CARTILAGE AND BONE
Similarities
•Living cells embedded in a matrix produced by themselves
•Cells occupy spaces in the matrix called lacunae
•Both develop from mesenchyme
•Both are covered by connective tissue
Differences
•Nutrition of cells
•Growth
Histological preparation of hyalin cartilage
territorial matrix
isogenous group
perichondrium
Chondroblastsappositional growth
cell
Chondrocytes interstitial growth
matrix
lacunae
Several growth factors : FGF, IGF, TGF-b and growth hormone
influence cartilage growth
Condrocytes inside hyaline cartilage
territorial matrix
Isogenous group
matrix
EM of chondrocyte and surrounding matrix
proteoglycans
territorial matrix
collagen type II fibrils
piokl
Proteoglycan
aggregate
Cartilage matrix content
• Water ≈ 70%
• Organic components ≈ 30% (Collagen type II
≈ 40% and Proteoglycans ≈ 60%)
• As a result the matrix has a gel-like strucure
that allows nutrition by diffusion and provides
flexibility and mechanical resiliance
• It also makes possible formation of
isogenous groups by division of
chondrocytes into the matrix and for
interstitial growth of cartilage from inside
Types of cartilage
•
•
•
•
•
All of them contain collagen type II plus:
Hyalin cartilage
---Elastic cartilage
elastic fibers
Articular cartilage
collagen type I
Fibrocartilage
collagen type I
Elastic cartilage
perichondrium
elastic fiber
Articular cartilage
no perichondrium !
synovial cavity
articular cartilage
bone
bone marrow
Fibrocartilage
dense connective tissue
collagen type I fibres
rows of chondrocytes
Found around nucleus pulposus of intervertebral disks.
Again, no perichondrium !
Poor regeneration of cartilage
•Except in young chidren, damaged cartilage
regenerates with difficulties by activation of
perichondrium.
•If damage is extensive, perichondrium produces
a scar of dense connective tissue
BONE
Bone
Bone
Longitudinal section of adult long bone
Bone classification
trabeculae/spicules
cancelous/trabecular/spongy
compact/cortical
Blood vessels in a
system of Haversian
canals interconnected
with Volkman’s canals
0steon - complex of
concentric lamellae of
bone surrounding a
Haversian canal
Cementing substance
Interstitial lamellae
Inner circumferential
lamellae
Outer circumferential
lamellae
endosteum
periosteum
Thin section of
calcified bone
Osteon with
Haversian canal
Interstitial lamellae
Lacunae of osteocytes
Cement line
Histological preparation of decalcified bone
Osteons with Haversian canals
Volkman’s canal
Inner circumferential lamellae
Bone marrow
Primary, immature or woven bone (decalcified preparation)
Spicule/trabecular (~0.2 mm)
Beginning of formation of osteons,
but well defined lamellae are not yet formed
CELLS OF BONE
Mesenchymal cells
differentiating into
osteoblasts
Capillary
Not calcified bone matrix
osteoid
Osteocytes in
lacunae with
their processes
interconnected
Calcified bone
matrix is
penetrated by
canaliculi
Calcification/mineralization of
of bone matrix
• Inorganic matter is ≈ 50% of the dry weight of bone
matrix mainly in form of hydroxyapatite crystals Ca10(PO4)6(OH)2
• Initial mineralization in woven bone or cartilage by
matrix vesicles deposited by osteobalsts and
chondrocytes and enriched in alkaline phosphatase
and acidic phospholipids
• Mineralization front - mineralization of matrix
synthesized at already calcified mature bone surface
• Deficiency of Ca and vitamin D negatively influence
normal calcification process
osteocytes
canaliculi
calcified bone matrix
osteoclast
blood vessel
flat/resting osteoblasts
ruffled border
clear/adhesion zone
Howship’s lacunae
osteoblasts making
new bone
Remodeling
Bone turnover and skeletal
homeostasis
In a young adult ≈ 30% of
the total skeletal mass is
renewed every year by
remodeling in a balanced
fashion
activation of osteoclasts
Parathyroid hormone
inhibition of osteoclasts
Calcitonin
Shfting the balance
between bone formationCalcification of new bone and surface recovery
and bone resorbtion osteoporosis, osteopetrosis
activation of osteoblasts
osteoid
FORMATION OF HAVERSIAN CANAL
FORM ATION OF
HAVERSIAN CANAL
Activation of osteoclasts
Second concentric layer
First concentric layer
RESORBTION
Inhibition of osteoclasts
REVERSAL PHASE
FORM ATION
RESTING PHASE
Activation of osteoblasts
Intramembranous bone formation
New bone spicule/trabecular starts to
grow
Calcified matrix
osteoid
Process of remodeling starts
Osteoblasts start to
produce noncalcified
bone
Activation of mesenchymal
cells to turn
into
matrix (osteoid)
osteoblasts
Intramembranous formation of bones of the skull
Active osteoblasts producing osteoid
Calcified matrix
New bone spicules/trabeculae growing
Intramembranous bone formation
active osteoblasts producing osteoid
osteoid
osteocytes locked in bone matrix
resting osteoblasts
1. Starting with cartilage model
Endochondral
bone formation
4.2.Invasion
of osteoclasts
followedatby
blood
vessels
and osteogenic cells
Formation
of bony collar
the
middle
of diaphysis
5. Beginning of new bone synthesis over the calcified cartilage matrix
6.
of primary
center offollowed
ossification
3. Formation
Hypertrophy
of chondrocytes
by calcification
7.
Remodeling
and
growth
of their
marix and
their
death
8. Later a secondary center of ossification appears in the epiphyses
that is separated from the primary center by
growth plate of cartilage
Starting with cartilage model
Hypertrophy and degeneration of chondrocytes
Bony collar on the surface at the middle of
diaphysis formed by intramembranous bone
formation
Beginning of formation of primary center of ossification
Closer look at this area next
Propagation of the
process of primary
ossification followed
by remodeling of the
newly formed bone
trabeculae
At the same time
formation of bony
collar also continues
by Intramembranous
bone formation
Columns of dividing chondrocytes interstitial growth
Hypertrophy of chondrocytes
Calcification of cartilage matrix
and death of chondrocytes
Invasion of blood vessels and
osteogenic cells and beginning of
bone formation over calcified
cartilage matrix
Remodeling starts
Formation of secondary center of ossification
Secondary center of ossification
Epiphysis
Metaphysis
Growth/epiphysial plate
Advancing of primary ossification
Diaphysis
Endochondral bone formation
1. Starting
with
model
2.
Formation
of cartilage
bony collar
on the surface at the middle of
diaphysis
3. Hypertrophy and degeneration of chondrocytes
and calcification of their marix
4. Invasion of osteoclasts followed by blood
vessels and osteogenic cells
5. Beginning of new bone synthesis over the
calcified cartilage matrix
6. Formation of primary center of ossification
7. Remodeling and growth
8. Later a secondary center of ossification appears in the
epiphysis