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
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
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
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
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
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
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
41.
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
44.
45.
46.
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
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
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
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
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
67.
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
74.
75.
76.
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
79.
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
81.
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
84.
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
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
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
98.
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
102.
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
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
108.
109.
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
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