BONES AND BONE TISSUES
CHAPTER 6
9/16/07
Introduction
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One of the most remarkable tissues of the
human body
Far from inert and lifeless, bones are
living, dynamic structures
Bones serve a wide variety of very diverse
functions within us
Noted for their strength and resiliency
during life, bones will remain long after
we are gone
Chapter Outline
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Skeletal cartilages
Bones
Disorders of bones
The skeleton throughout life
Location and Basic Structure
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Cartilages are
found throughout
the adult human
body
Location and Basic Structure
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Initially our skeleton is made up of fast
growing cartilages and fibrous
membranes
Gradually our skeletal cartilages are
replaced by bone
Upon reaching adulthood the skeleton
becomes almost fully ossified
Only a few cartilages remain in the adult
skeleton
Location and Basic Structure
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A typical cartilage is composed of
connective tissue cartilage
It contains no nerves or blood vessels
It is surrounded by a layer of dense
irregular connective tissue called the
perichondrium which resists outward
expansion of the tissue when subjected to
pressure
Location and Basic Structure
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Each type of cartilage contains a high
proportion of water which makes them
resilient after compression
Cartilage is 60-80% water
The water allows nutrients to diffuse
rapidly through a loose matrix
Basic structure, type & location
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There are three types of cartilage tissue:
hyaline, elastic, and fibrocartilage
Each type consists of chondrocytes living
in an extracellular matrix
Each contains a matrix of jellylike
ground substance of complex sugar
molecules that attract and hold water
that is laced with connective tissue fibers
Hyaline cartilages
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The most prevalent type of cartilage
Its high proportion of collagen fibers give
it flexibility and resilience while
providing support
Upon examination the tissue appears
white, frosted, and smooth
Hyaline cartilages
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The chondrocytes appear spherical
Each chondrocyte occupies a cavity in the
matrix called a lacuna
The only type of fiber in the matrix is a
collagen unit fibril
Hyaline cartilage locations
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Articular - covers the end of bones
Costal - connect ribs to breastbone
Laryngeal - skeleton of larynx
Tracheal & bronchial - reinforce the
respiratory passages
Fetal - forms the embryonic skeleton
Elastic cartilage
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Elastic cartilage is similar to hyaline
cartilage but its matrix contains many
more elastic fibers in addition to collagen
fibers
Its elastic fibers enable it to withstand
repeated bending
Found only in the external ear and the
epiglottis
Fibrocartilage
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The tissue consists of parallel rows of
thick collagen fibers alternating with
rows of chondrocytes
Tissue is highly compressible and has
great tensile strength
Found in thick pad-like structures like
the menisci of the knee or the discs of the
vertebral column
Growth of Cartilage
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A cartilage grows in two ways
Appositional growth occurs when cells in
the surrounding perichondrium secrete
new matrix next to existing cartilage
tissue (growth from the outside)
Interstitial growth occurs when the
chondrocytes within the cartilage divide
and secrete new matrix, expanding the
cartilage (growth from within)
Growth of Cartilage
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Cartilage stops growing in the late teens
when the skeleton itself stops growing
Chondrocytes stop dividing and growth
stops
Cartilage regenerates poorly in adults
with most of the “healing” reflecting the
ability of the remaining chondrocytes to
secrete additional extracellular matrix
BONES
SECTION II
Bones
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Bones of the skeleton are organs that
contain several different tissues
Bones are dominated by bone tissue but
also contain
–
–
–
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Nervous tissue and nerves
Blood tissue and vessels
Cartilage in articular cartilages
Epithelial tissue lining the blood vessels
Function of Bones:
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Bones perform several important
functions:
–
–
–
–
–
Support
Movement
Protection
Mineral storage
Blood cell formation and energy storage
Function of Bones
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Support
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Bones provide a hard
framework that
supports the body
Bones provide
support for internal
organs
Function of Bone
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Movement
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Skeletal muscle
attached to bones use
the bones as levers to
move the body
Arrangement of
bones and joints
determine the
movements possible
Function of Bone

Protection
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Fused bones provide
a brain case that
protects this vital
tissue
Spinal cord is
surrounded by
vertebrae
Rib cage protects
vital organs
Function of Bones
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Mineral Storage
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Bone serves as a
mineral reservoir
Phosphate and
calcium ions can be
released into the
blood steam for
distribution
Deposition and
removal are ongoing
Function of Bones
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Blood cell formation
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Hematopoiesis occurs
within the red
marrow cavities of
the long bones
The yellow marrow
cavities are involved
in fat storage
CLASSIFICATION OF BONE
SECTION III
Classification of Bone:
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Bones vary in shape and size
The unique shape of each bone fulfills a
particular need
Bones are classified by their shape as
long, short, flat, or irregular bone
Bones differ in the distribution of
compact and spongy osseous tissues
Classification of Bones
Classification:
Long Bone
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Long bones have a
long shaft and two
distinct ends
Classification is
based on shape not
size
Compact bone on
exterior w/ spongy
on the interior
Classification:
Short Bones
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Short bones are
roughly cubelike
Thin compact bone
layer surrounding
spongy bone mass
Short bones are
often carpal, tarsal
and sesamoid bones
Classification:
Flat Bones
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Flat bones are
thin, flattened and
usually curved
Parallel layer of
compact bone with
spongy bone layer
between
Skull, sternum and
ribs are examples
Classification:
Irregular Bone
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Irregular bones don’t
fit into the previous
categories
Complicated shapes
Consist of spongy
bone with a thin layer
of compact
Examples are hip
bones & vertebrae
Gross Anatomy of Bones
SECTION IV
Gross
Anatomy

Landmarks
– Diaphysis
– Proximal
epiphysis
– Distal
epiphysis
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Membranes
– Periosteum
– Endosteum
Diaphysis
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Long tubular
diaphysis is the
shaft of the bone
Collar of compact
bone surrounds a
central medullary
or marrow cavity
In adults, cavity
contains fat
Epiphysis
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The epiphyses are
the ends of the
bone
The joint surface
of the epiphysis is
covered with
articular cartilage
Epiphyseal line
separate diaphysis
and epiphysis
Blood Vessels
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Unlike cartilage
bone is well
vascularized
Nutrient arteries
serve the diaphysis
The nutrient artery
runs inward to
supply the bone
marrow and the
spongy bony
Medullary cavity
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The interior of all bones
consists largely of
spongy bone
The very center of the
bone is an open or
marrow cavity
The cavity is filled with
yellow bone marrow
Membranes
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Periosteum covers
outer bone surfaces
except the ends of
the epiphysis
The membrane has
two sublayers
– Superficial layer
– Osteogenic layer
Membranes
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The superficial layer consists of dense
irregular connective tissue which resists
tension placed on a bone during bending
The osteogenic layer abuts the compact
bone and contains bone-depositing cells
called osteoblasts and osteoclasts that are
responsible for bone remodeling
Membranes
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During periods of bone growth or
deposition the osteogenic cells
differentiate into osteoblasts
Osteoblasts produce the bone tissue that
forms the circumferential lamellae that
encircle the perimeter of the bone
Membranes
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Periosteum is richly
supplied with nerves
and blood vessels
The periosteum is
supplied by
branches of the
nutrient artery and
epiphyseal vessels
Membranes
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The periosteum is
secured to the
underlying bone by
perforating fibers
(Sharpey’s fibers)
Thick bundles of
collagen fibers run
from the periosteum
into the bone matrix
Membranes
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Internal bone
structures are
covered by a thinner
connective tissue
membrane the
endosteum
It also contains the
osteoclasts and
osteoblasts necessary
for bone remodeling
Membranes
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The endosteum
covers the
trabeculae of
spongy bone
and lines the
central canals
of osteons
Short, Irregular and Flat Bones
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Bones consist of thin
layers of compact
bones over spongy
bone
No shaft, epiphysis or
marrow cavity
Spongy area between
is a diploe
Flat sandwich of bone
is common in bones of
skull
Bone Design and Stress
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The internal anatomy of each bone reflects
the stresses most commonly placed upon it
Bones are subjected to compressive forces in
weight bearing and tension forces when
muscle pulls upon them
Often weight bearing loads are applied off
center which threatened to bend the bone
Bone Design and Stress
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Bending
compresses the
bone on one side
and compresses it
on the other
Compression and
tension are greatest
at the external
surfaces of the
bone
Bone Design and Stress
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Compact bone
occurs at the
external surfaces to
resist these tension
and compression
forces
Internal bone
structures are not
subjected to these
forces and thus
spongy bone is
sufficient
Bone Design and Stress
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As there are only
limited tension and
compression forces
at the bone’s center
the hollow
medullary cavity
does not impact a
long bone’s weight
bearing capacity
Bone Design and Stress
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Spongy bone is not
a random network
of bone fragments
The trabeculae
align along stress
lines in an
organized patterns
of tiny struts that
provide internal
support for the
bone
Bone Markings
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Bones are shaped by the tissues that act
upon and around them
Bones display bulges, depressions and
holes which serve as sites of muscle,
ligament and tendon attachment, points
of articulation, or as conduits for blood
vessels and nerves
Projections from the bone surface include
heads, trochanters, spines, and others
Depressions include fossae, sinuses,
foramina, and grooves
Bone
Markings
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Tuberosity - a large
rounded projection
which may be
roughened
– tibial tuberosity
Bone Markings
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Crest - A narrow
ridge of bone;
usually prominent
– Crest of the ilium
Bone Markings
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Trochanter - A
very large, blunt,
irregularly shaped
process
– Greater trochanter
of femur
Bone Markings
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Line - Narrow
ridge of bone; less
prominent than a
crest
– Intertrochanteric
line
Bone Markings
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Tubercle - Small
rounded
projection or
process
– adductor tubercle
Bone Markings
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Epicondyle raised area on or
above a condyle
– medial epicondyle
of the humerous
Bone Markings
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Spine - A sharp,
slender, often
pointed projection
– Spinous process of
vertebrae
Bone Markings
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Head - Bony
expansion carried
on a narrow neck
– head of the
humerus
Bone Markings
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Facet - Smooth, nearly flat articular surface
– facet on transverse process of thoracic vertebrae
Facet
Bone Markings
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Condyle - Rounded
articular projection
– lateral condyle of
femur
Bone Markings
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Ramus - Armlike
bar of bone
– ramus of the pubis
Bone Markings
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Meatus - canal-like
passageway
– External auditory
meatus
Bone Markings
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Sinus - Cavity
within a bone,
filled with air and
lined with mucous
membrane
– nasal sinus
Bone Markings
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Fossa - Shallow,
basinlike
depression in a
bone often serving
as an articular
surface
– Olecranon fossa
Bone Markings
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Groove - a
narrow furrow in
the surface of the
bone
– radial groove
Bone Markings
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Fissure - Narrow,
slitlike opening
Bone Markings
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Foramen - Round or oval opeing through a
bone
– Foramen magnum
Compact Bone
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Compact bone appears very dense
It actually contains canals and passageways
that provide access for nerves, blood vessels,
and lymphatic ducts
The structural unit of compact bone is the
osteon or Haversian system
Each osteon is an elongated cylinder
running parallel to the long axis of the bone
Functinally each osteon represents a weight
bearing pillar
Compact bone
Compact Bone
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Structurally, an osteon is a group of
concentric rings of bone tissue surrounding
a central canal
Each of the concentric rings called lamella
is a layer of bone matrix in which the
collagen fibers and mineral crystals align
and run in a single direction
Fibers of adjacent lamella run in roughly
opposite direction
Compact bone
Compact bone
An Osteon
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Each osteon is a
group of hollow
tubes of bone
matrix
Each matrix tube
contain lamella
Collagen fibers in
each layer run in
opposite directions
Orientation resists
torsion stresses
Compact Bone
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The alternating pattern of lamella
orientation is optimal for withstanding
torsion, stresses
The lamella of bone also inhibit crack
propagation
When a crack reaches the edge of a lamella,
the forces causing the crack are dispersed
around lamellar boundaries, thus
preventing the crack from progressing into
deeper parts of the bone and causing
fracture
An Osteon
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Running through
the core of each
osteon is the
central or
Haversian canal
The canal contains
small blood vessels
that supply the
cells of the osteon
Central or Haversian Canal
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The canal is
lined by
endosteum
The canal
contains the
blood supply
for the osteon
Perforating (Volkmann’s) Canal
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Canals lie at
right angles to
long axis of
bone
Connect the
vascular
supply of the
periosteum to
those of the
central canal
and medullary
cavity
Compact Bone
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Osteocytes are the
mature bone cells
occupying the
small spaces in the
solid matrix called
lacuna
Thin tubes called
canaliculi run
through the matrix
connecting
Compact Bone
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Osteocytes occupy
small cavities or
lacuna at the
junctions of
lamella
Fine canals called
canaliculi connect
the lacuna to each
other and to the
central canal
Canaliculi tie all
the osteocytes in an
osteon together
Compact Bone
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Canaliculi run through the matrix
connecting neighboring lacunae to one
another and to the nearest capillaries such
as those in the central canal
Within the canaliculi, the extensions of
neighboring osteocytes touch each other and
form gap junctions
Compact Bone
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Gap junctions
allow nutrients
diffusing from the
capillaries to cross
these junctions
Nutrients are then
passed from one
osteocyte to the
next
Compact Bone
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The passage of nutrients through gap
junctions occurs throughout an entire
osteon
This direct transfer from cell to cell is the
only way to supply osteocytes with nutrients
as the intervening bone matrix is too solid
and impermeable to act as a diffusion
medium
Compact Bone
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Osteocytes remain in the matrix they have
secreted
Live cells appear to be needed to maintain
the matrix
Loss of osteocytes from the matrix results
resorbtion of the matrix
Compact Bone
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Not all lamellae in
compact bone
occur in osteons
Interstitial lamellae
are incomplete
lamellae lying
between the
cylindrical osteons
These represent
remnants old
osteons cut by bone
remodeling
Spongy Bone


Spongy bone
occurs at the
ends of long
bones and
surrounding the
medullary cavity
It is less dense
and complex
than compact
bone
Spongy Bone
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Trabeculae are the
dominate feature
Trabeculae contain
irregularly arranged
lamallae and osteocytes interconnected
by canaliculi
There are no osteons
present
Osteocytes receive
nutrients from
capillaries in
endosteum
Spongy Bone
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Trabeculae align
along lines of stress
Function as struts of
bone
Chemical Composition of Bone

The organic components of bone are:
–
–
–
–
Osteoblasts
Osteocytes
Osteoclasts
Osteoid
(bud cells)
(mature cells)
(large cells which resorb matrix)
(organic part of the matrix)
• Osteoid makes up 1/3 of the matrix
• Includes proteogylcans, glycoproteins, & collagen
• These components, particularly collagen contribute
to the flexibility and tensile strength of bone to
resist stretching and twisting
Chemical Composition of Bone
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The inorganic components of bone (65%
by mass) consist of hydroxyapatites or
mineral salts, largely calcium phosphate
Tiny crystals of calcium salts are deposited
in and around the collagen fibers of the
extracellular matrix
The crystals are exceptionally hard and
resist compression
Organic and inorganic components of
matrix allows a bone to be strong but not
brittle
Bone Development

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Osteogenesis and ossification refer to the
process of bone formation
Osteogeneis begins in the embryo and
continues until adulthood
Remodeling is bone resorption and
deposition in response to stress and
repair of bone
Bone Development


Before week 8 the skeleton of the human
embryo is made entirely from hyaline
cartilage and mesenchyme membranes
At 8 weeks bone begins to appear and
eventually replaces most cartilage and
mesenchymal membranes
Bone Development
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Bones that develop from mesenchymal
membranes are called membrane bones
Membrane bones develop from a fibrous
membrane in a process called intramembranous ossification
Other bones develop as hyaline cartilage
initially, which is replaced through a
process called endochondrial ossification
These are referred to as endochondrial
bones or cartilage replacement bones
Intramembranous Ossification
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Membrane bones form directly from
mesenchyme without being modeled in
cartilage
All bones of the skull (except a few at the
base of skull) are membrane bones
The clavicles are also membrane bones
Note that most of these bones are flat
bones
Intramembranous Ossification
Intramembranous Ossification
Intramembranous Ossification
Intramembranous Ossification
Endochondral Ossification
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Most bones (except clavicles and most
skull bones) form by the process of
endochondral ossification
The bones are first modeled in hyaline
cartilage, which is then gradually
replaced by bone tissue
This process uses hyaline cartilage
“bones” as the pattern for bone
construction
Endochondral Ossification
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Endochondral ossification begins late in
the second month of development and
continues into early adulthood when the
skeleton is fully ossified
In endochondral ossification the cartilage
model of the bone is replaced by bone
Growing endochondral bones increase in
length and in width
Endochondral Ossification
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Cartilage bones are surrounded by a
perichondrium
At the 8th week of development, the
perichondrium (fibrous connective tissue
layer) becomes infiltrated by blood
vessels converting it to a vascularized,
bone forming periosteum
The increase in nutrition enables the
mesenchyme cells to differentiate into
osteoblasts that form a collar of bone
Endochondrial Ossification
Endochondral Ossification


Formation of a
bone collar around
diaphysis of
cartilage model
Osteoblasts of the
new periosteum
secrete osteoid
against the hyaline
cartilage along the
length of the
diaphysis
Endochondral Ossification


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
Cartilage in the
center of the
diaphysis calcifies
Calcification of
cartilage blocks
nutrients and
chondrocytes die
Matrix deteriorates
and cavities develop
Bone is stabilized
by collar; while new
cartilage adds to
bone growth
Endochondral Ossification



Invasion of the
internal cavities by
the periosteal bud
Bud contains
nutrient artery &
vein, lymphatics,
nerve fibers, red
marrow elements,
osteoblasts and
osteoclasts
Spongy bone forms
Endochondral Ossification



Formation of the
medullary cavity as
ossification continues
Secondary
ossification centers
form in epiphyses
Cartilage in
epiphyses calcifies
and deteriorates
opening cavities for
entry of periosteal
bud
Endochondral Ossification




Ossification of the
epiphyses
Hyaline cartilage
remains only at
epiphyseal plates
Epiphyseal plates
promote growth
along long axis
Ossification chases
cartilage formation
along length of
shaft
Endochondral Ossification

After the secondary ossification sites have
appeared and epiphyses have largely
ossified, hyaline cartilage remains on
– Epiphyseal surfaces where it forms articular
cartilages
– Between the diaphysis and the epiphysis
where it forms the epiphyseal plates
– The epiphyseal plates or growth plates are
responsible for lengthening of bones during
the two decades following birth
Long Bone Growth

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

Cells in the epiphyseal plate
undergo rapid cell mitosis
pushing epiphysis away from
diaphysis
Older cells enlarge, matrix
becomes calcified
Chondrocytes die and their
matrix deteriorates
Calcified cartilage is covered
by bone matrix secreted by
osteoblasts to form spongy
bone
Epiphyseal Growth Areas


In the epiphysis of
the fetus and the
epiphyseal plates are
organized to allow
bones to grow
quickly & efficiently
The cartilage cells
nearest the epiphysis
(quiescent zone) are
relatively inactive
Epiphyseal Growth Areas



The cartilage cells
form tall columns in
the proliferation zone
The rapid division of
chondroblasts push
the epiphysis away
from the diaphysis
The growth here
lengthens the entire
long bong
Epiphyseal Growth Areas


Older cartilage cells
that are deeper in the
column in the
(hypertrophic zone)
enlarge and signal
the surrounding
matrix to calcify
In the calcification or
osteogenic zone the
matrix becomes
calcified and the
chondrocytes die
Epiphyseal Growth Areas



The process of
ossification leaves
long spicules
(trabeculae) of
calcified cartilage on
the diaphysis side
The spicules are then
covered with bone
tissue by osteoblasts
Osteoclasts complete
the remodeling of the
bone
Postnatal Bone Growth



During childhood and adolescence bone
growth occurs entirely by growth at the
epiphyseal plates
In growing bones cartilage is replaced
with bone tissue on the diaphysis side
about as quickly as it grows
The epiphyseal plate remains a constant
thickness while the overall length of the
bone increases
Postnatal Bone Growth




As the end adolescence approaches, the
chondroblasts in the epiphyseal plate
divide less often
The epiphyseal plates become thinner,
eventually exhausting their supply of
mitotically active catilage cells
The cartilage stops growing and is
replaced by bone tissue
The epiphyseal plate fuses and growth is
done (18 female, 21 male)
Postnatal Bone Growth




Bones grow in width by appositional
growth
Osteoblasts in the periosteum add bone
tissue to the external surface of the
diaphysis
Osteoclasts in the endosteum remove
bone from the internal surface of the
diaphysis wall
These two processes occur at roughly the
same rate
Postnatal Bone Growth


Other types of endochondial bones grow
in slightly different patterns
Bone growth is regulated by several
hormones
– Pituitary simulates growth at plates
– Thyroid regulates growth to ensure that the
skeleton retains proper proportions
– Sex hormones influence growth at adolescent
growth spurts
Growth and Remodeling
Bone Remodeling




Bone is dynamic and active tissue
Long bone growth is accompanied by
almost continuous remodeling in order to
maintain proper proportions
Large amounts of bone matrix and
thousands of osteocytes are being
continually removed and replaced
The small scale architecture of bones
changes constantly
Bone Remodeling



The spongy bone of the skeleton is
replaced every 3 years
The compact bone is replaced every 10
years
The remodeling process is not uniform as
some parts experiencing more stress are
replaced at a faster rate (every 5-6
months) while other areas change more
slowly
Bone Remodeling



Bone remodeling involves both bone
formation and resorption
Remodeling occurs at the periosteal and
endosteal sufaces
Bone formation is done by osteoblasts
and bone resorption is done by
osteoclasts
Bone Remodeling
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Bone remodeling is coordinated by cohorts of
adjacent osteoclasts called remodeling units
Osteoclasts crawl along the bone surfaces digging
pits as they break down bone surfaces
Bone Remodeling
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Osteoclasts are
large cells with
many nuclei
Their plasma
membrane is
highly folded or
ruffled
Bone Remodeling

The ruffled plasma
membrane forms a
tight seal against
the bone and HCL
dissolves the
mineral portion of
the matrix
Bone Remodeling
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Osteoclasts release calcium ions (Ca2+)
and phosphate ions (PO43-) that enters the
tissue fluid and the bloodstream
Lysosomal enzymes are also released by
the osteoclasts and digest the organic part
of the bone matrix
Finally, osteoclasts take up collagen and
dead osteocytes by phagocytosis
Bone Remodeling

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Bone deposition is accomplished by osteoblasts
Osteoblasts lay organic osteoid on bone surfaces
and calcium salts crystalize within this osteoid
Bone Remodeling


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Bone forming osteoblasts form from
mesenchyme-like stem cells located in the
periosteum, endosteum, and the
connective tissue of nearby bone marrow
Osteoclasts form in bone marrow from
immature blood cells called
hematopoietic stem cells
Many of these stem cells fuse together to
form each osteoclast, thus their
multinucleate structure
Bone Remodeling

Bone of the skeleton are continually
remodeled for 2 reasons
– Bone remodeling helps maintain constant
concentrations of Ca2+ and PO43- in bodily
fluids
– Bones are remodeled in response to the
mechanical stress it experiences
• Osteons of compact bone and the trabeculae of
spongy bone are constantly replaced by new
osteons and trabeculae that are more precisely
aligned with newly experienced compressive and
tensile forces
Bone Anatomy and Stress

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Wolff’s law holds
that a bone grows
or remodels in
response to the
forces which act
upon it
Changes in bone
density in response
to exercise
Tension and
compression forces
must balance
Healing of a Bone Fracture
Common Types of Fractures
Common Types of Fractures
Common Types of Fractures