1  

The  Skeletal  System:  Bone  Tissue  

BIOL  121:  A&P  I  Chapter  6

Rob  Swatski  Associate  Professor  of  Biology  

HACC  –  York  Campus  Textbook images - Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

2  

3  

Skeletal  System  Tissues  

Bone   Car)lage   Dense  CT   Epithelium   Adipose   Nervous  

4  

5  

FuncLons  of  Bone  

Supports  body  

Protects  so?  )ssues  

Muscle  aAachment  

site  

6  

FuncLons  of  Bone,  cont.  

Mineral  storage  &  

homeostasis  

Produces  blood  cells  in  red  bone  marrow  

(hemopoiesis)  

Energy  storage  in  yellow  bone  marrow  

7  

8  

Bone  Marrow  

9  

10  

Anatomy  of  a  Long  Bone  

11  

Anatomy  of  a  Long  Bone  

Diaphysis  

Epiphysis  

Metaphysis  

Epiphyseal  plate  

ArLcular  carLlage  

(b) Partially sectioned humerus

Medullary cavity in diaphysis

Compact bone

Spongy bone Epiphyseal line

Proximal epiphysis

Metaphysis

13  

Anatomy  of  a  Long  Bone,  cont.  

Medullary  (Marrow)  cavity  

Endosteum  

Periosteum  

Fibrous  layer  

Osteogenic  layer  

14  

15  

16  

Histology  of  Bone  Tissue  

Compact  bone  

Spongy  bone  

Specialized  bone  cells  

Extracellular  matrix  

17  

18  

Matrix  

15%  water,  30%  collagen,  55%  mineral  salts  

Calcium  phosphate  (hydroxyapa)te),  calcium  carbonate,  

K,  Mg      

Collagen  fiber  skeleton    

=  tensile  strength  

CalcificaLon  (MineralizaLon)    

=  hardness  

19  

20  

4  Types  of  Bone  Cells  

Osteogenic  cells  

Osteoblasts  

Osteocytes  

Osteoclasts  

21  

Osteogenic  Cells  

=  Osteoprogenitor  cells  

Undifferen)ated  

Periosteum  &  endosteum  

Develop  into  osteoblasts  

22  

Osteoblasts  

Bone-­‐building  cells  

Do  not  divide  

Form  bone  matrix  &  secrete  collagen  fibers  

Develop  into  osteocytes  

23  

Osteocytes  

Mature  bone  cells  

Maintain  bone  )ssue  

No  longer  secrete  matrix  

24  

25  

Osteoclasts  

Largest  of  the  bone  cells  

Originate  from  fused  monocytes  

(wbc’s)  

Bone  resorpLon  

26  

27  

Compact  (Dense)  Bone  

Solid,  hard,  external  layer  

of  bone  

Forms  diaphysis  of  long  bones  

Resists  stresses  of  weight  &  movement  

Arranged  in  units  called  osteons  

28  

Osteons  

=  Haversian  systems  

Osteocytes  

Abundant  vascular  )ssue:  blood  vessels  &  lympha)cs  

Nervous  )ssue  

(a)  Osteons  (haversian  systems)  in  compact  bone  and  trabeculae  in  spongy  bone  

Compact bone Spongy bone Periosteum

Medullary cavity

Outer circumferential lamellae

Interstitial lamellae Concentric

lamellae

Blood vessels

Canaliculi

Osteocyte

Lacuna

Periosteal vein Periosteal artery

Periosteum: Outer fibrous layer Inner osteogenic layer

Central canal

Compact bone

Spongy bone

Inner circumferential lamellae

Trabeculae

Medullary cavity

See Figure 6.3b for details

Perforating canal Perforating (Sharpey’s) fibers

Osteon

30  

Osteon  Histology  

Concentric  lamellae  of  matrix  around  central  canal  

Osteocytes  inside  lacunae  

Canaliculi  

IntersLLal  lamellae  

31  

32  

33  

Spongy  Bone  No  osteons  

Consists  of  trabeculae  

Supports  red  bone  marrow  

Reduces  weight  

Short,  flat,  irregular  bones  

Epiphyses  of  long  bones  

34  

35  

36  

Blood  Supply  of  Bone    Periosteal  arteries  

Nutrient  arteries  

Epiphyseal  arteries  

Metaphyseal  arteries  

37  

Bone  FormaLon  (OssificaLon)  

Embryonic  CT  begins  as  mesenchyme  

Template  for  ossifica)on  

Intramembranous  ossificaLon  

Endochondral  ossificaLon  

38  

39  

Intramembranous  OssificaLon  

Forms  flat  bones  of  skull  &  mandible  

“Jelly  sandwich”  

Mesenchyme  à  Osteogenic  cells  

Ossifica)on  center  

Osteoblasts  à  Matrix  (Calcifica)on)  

Osteoblasts  à  Osteocytes  

Osteogenic  cells  

40  

41  Osteoblasts  

42  

Intramembranous  OssificaLon,  cont.  

Calcifying  matrix  joins  to  form  trabeculae  

Spongy  bone  forms  around  red  bone  marrow  

Surface  mesenchyme  à  Periosteum  

Superficial  spongy  bone  à  Compact  bone  

43  

Flat bone of skull

Mandible

Blood capillary

Ossification center

Mesenchyme

Osteoblast

Collagen fiber Development of ossification center: osteoblasts secrete organic extracellular matrix

1

Osteocyte in lacuna

Calcification: calcium and other mineral salts are deposited and extracellular matrix calcifies (hardens)

2

Canaliculus

Osteoblast

Newly calcified bone extracellular matrix

Mesenchyme condenses

Formation of trabeculae: extracellular matrix develops into trabeculae that fuse to form spongy bone

3

Blood vessel Spongy bone trabeculae

Osteoblast

Periosteum

Compact bone tissue

Spongy bone tissue

Compact bone tissue

Development of the periosteum: mesenchyme at the periphery of the bone develops into the periosteum

4

45  

Endochondral  OssificaLon  

Forms  longs  bones  

Replaces  car)lage  with  bone  

Six  step  process  

Begins  with  forma)on  of  carLlage  model  

46  

1.  Development  of  CarLlage  

Model  

Originates  from  mesenchyme  

Basic  shape  and  length  of  bone  

Hyaline  car)lage  &  chondroblasts  

Perichondrium  

47  

2.  Growth  of  CarLlage  Model  

Chondrocytes  divide  &  matrix  forms  

IntersLLal  growth  

ApposiLonal  growth  

Mid-­‐region  cells  burst  &  lower  pH  

Destroys  chondrocytes  &  triggers  calcifica)on  

48  

3.  Development  of  Primary  OssificaLon  

Center  

Perichondrium  à  Periosteum  

Forms  periosteal  bone  collar  

Nutrient  artery  penetrates  center  of  bone  model  

Periosteal  bud  brings  osteoblasts  &  osteoclasts  to  

center  

49  

50  

4.  Development  of  Medullary  

Cavity  

Osteoblasts  deposit  matrix  over  calcified  car)lage  

Form  trabeculae  of  spongy  bone  

Osteoclasts  form  medullary  cavity  

51  

5.  Development  of  Secondary  OssificaLon  

Center  Blood  vessels  enter  uncalcified  epiphyses  

Spongy  bone  develops  

52  

6.  FormaLon  of  ArLcular  CarLlage  

&  Epiphyseal  Plate  

Epiphyseal  car)lage  does  not  ossify  

Remains  as  arLcular  carLlage  

Epiphyseal  (Growth)  plate  also  remains  as  car)lage  

Source  of  inters))al  growth  

Development of cartilage model: mesenchymal cells develop into chondroblasts, which form the cartilage model.

1

Proximal epiphysis

Diaphysis

Distal epiphysis

Hyaline cartilage

Perichondrium

Endochondral Ossification - Overview

Growth of cartilage model: growth occurs by cell division of chondrocytes.

2

Uncalcified extracellular matrix

Calcified extracellular matrix

Nutrient artery

Periosteum

Primary ossification center

Spongy bone

Development of primary ossification center: in this region of the diaphysis, bone tissue replaces most of the cartilage.

3

Uncalcified extracellular matrix

Development of the medullary (marrow) cavity: bone breakdown by osteoclasts forms the medullary cavity.

4

Calcified extracellular matrix

Periosteum

Medullary cavity

Nutrient artery and vein

Development of secondary ossification centers: these occur in the epiphyses of the bone.

5

Secondary ossification center

Uncalcified extracellular matrix

Epiphyseal artery and vein

Articular cartilage

Spongy bone

Epiphyseal plate

Formation of articular cartilage and epiphyseal plate: both structures consist of hyaline cartilage.

6

Endochondral Ossification – Overview, cont.

(b) Twelve-week fetus. The red areas represent bones that are forming (calcified). Clear areas represent cartilage (uncalcified).

56  

Epiphyseal  (Growth)  Plate  

Chondrocytes  produce  carLlage  on  epiphyseal  side  

Car)lage  replaced  by  bone  on  diaphyseal  side  

Plate  closes  at  age  18-­‐25  

Chondrocytes  stop  dividing  

Bone  replaces  car)lage  (epiphyseal  line)  

57  

4  Zones  of  Epiphyseal  Plate  

Zone  of  ResLng  CarLlage  

Zone  of  ProliferaLng  CarLlage  

Zone  of  Hypertrophic  CarLlage  

Zone  of  Calcified  CarLlage  

Epiphysis

(c) Lengthwise growth of bone at epiphyseal plate

EPIPHYSEAL (GROWTH) PLATE:

Zone of resting cartilage Zone of proliferating cartilage Zone of hypertrophic cartilage

Zone of calcified cartilage

Diaphysis

Articular cartilage

New chondrocytes are formed

Old chondrocytes are replaced by bone

New diaphysis

59  

Zone  of  ResLng  CarLlage  Anchors  growth  plate  

to  bone  

60  

Zone  of  ProliferaLng  CarLlage  

Rapid  cell  division  (stacks  of  coins)  

61  

Zone  of  Hypertrophic  CarLlage  Cells  enlarge  &  

remain  in  columns  

62  

Zone  of  Calcified  CarLlage  Thin  zone  –  mostly  

dead  cells  

Osteoblasts  &  osteoclasts  ac)ve  

63  

Calcified  CarLlage  

Ridges in periosteum create groove for periosteal blood vessel.

1

Periosteal ridges

Periosteum

Periosteal blood vessel

Perforating canal

Groove

Periosteal ridges fuse, forming an endosteum-lined tunnel.

2

Endosteum

Tunnel

Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon.

3

Endosteum

Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.

4

Circumferential lamellae Periosteum

New osteon

Central (haversian) canal

Ridges in periosteum create groove for periosteal blood vessel.

1

Periosteal ridges

Periosteum

Periosteal blood vessel

Perforating canal

Groove

Periosteal ridges fuse, forming an endosteum-lined tunnel.

2

Endosteum

Tunnel

Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon.

3

Endosteum

Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.

4

Circumferential lamellae

Periosteum

New osteon

Central (haversian) canal

Medullary cavity

Bone formed by osteoblasts

Bone destroyed by osteoclasts

Infant Child Young adult

Adult

(b) Macroscopic changes

70  

Factors  AffecLng  Bone  

Growth:  Nutri&on  

Calcium  &  Phosphorus  

Vitamin  C  à  collagen  

Vitamins  K  &  B12  à  protein  synthesis  

71  

Factors  AffecLng  Bone  

Growth:  Hormones  

Insulinlike  Growth  Factors  (IGFs)  

Thyroid  hormone,  hGH,  insulin  

Estrogen  &  testosterone  

72  

Bone  Homeostasis  

Remodeling  

Osteoclasts  

Osteoblasts  

73  

OrthodonLcs  

74  

The  Effects  of  Corsetry  

75  

Bone  Fractures  

Greens)ck  

Impacted  

Open  

Comminuted  

PoA  

Colles’  

Stress  

Ulna

Greenstick

Radius

Wrist bones

Humerus

Impacted

Humerus

Open (Compound)

Radius

Ulna

Humerus

Comminuted

Tibia

Pott

Fibula

Ankle bones

Ulna

Colles’

Radius

Wrist bones

82  

Fracture  Repair  

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Periosteum

Fracture hematoma

Fibrocartilaginous callus (soft)

Reactive phase: formation of fracture hematoma

1 Reparative phase: fibrocartilaginous callus formation

2a Reparative phase: bony callus formation

2b Bone remodeling phase

3

New blood vessel

Spongy bone trabeculae

Bony (hard) callus

Healed fracture

84  

1.  Reac&ve  Phase:  FormaLon  of  fracture  hematoma  (clot)  

85  

2.  Repara&ve  Phase:  FibrocarLlaginous    callus  formaLon  

86  

3.  Repara&ve  Phase:  Bony  callus  formaLon  

87  

4.  Bone  Remodeling  Phase  

88  

Calcium  Homeostasis  &  Bone  Tissue  

Skeleton  =  Calcium  reservoir  

Nerve  &  muscle  fiber  func)on  

Blood  clohng  cascade  

Enzyme  func)on  

9-­‐11  mg  Ca+2/100  ml  plasma  

89  

Hormonal  RegulaLon  of  

Ca+2  Parathyroid  Hormone  

(PTH)  

Calcitriol  

Calcitonin  

STIMULUS

CONTROLLED CONDITION Blood calcium (Ca2+) level

RECEPTORS

CONTROL CENTER Parathyroid hormone gene

EFFECTORS

RESPONSE Increase in blood Ca2+ level

Osteoclasts increase

bone resorption

Kidneys retain Ca2+ in blood, excrete phosphate in urine, and produce calcitriol

Parathyroid gland cells

Return to homeostasis when response brings blood Ca2+ level back to normal

Disrupts homeostasis by decreasing

Detect lowered Ca2+ concentration which increases production of cyclic AMP

Input

Output Gene “turned on” which increases release of PTH

Osteoclasts Kidneys

91  

How  do  they  do  this?  

92  

Aging  &  Bone  Tissue  

Demineraliza)on  

Osteoporosis  

Reduced  protein  synthesis  

Less  collagen  

Less  growth  hormones  

93  

94  

Disorders  of  Bone  

OssificaLon  

RickeAs  

Osteomalacia  

95  The  End