CONTENTS  FORMATION OF BONE  CLASSIFICATION OF BONES  STRUCTURE OF BONE  BLOOD SUPPLY  COMPOSITION OF BONE  FRACTURE HEALING  CARTILAGE  TYPES OF CARTILAGE BONE (syn – Os; Osteon)  Osseous tissue, a specialised form of dense connective tissue consisting of bone cells (osteocytes)  Embedded in a matrix of calcified intercelluar substance  Bone matrix contains collagen fibres and the minerals calcium phosphate and calcium carbonate

1. Presenter - Dr. Vinay Jain K

2. CONTENTS
 FORMATION OF BONE
 CLASSIFICATION OF BONES
 STRUCTURE OF BONE
 BLOOD SUPPLY
 COMPOSITION OF BONE
 FRACTURE HEALING
 CARTILAGE
 TYPES OF CARTILAGE

3. BONE (syn – Os; Osteon)
 Osseous tissue, a specialised form of dense connective
tissue consisting of bone cells (osteocytes)
 Embedded in a matrix of calcified intercelluar
substance
 Bone matrix contains collagen fibres and the minerals
calcium phosphate and calcium carbonate

4. FORMATION OF BONE
 The process of bone formation - ossificatiom
 All bone is of mesodermal origin
 Two types of ossification
1. Intramembranous ossification
2. Endochondral ossification

5. INTRAMEMBRANOUS
OSSIFICATION
 Mesenchymal condensation
 Highly vascular
 Laying down of bundles of collagen fibres in the
mesenchymal condensation
 Osteoblast formation – OSTEOID
 Calcium salts deposition – lamellus of bone

6. BONE FORMATION- Intramembranous ossification

7. BONE FORMATION - Intramembranous ossification

8. BONE FORMATION - Intramembranous ossification

9. BONE FORMATION - Intramembranous ossification

10. ENCHONDRAL OSSIFICATION
 Ossifies bones that originate as hyaline cartilge
 Most bones originate as hyaline cartilage
 Growth and ossification of long bones occurs in
6 steps

11. STEP 1
 Chondrocytes in the center
of hyaline cartilage:
– enlarge
– form struts and calcify
– die, leaving cavities in
cartilage

12. STEP 2
 Blood vessels grow around the
edges of the cartilage
• Cells in the perichondrium
change to osteoblasts:
– producing a layer of superficial
bone around the shaft which will
continue to
grow and become compact bone
(appositional growth)

13. STEP 3
 • Blood vessels enter the
cartilage:
– bringing fibroblasts that
become osteoblasts
– spongy bone develops at the
primary ossification center

14. STEP 4
 Remodeling creates a
marrow cavity:
– bone replaces cartilage
at the metaphyses

15. STEP 5
 Capillaries and
osteoblasts
enter the epiphyses:
– creating secondary
ossification centers

16. STEP 6
 Epiphyses fill with
spongy bone:
– cartilage within the
joint cavity is
articulation cartilage
– cartilage at the
metaphysis is epiphyseal
cartilage

17. 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

18. SKELETAL ORGANIZATION
• The actual number of bones in the human skeleton
varies from person to person
• Typically there are about 206 bones
• For convenience the skeleton is divided into the:
• Axial skeleton
• Appendicular skeleton

19. DIVISION OF SKELETON
• Axial Skeleton
• Skull
• Spine
• Rib cage
• Appendicular Skeleton
• Upper limbs
• Lower limbs
• Shoulder girdle
• Pelvic girdle

20. CLASSIFICATION OF BONES BY SHAPE
 Long bones
 Short bones
 Flat bones
 Irregular bones
 Pneumatized
bones
 Sesamoid bones
(Short bones include sesmoid bones)

21. LONG BONES
 Diaphysis – shaft
 Epiphysis – expanded
ends
 Shaft – 3 surfaces, 3
borders, medullary
cavity and a nutrient
foramen directed away
from the growing end
 Ex – humerus, radius,
ulna, femur, etc

22. SHORT BONES
 Are small and thick
 Their shape is usually
cuboid, cuneifrom,
trapezoid or scaphoid
 Ex – carpal and tarsal
bones

23. FLAT BONES
 Are thin with parallel surfaces
• Are found in the skull,
sternum, ribs,and scapula
• Form boundaries of certain body
cavities
• Resembles a sandwich of
spongy bone
• Between 2 layers of compact
bone

24. PNEUMATIC BONES (Gr. – pert. to air)
 Certain irregular bones contain large air spaces lined
by epithelium
 Make the skull light in weight, help in resonance of
voice, and act as air conditioning chambers for
inspired air
 Ex – maxilla, sphenoid, ethmoid, etc

25. SESAMOID BONES
 Resembling a grain of
sesame in size or shape
 Bony nodules found
embedded in the tendons or
joint capsules
 No periosteum and ossify
after birth
 Related to an articular or
nonarticular bony surface
 Ex – patella, pisiform,
fabella, etc
 Functions

26. IRREGULAR BONES
 Have complex shapes
 Examples:
– spinal vertebrae
– pelvic bones

28. DEVELOPEMENTAL CLASSIFICATION
 Membrane (dermal) bones
 Cartilaginous bones
 Membrano-cartilagenous bones

29. Membrane (dermal) bones
 Ossify in membrane (intramembranous of
mesenchymal)
 Derived from mesenchymal condensations
 Ex – bones of the vault of skull and facial bones
 Defect – cleidocranial dysostosis

30. Cartilaginous bones
 Ossify in cartilage (intracartilagenous or
endochondral)
 Derived from preformed cartilaginous models
 Ex – bones of limbs, vertebral column and thoracic
cage
 Defect – common type of dwarfism called
achondroplasia

31. Membrano-cartilaginous bones
 Ossify partly in cartilage and partly in membrane
 Ex – clavicle, mandible, occipital, etc

33. BONE CELLS
 ELEMENTS COMPRISING BONE TISSUE
1. It consists of bone cells or osteocytes – separated by
intercellular substance
2. Osteoblasts – bone producing cells
3. Osteoclasts – bone removing cells
4. Osteoproginator cells – from which osteoblasts and
osteoclasts derived

34. CELLS OF BONE TISSUE

35. OSTEOPROGENITOR CELLS
 Mesenchymal stem cells
that divide to produce
osteoblasts
• Are located in inner,
cellular layer of
periosteum
(endosteum)
• Assist in fracture repair

36. OSTEOBLASTS (Gr.- osteon-bone, blastos – germ)
 Immature bone cells that
secrete matrix compounds
(osteogenesis)
 Osteoid
• Matrix produced by
osteoblasts, but not yet
calcified to form bone
• Osteoblasts surrounded
by bone become
osteocytes

37. OSTEOCYTE
 Mature bone cells that
maintain the bone matrix
• Live in lacunae
• Are between layers
(lamellae) of matrix
• Connect by cytoplasmic
extensions through canaliculi
in lamellae
• Do not divide

38. OSTEOCLAST(Gr.- osteon–bone, +klan-to break)
• Secrete acids and protein
digesting enzymes
• Giant, mutlinucleate cells
• Dissolve bone matrix and
release stored minerals
(osteolysis)
• Are derived from stem cells
that produce macrophages

39. STRUCTURAL CLASSIFICATION
 Macroscopically
1. Compact bone
2. Cancellous bone

40. COMPACT BONE
 Strong dense – 80% of the
skeleton
 Consists of multiple osteons
(haversian systems) with
intervening interstitial lamellae
 Best developed in the cortex of
long bones
 Osteons are made up of
concentric bone lamellae with a
central canal (haversian canal)
containing osteoblasts and an
arteriole supplying the osteon

42. Contd.
 Lamellae are connected by
canaliculi
 Cement lines mark outer
limit of osteon (bone
resorption ended)
 Volkmann’s canals: radially
oriented, have arteriole, and
connect adjacent osteons
 This is an adaptation to
bending and twisting forces
(compression, tension and
shear)

43. OSTEON
 The basic unit of
mature compact
bone
• Osteocytes are
arranged in
concentric
lamellae
• Around a central
canal containing
blood vessels

47. CANCELLOUS BONE
(SPONGY OR TRABECULAR)
 Open in texture – meshwork of trabeculae (rods and plates)
 Crossed lattice structure, makes up 20% of the skeleton
 High bone turnover rate
 Bone is resorbed by osteoclasts in Howship’s lacunae and
formed on the opposite side of the trabeculae by osteoblasts
 Osteoporosis is common in cancellous bone, making it
susceptible to fractures
 Commonly found in the metaphysis and epiphysis of long
bones
 Adaptation to compressive forces

48. Contd.
 Does not have osteons
• The matrix forms an
open network of
trabeculae
• Trabeculae have no
blood vessels

50. Cancellous Bone

51.  Microscopically
1. Lamellar bone
2. Woven bone

52. LAMELLAR BONE
 Bone is made up of layers or lamellae
 Lamellae – is a thin plate of bone consisting of
collagen fibres and mineral salts, deposited in
gelatinous ground substance
 Between adjoining lamellae we see small flattened
spaces – lacunae

53. LAMELLAR
BONE

54. Contd.
 Lacunae
1. Contains one osteocyte
2. Have fine canals or canaliculi that communicate with
those from other lacunae
 Fibers of one lamellus run parallel to each other, but
those of adjoining lamellae run at varying angles to
each other.

55. WOVEN BONE
 Found in all newly formed bone – later replaced by
lamellar bone
 Collagen fibres are present in bundles - run randomly
– interlacing with each other
 Abnormal persistence – paget’s disease

56. Primary
Immature
Woven
Secondary
Mature
Lamellar
MICROSCOPIC
MACROSCOPIC

58. GROSS STRUCTURE OF AN ADULT
LONG BONE
 Shaft
 Two ends

59. SHAFT
 Composed of
1. periosteum,
2. cortex and
3. medullary cavity

60. PERIOSTEUM
 External surface of any bone covered by a membrane –
periosteum
 Two layer
 Outer – fibrous membrane, inner – cellular
 In young bones – inner layer – numerous osteoblasts –
osteogenitic layer
 In adults – osteoblasts are not conspicuous, but
osteoprogeniter cells present here can form osteoblasts
when need arises

61. PERIOSTEUM

62. PERIOSTEUM

63. FUNCTIONS
 Medium through which mucles, tendons and
ligaments are attached
 Forms a nutritive function
 Can form bone when required
 Forms a limiting membrane that prevents bone tissue
from ‘spilling out’ into neighbouring tissues

64. CORTEX
 Is made up of a compact bone which gives the
desired strength
 Can withstand all possible mechanical strains

65. ENDOSTEUM
 • An incomplete cellular layer:
– lines the marrow cavity
– covers trabeculae of spongy
bone
– lines central canals
• Contains osteoblasts,
osteoprogenitor cells, and
osteoclasts
• Is active in bone growth and
repair

66. MEDULLARY CAVITY
Filled with red or yellow bone marrow
1. Red – at birth – haemopoiesis
2. Yellow – as age advance – atrophies – fatty
3. Red marrow persists in the cancellous ends of long
bones

68. PARTS OF YOUNG BONE
 It ossifies in 3 parts
 The two ends from the secondary centers
 Intervening shaft from a primary center

69. EPIPHYSIS
(Gr., a growing upon)
 The ends of a bone which ossify from secondary
centers
 Types
1. Pressure epiphysis – transmission of the weight . Ex-
head of femur, etc
2. Traction epiphysis – provides attachment to one or
more tendons which exerts a traction on the
epiphysis. Ex- trochanters of femur,et

70. 3. Atavistic epiphysis – phylogenitically an
independent bone , which fuses to another bone. Ex-
coracoid process of scapula,etc
4. Aberrant epiphysis – not always present. Ex- head
of the 1st metacarpal and base of other metcarpal

71. DIAPHYSIS
(Gr., a growing through)
 It is the elongated shaft of a long bone which ossifies
from a primary center
 Made of thick cortical bone
 Filled with bone marrow

72. METAPHYSIS
(Gr. meta, after, beyond, + phyein, to grow)
 Epiphysial ends of a diaphysis
 Zone of active growth
 Typically made of cancellous bone
 Hair pin bends of end arteries

73. EPIPHYSIAL PLATE OF CARTILAGE
 It separates epiphysis from the metaphysis.
 Proliferation – responsible for lengthwise growth of
the long bone
 Epiphysial fusion – can no longer grow
 Nourished by both epiphysial and metaphysial arteries

77. BLOOD SUPPLY OF BONES
 LONG BONES – derived from
1. Nutrient artery
2. Periosteal artery
3. Epiphysial artery
4. Metaphysial artery

78. Nutrient artery
1. Enters through the nutrient foramen
2. Divides into ascending and descending branches
in the medullary cavity
3. Branch divides – small parallel channels –
terminate in adult metaphysis
4. Anastomosing with the epiphysial, metaphysial
and periosteal arteries
5. Supplies the medullary cavity , inner 2/3 of the
cortex and metaphysis
6. Nutrient foramen is directed away from the
growing end of the bone

80.  Periosteal arteries
1. Numerous beneath the
muscular and
ligamentous
attachments
2. Ramify beneath the
periosteum and enter
the volkmann’s canals
to supply the outer 1/3
of the cortex

82.  Epiphysial arteries
1. Derieved from periarticular vascular arcades
(circulus vasculosus)
2. Out of the numerus vascular foramina in this region
– few admit arteries and rest venous exits
3. Number size – idea of the relative vascularity of the
two ends of long bone

83.  Metaphysial arteries
1. Derived from the neighbouring systemic vessels
2. Pass directly into the metphysis and reinforce the
metaphysial branches from the primary nutrient
artery

85. HOMEOSTASIS OF BONE TISSUE
• Bone Resorption – action of
osteoclasts and parathyroid
hormone aka parathormone
aka PTH
• Bone Deposition – action of
osteoblasts and calcitonin
• Occurs by direction of the
thyroid and parathyroid
glands
MC
OC

86. FACTORS AFFECTING BONE TISSUE
• Deficiency of Vitamin A – retards bone development
• Deficiency of Vitamin C – results in fragile bones
• Deficiency of Vitamin D – rickets, osteomalacia
• Insufficient Growth Hormone – dwarfism
• Excessive Growth Hormone – gigantism, acromegaly
• Insufficient Thyroid Hormone – delays bone growth
• Sex Hormones – promote bone formation; stimulate
ossification of epiphyseal plates
• Physical Stress – stimulates bone growth

88. CHEMICAL ANALYSIS OF BONE

89. APPLIED ANATOMY
 Periosteum is particularly sensitive to tearing or
tension –
1. Drilling into the compact bone without anaesthesia
causes only dull pain
2. Drilling into spongy bone is much more painful
3. Fractures, tumours and infections of the bone are
very painful
 Blood supply of bone is so rich that it is very difficult
to sufficiently to kill the bone

90. Contd.
 In rickets – calcification of cartilage fails and
ossification of the growth zone is disturbed
1. Osteoid tissue is formed normally and the cartilage
cells proliferate freely ,
2. Mineralization does not takes place
 Scurvy – formation of collagenous fibres and matrix
is impaired
 Osteoporosis - Bone resorption proceeds faster than
deposition

91. FRACTURE HEALING
 STAGES OF FRACTURE HEALING
1. Stage of inflammation
2. Stage of soft callous formation
3. Stage of hard callous formation
4. Stage of remodelling

92. STAGE OF INFLAMMATION

93. STAGE OF SOFT CALLUS
FORMATION

94. STAGE OF HARD CALLUS
FORMATION

95. STAGE OF REMODELLING

96. MECHANISM OF BONE HEALING
 Direct (primary) bone healing
 Indirect (secondary) bone healing

97. DIRECT BONE HEALING
 Mechanism of bone healing seen when there is no motion at the
fracture site (i.e. absolute stability)
 Does not involve formation of fracture callus
 Osteoblasts originate from endothelial and perivascular cells
 A cutting cone is formed that crosses the fracture site
 Osteoblasts lay down lamellar bone behind the osteoclasts
forming a secondary osteon
 Gradually the fracture is healed by the formation of numerous
secondary osteons
 A slow process – months to years

99. INDIRECT BONE HEALING
 Mechanism for healing in
fractures that have some
motion, but not enough to
disrupt the healing process
 Bridging periosteal (soft) callus
and medullary (hard) callus
re-establish structural
continuity
 Callus subsequently undergoes
endochondral ossification
 Process fairly rapid - weeks

100. BONE REMODELLING
 WOLFF’s LAW – remodeling occurs in response to
mechanical stress
1. Increasing mechanical stress increases bone gain
2. Removing external mechanical stress increases bone
loss which is reversible on (to varying degrees) on
remobilzation

101. Contd.
 PIEZOELECTERIC REMODELING – occurs in
response to electric charge
1. The compression side of bone is electronegative
stimulating osteoblasts
2. Tension side of the bone is electropositive,
stimulating osteoclasts

103. CARTILAGE (L.-cartilago – gristle)
 It is a connective tissue composed of cells
(chondrocytes) and fibres (collagen) in matrix, rich in
mucopolysaccarides
 Groung substance – chemically GAG
 Core protein – aggrecan
 Collagen – type 2
 Fibrocartilage and perichondrium – type 1

104. General features
 Has no blood vessels or lymphatics
 Nutrition is by diffusion through matrix
 No nerves – insensitive
 Surrounded by a fibrous membrane – perichondrium
 Articular cartilage has no perichondrium –
regeneration after injury inadequate
 When calcifies – chondrocytes die – replaced by bone

105. TYPES
 HYALINE CARTILAGE
 FIBROCARTILAGE
 ELASTIC CARTILAGE

107. HYALINE CARTILAGE
(G. hyalos - transparent stone)
 Bluish white and transparent due to very fine collagen
fibres
 Abundantly distributed – tendency to calcify after
40yrs of age
 All cartilage bones are preformed in hyaline cartilage
 Ex – articular cartilage, costal cartilage

110. FIBROCARTILAGE
 White and opaque due to abundance of dense collagen
fibres
 Whenever fibres tissue is subjected to great pressure –
replaced by fibrocartilage
 Tough, strong and resilient
 Ex – intervertebral disc, intraarticular disc

111. Fibrocartilage

112. ELASTIC CARTILAGE
 Made of numerous cells and
 Rich network of yellow elastic fibres pervading the
matrix – so that it is more pliable
 Cartilage in the external ear, auditory tube

113. Elastic cartilage

114. THANK YOU