Cartilage
Dr. Ahmad Al-Taib
Written by:
Albara Marwa,, Abo Malik
Group A leader
What is cartilage?
• It is a special type of connective tissue with
a firm extracellular matrix.
Location
• Cartilage is found in:
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Respiratory tract
External ear
Intervertebral disc
Articular surface of bones (in joints)
Skeleton of fetus
Components
• Cartilage consists of three components:
– Cells
– Matrix (between the cells)
– Perichondrium (outer layer)
Cartilage cells
• Cartilage contains three types of cells:
– Chondrogenic cells
– Chondroblast
– chondrocyte
1. Chondrogenic cells
• Originate from mesenchymal cells
• Spindle shaped cells with oval nuclei
• Found in the perichondrium
• Differentiate into chondroblasts
(Differentiation of cells does not include cell
division but only a change in structure)
2.Chondroblasts
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Basophilic flat cells with flat nuclei
Protein-secreting cells
Secrete cartilage matrix
Found in the perichondrium
Originate from chondrogenic cells
3. Chondrocyte
• Each chondroblast secretes the matrix & becomes
a chondrocyte with a large rounded nucleus.
• The chondrocyte is the mature cartilage cell
which also secretes matrix.
• Each chondrocyte is situated in a small space
called a lacuna surrounded by the matrix.
• The chondrocyte can divide in the lacuna
• There is no connection between the lacunae.
Cartilage Matrix
• The matrix is an avascular extracellular
material secreted by chondroblast &
chondrocyte.
• Cartilage matrix consists of:
– Fibers: collagen type I or type II or elastic
fibers.
– Ground substance: glycoproteins &
chondroitin sulphate.
Perichondrium
• A dense vascular connective tissue on the
surface of cartilage.
• It consists of:
– Outer fibrous layer of dens CT (Type I
collagen).
– Inner cellular layer of chondrogenic cells &
chondroblast.
• Its function is growth of cartilage
Types of cartilage
• There are three types according to the
fibers in the matrix:
– Hyaline cartilage
– Elastic cartilage
– Fibrocartilage
Similarities between types of
cartilage
• All types have chondrocyte in lacunae.
• All types have avascular matrix.
• All types have perichondrium EXCEPT:
– Fibrocartilage
– Articular cartilage
Hyaline cartilage
• Found in:
– Respiratory tract
– Articular cartilage
• Chondrocytes divide and form small groups
called isogenous group.
• Collagen type II in a basophilic matrix, but the
collagen is not visible with the L.M.
• The matrix is more basophilic near the
chondrocyte.
• Articular cartilage lacks perichondrium and it
receives nutrient from the synovial fluid
Elastic cartilage
• More chondrocytes and less matrix than
hyaline cartilage.
• Many elastic fibers in the matrix and in the
perichondrium.
• Collagen type II is also present
• Examples: External ear & epiglottis.
• Elastin stain stains elastin black
Fibrocartilage
• Parallel bundles of acidophilic type I collagen
fibers in the matrix.
• (Note: Collagen type I is stronger than type II).
• Chondrocytes form parallel rows.
• Chondrocytes arise from fibroblasts.
• More fibers and less chondrocytes than that in
hyaline and elastic cartilage.
• No perichondrium
• Example: Intervertebral disc
Cartilage growth
• Cartilage arises from mesenchyme during
chondrogenesis
• Cartilage grows by two methods:
– Appositional growth : on surface from
perichondrium.
– Interstitial growth: deep in matrix.
Repair of cartilage
• Cartilage has a limited ability for repair.
• Injured cartilage is replaced by Connective
tissue.