remove waste) 18

19 Internal structure 19

20 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.

21 Compact Bone 21

22 Compact bone Osteons: Lamellae: concentric tubes Haversian canals Osteocytes 22

23 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) Blood vessels Nutrient arteries and veins through nutrient foramen 23

24 Bone Cells Osteoblasts Osteocytes Osteoclasts Stem cells or osteochondral progenitor cells 24

25 Bone Cells 25

26 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). 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.

27 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 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 27

28 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 phvärdet. 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.

29 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) 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. 29

30 Osteoclast A Bone-Degrading Cell A giant cell with many nuclei Crawls along bone surfaces Breaks down bone tissue Secretes concentrated hydrochloric acid Lysosomal enzymes are released Figure 6.13a 30

31 Bone markings reflect the stresses 31

32 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 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 32

33 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 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.

34 Intramembranous Ossification Osteoprogenitor cells aggregate: differentiate into osteoblasts (ossification center) Osteoblasts secrete organic matrix (what is that?) develop projections of trabeculae

35 Intramembranous Ossification: Blood vessels invade area; supply osteoblasts with nutrients Trabeculae connect: trap blood vessels inside bone Resulting spongy bone is remodeled into: osteons of compact bone periosteum or marrow cavities

36 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 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 36

37 Endochondral ossification Stages 1-3 during fetal week 9 through 9 th month Stage 4 is just before birth Stage 5 is process of long bone growth during childhood & adolescence 37

38 Endochondral ossification hyaline cartilage is gradually converted to bone begins in the second month of development

39 Endochondral ossification STEP 1 Chondrocytes in the center of hyaline cartilage: enlarge, lacunae expand matrix reduced to calcify nutrients can no longer diffuse through calcified cartilage. chondrocytes die, leaving cavities

40 Endochondral Ossification STEP 2 Blood vessels grow into 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

41 Endochondral Ossification STEP 3 Blood vessels enter the cartilage bringing fibroblasts that become osteoblasts spongy bone develops at the primary ossification center

42 Endochondral Ossification STEP 4 Remodeling creates a marrow cavity osteoclasts erode trabeculae in center of diaphysis, creating marrow cavity

43 Endochondral Ossification STEP 5 Capillaries and osteoblasts enter the epiphyses creating secondary ossification centers

44 Endochondral Ossification STEP 6 Epiphyses fill with spongy bone: remaining cartilage within the joint cavity is articular cartilage (persists throughout life) remaining cartilage at the metaphysis is epiphyseal cartilage

45 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 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.

46 Epiphyseal growth plates in child, (a), and lines in adult, (b) (see arrows) 46

47 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 (opposes PTH) Growth hormone & thyroid hormone: modulate bone growth Sex hormones: growth spurt at adolescense and closure of epiphyses 47

48 Bone remodeling Osteoclasts Bone resorption Osteoblasts Bone deposition Triggers Hormonal: parathyroid hormone Mechanical stress Osteocytes are transformed osteoblasts 48

49 Terms (examples) chondro refers to cartilage osteo refers to bone blast refers to precursor cell or one that produces something osteoblast cyte refers to cell osteocyte 49

50 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 50

51 Repair of bone fractures (breaks) Simple and compound fractures Closed and open reduction 51

52 The Skeleton Throughout Life Cartilage grows quickly in youth Skeleton shows fewer chondrocytes in the elderly Bones are a timetable Mesoderm gives rise to embryonic mesenchyme cells Mesenchyme produces membranes and cartilage Membranes and cartilage ossify 52

53 The Skeleton Throughout Life Skeleton grows until the age of years In children and adolescents Bone formation exceeds rate of bone reabsorption In young adults Bone formation and bone reabsorption are in balance In old age reabsorption predominates Bone mass declines with age 53