CHAPTER 5
Cartilage and Bone
81
providing for free movement, and is also involved in bone
formation and long bone growth (Figs. 5-3B and 5-12).
ELASTIC CARTILAGE
is similar to hyaline cartilage except
for its rich network of
elastic f
bers
, arranged in thick bundles
in the matrix. This type of cartilage has a
perichondrium
, as
does hyaline cartilage, and it also contains
type II collagen
in the matrix. The chondrocytes of elastic cartilage are more
abundant and larger than those of hyaline cartilage. Elastic car-
tilage is located in areas where elasticity and ±
rm support are
required, such as the epiglottis and larynx, auditory canal and
tube, and the pinna of the ear, which is able to recover its shape
after deformation (Fig. 5-5).
FIBROCARTILAGE
does not have a perichondrium. It has
type II collagen
, as do the other two types of cartilage. It is
characterized by thick, coarse bundles of
type I collagen
± bers
that alternate with parallel groups of columns (or rows) of
chondrocytes within the matrix. The chondrocytes of ± brocar-
tilage are smaller and much less numerous than in the other
two types of cartilage and are often arranged in columns or
rows. Because ± brocartilage has no perichondrium, its growth
depends on
interstitial growth
. Fibrocartilage is resistant to
tearing and compression, can accommodate great
pressure,
and is often found at connections between bones that do not
have an articular surface. It is found in areas where support and
tensile strength are required, such as intervertebral disks, the
pubic symphysis, and the insertions of tendons and ligaments
(Fig. 5-6).
Cartilage Growth
Cartilage grows by either
appositional
or
interstitial growth
or
both
. The growth process is prolonged and involves mitosis and
the deposition of additional matrix (Fig. 5-7). (1)
Appositional
growth
begins with the
chondrogenic cells
located in the per-
ichondrium. These chondrogenic cells differentiate into
chon-
droblasts
, also called
young chondrocytes
, and these cells start
to elaborate a new layer of matrix at the surface ( periphery)
region of the cartilage near the perichondrium. Most carti-
lage growth in the body is appositional growth. (2)
Interstitial
growth
occurs during the early stages of cartilage formation
in most types of cartilage. It begins with the cell division of
preexisting chondrocytes
(mature chondroblasts surrounded by
territorial matrix). Interstitial growth increases the tissue size
by expanding the cartilage matrix from within. Fibrocartilage
lacks a perichondrium, so it grows only by interstitial growth.
In the epiphyseal plates of long bones, interstitial growth serves
to lengthen the bone.
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