Cartilage is a type of dense
connective tissue. It is composed of specialized cells
called chondrocytes that produce a large amount of extracellular
matrix composed of collagen fibers, abundant ground substance
rich in proteoglycan, and elastin fibers. Cartilage is
classified in three types, elastic cartilage, hyaline
cartilage and fibrocartilage, which differ in the relative
amounts of these three main components.
Cartilage is found in many areas in the body including
the articular surface of the bones, the rib cage, the
ear, the nose, the bronchial tubes and the intervertebral
discs. Its mechanical properties are intermediate between
bone and dense connective tissue like tendon.
Unlike other connective tissues, cartilage does not contain
blood vessels. The chondrocytes are fed by diffusion,
helped by the pumping action generated by compression
of the articular cartilage or flexion of the elastic cartilage.
Thus, compared to other connective tissues, cartilage
grows and repairs more slowly.
The three types of cartilage:
1.
Hyaline cartilage
Hyaline cartilage is a rather hard, translucent material
rich in collagen and proteoglycan. It covers the end of
bone to form the smooth articular surface of joints. It
is also found in the nose, the larynx and between the
ribs and the sternum. Bones grow via a hyaline cartilage
intermediate, a process called Endochondral ossification.
2.
Elastic cartilage
Elastic cartilage contains large amounts of elastic fibers
(elastin) scattered throughout the matrix. It is stiff
yet elastic, and is important to prevent tubular structures
from collapsing. Elastic cartilage is found in the pinna
of the ear, in tubular structures such as the auditory
(Eustachian) tubes and in the epiglottis.
3.
Fibrocartilage
Fibrocartilage is characterized by a dense network of
Type I collagen. It is a white, very tough material that
provides high tensile strength and support. It contains
more collagen and less proteoglycan than hyaline cartilage.
Thus, its properties are closer to those of tendons than
hyaline cartilage. It is present in areas most subject
to frequent stress like intervertebral discs, the symphysis
pubis and the attachments of certain tendons and ligaments.
