Histology

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Dr. Sally Selim
Dr. Nadia El- Akabawy
 ILOs:
 General structure of cartilage.
 The 3 histological types of cartilage.
 The functional structure of each type.
What is cartilage?
 Cartilage is a strong, flexible
specialized connective tissue
that protects your joints and
bones.
 Cartilage acts as a shock
absorber throughout your body.
 Cartilage at the end of your
bones reduces friction and
prevents them from rubbing
together when using your joints.
General Features of Cartilage:
1-It resists mechanical stress and has variable degrees
of flexibilities.
2-Cartilage is surrounded by a membrane of vascular
connective tissue called perichondrium.
3-Cartilage has no blood vessels (avascular), no
lymphatics,and no nerve fibers.
4-Cartilage takes its nutrients by diffusion through the
matrix from the perichondrium (or from the synovial
fluid in articular cartilage).
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- Chondrogenic cells
- Chondroblast
- Chondrocyte
- Chondroclast
Matrix:
Fibers:
Cells:
- Collagen Fs.
- Elastic Fs.
- Glycoproteins
- Proteoglycans
Perichondrium:
-The perichondrium covers all the surfaces of the cartilage except the
articular cartilages of the joints.
- Formed of two layers:
a) Outer fibrous:Collagen fibers,blood vessels, nerves and fibroblasts
b) Inner cellular: Chondrogenic cells and chondroblasts that secret matrix
and collagen fibers
Function:
1. Supply nutrition
2. Form new cartilage cells during growth
3. Attachment of skeletal muscles
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Cells
 Chondrogenic cells:
Origin: bone marrow derived MSCs.
Site: in the inner cellular layer of
perichondrium.
L.M: They are spindle-shaped narrow cells.
Nucleus: oval and pale basophilic.
The cytoplasm: light basophilic.
E.M: They have free ribosomes, few
mitochondria, some RER and small Golgi
apparatus.
Function: divide and differentiate into
chondroblasts.
 Chondroblast:
Origin: from chondrogenic
cells.
Site: in the inner side of
perichondrium.
L.M: elliptic shape, the long
axis is parallel to the surface,
basophilic cytoplasm with
vesicular nucleus.
EM
1. The cytoplasm is rich in
organelles of protein
synthesis (ribosomes,
rough endoplasmic
reticulum, well developed
Golgi apparatus and
mitochondria).
2. The nucleus contains
more euchromatin.
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Function: play an important role in the formation
of cartilage.
•Development of cartilage:The primary function of the
chondroblast is the development of the cartilage.
Chondroblasts found in the inner layer of the perichondrium
mature to form chondrocytes, which form the cellular structure
of the cartilage tissue.
•Maintenance of cartilage: Chondroblast also helps maintain the
structure and strength of the cartilage tissue by producing
components of the ECM.
•Growth of cartilage: Chondroblasts carry out appositional
growth of the cartilage, i.e., thickening of cartilage tissue.
 Chondrocytes:
Origin: from chondroblast.
Site: in the cartilage matrix within
lacunae.
L.M: large rounded cells with dark
nucleus and pale basophilic cytoplasm.
Chondrocytes may also appear in
isogenous groups of up to eight cells.
Mitotic cell division of individual
chondral cells leads to cellular
grouping.
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During histological preparation,
chondrocytes and their matrix
shrink, which retracts the cells
from the capsule and produces its
irregular shape.
E.M: few ribosomes, RER,
mitochondria, lipid droplets and
heterochromatic nucleus.
Function:
•Maintenance of cartilage:
Chondrocytes helps maintain the
structure and strength of the
cartilage tissue by preserving
components of the ECM.
•Interstitial Growth of cartilage:
Chondrocytes divide inside their
lacunae resulting in growth of the
cartilage at the center.
 Chondroclast:
Origin: bone marrow
hematopoietic progenitors that
give rise to monocytes in
peripheral blood.
Site: on the deep surface of
resorbed hyaline cartilage.
L.M: multinucleated cells like
osteoclast.
E.M: like osteoclast.
Function: Chondroclasts
form on calcified cartilage to
resorb mineralized cartilage
matrix during endochondral
ossification and pathological
conditions of cartilage
resorption as in arthritic
conditions.
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Chondroblast Chondrocytes
Immature developmental cartilage
cells that are involved in the
development of the cartilage tissue
Mature cartilage cells that function
to maintain the cartilage structure.
actively produce the component of
the ECM.
secrete ECM and are embedded in
it.
originate from mesenchymal
chondrogenic cells.
originate from the chondroblasts.
Appositional growth of the cartilage
by chondroblasts
Interstitial growth of the cartilage
by chondrocytes
Main function is to produce
chondrocytes and components of
the ECM
Primarily, to maintain the structure
of the cartilage and ECM
Fibers
Cartilage Fibers:
The fibers are either solely collagenous or a combination of
elastic and collagenous, depending on the cartilage type.
 Elastic fibers
in elastic cartilage.
 Collagen fibers type I
in fibrocartilage.
 Collagen fibers type II
in hyaline and elastic cartilage.
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Ground
Substance
( Matrix )
Matrix: - Matrix is the avascular extracellular
material secreted by chondroblast &
chondrocyte.
- More than 95% of cartilage volume
consists of extracellular matrix
(ECM).
- The ECM in cartilage is solid and
firm but also somewhat pliable,
which accounts for its resilience.
- Because there is no vascular
network within cartilage, the
composition of the ECM is crucial to
the survival of the chondrocytes.
 The main matrix components are
proteoglycans and glycoproteins;
- Proteoglycans: mostly sulfated
glycosaminoglycans responsible for matrix
basophilic staining. The main
glycosaminoglycans are chondroitin sulfate.
- Glycoprotein: adhesive proteins adhering
matrix to chondrocytes.
 The matrix closely
surrounding the
chondrocytes are
named capsular
territorial matrix, the
matrix in between
chondrocytes are
named interterritorial
matrix.
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Interstitial growth :
 Young chondrocytes divide
inside their lacunae resulting in
growth of the cartilage at the
center and increase in length.
 Occurs deep in matrix.
Appositional growth :
 Mitotic division of
chondroblasts adds more
layers to the surface of the
cartilage resulting in increase
in width
 Occurs on the perichondrium.
# Cartilage growth: Cartilage grows by two methods:
# Cartilage repair :
 Cartilage has a limited ability for repair.
 Injured cartilage is replaced by Connective tissue.
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# Cartilage Histological Types : according to the type of fibers;
 Hyaline Cartilage.
 Elastic Cartilage.
 Fibrocartilage.
1- Hyaline Cartilage:
Site:
- Costal cartilage.
- Articular cartilage.
- Epiphyseal cartilage
(Ends of long bone for bone growth).
- Fetal skeleton
(Mold for future bone formation).
- Laryngeal skeleton
(Cricoid and thyroid cartilages).
- Nasal cartilage.
Structure = Matrix + Fibers + Cells
 Hyaline cartilage is the most common of
the three types of cartilage.
 In fresh state, it is homogeneous and
semi-transparent, hence its name, as
hyalos is greek for glassy.
 As cartilage is avascular, it receives
nutrients by diffusion from capillaries
originating from the perichondrium.
 Perichondrium is a layer of dense
connective tissue that surrounds all
hyaline cartilage, except in the articular
cartilage of movable joints.
 The Matrix contains mainly fine collagen II
fibrils.
 The Matrix is clear basophilic as the
refractive index of the amorphous ground
substance is the same as that for collagen
II therefore, collagen can not be seen in
common H&E sections.
 Basophilia is due to the high
concentration of the negatively- charged
sulfate groups making it appear intensely
basophilic under H&E. There is masking of
the acidophilic collagen fibers by the high
concentration of the glycosaminoglycans
in the ground substance.
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Hyaline Cartilage
Cells:
- Chondrogenic cells:
Found mainly in the inner
chondrogenic layer of the
perichondrium.
- Chondroblasts:
Found superficially under
the perichondrium.
- Chondrocytes:
They are located in tiny
spaces within the cartilage
matrix known as lacunae.
2- Elastic Cartilage:
Site:
- Auricle and Auditory tube.
- Cuneiform Cartilage.
- Epiglottis and External auditory meatus.
Structure = Matrix +
Fibers + Cells
 Elastic cartilage is resilient, easily
returning to its original shape after
bending or distortion so, it present in
areas where elastic recoil is needed.
 In fresh state, it is yellow in color.
 The Matrix is rich in dense,
interwoven network of elastic fibers
embedded in a small amount of
amorphous extracellular ground
substance plus collagen II fibrils.
 Elastic fibers stain pink in
Hematoxylin and Eosin, black in
Verhoeff's Van Gieson stain, and
brown in Orcein.
3- Fibrocartilage:
Site:
- Symphysis pubis.
- Annulus fibrosis of
intervertebral discs.
- At points of tendons’
attachment to bone.
- Tempo- mandibular joint.
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 In fresh state, fibrocartilage
is white in color.
 Fibrocartilage is the
strongest and least flexible
of the three types.
 Its primary role is to provide
reinforcement at weight-
bearing areas, It acts more
like a shock absorber.
Structure = Matrix + Fibers + Cells  Fibrocartilage has a dense arrangement of type I collagen fibers that
are arranged in an orderly manner.
 Numerous chondrocytes are located within their lacunae and are
spaced between the acidophilic regular collagen bundles.
 No perichondrium.
# Clinical note:
Disc prolapse;
- Disk herniation occurs
when the fibrocartilage
surrounding the
intervertebral disk
ruptures, releasing the
nucleus pulposus.
- The resultant pressure on
spinal nerve roots may
cause pain and damage the
surrounding nerves.
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Articular cartilage lacks perichondrium and it receives nutrient
from the synovial fluid
The matrix is more basophilic near the chondrocyte.
Collagen type II in a basophilic matrix, but the collagen is not
visible with the L.M.
Chondrocytes divide and form small groups called isogenous
group.
found in:
- Respiratory tract - Articular cartilage
Hyaline cartilage
Elastin stain stains elastic fibers black
Collagen type II is also present.
Many elastic fibers in the matrix and in perichondrium.
More chondrocytes and less matrix than hyaline cartilage.
found in:
- External ear - Epiglottis
Elastic cartilage
No perichondrium
Collagen type I present in parallel acidophilic
bundles. (Note: Collagen type I is stronger than type II)
More fibers and less chondrocytes than that in hyaline
and elastic cartilage.
Chondrocytes arise from fibroblasts and form parallel rows.
found in: - Intervertebral discs
Fibrocartilage
All types have chondrocytes in lacunae.
All types have avascular matrix.
All types have perichondrium-->>
EXCEPT: Fibrocartilage/ Articular cartilage
Similarities between types of cartilage
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