88
UNIT 2
Basic Tissues
D. Cui /T. Yang
D. Cui /T. Yang
Interstitial Growth
Chondrocyte in lacuna
Territorial matrix
Interterritorial matrix
Isogenous group
Chondroblast
Chondrogenic cell
Inner cellular layer
of the perichondrium
Outer fibrous layer
of the perichondrium
Appositional Growth
Figure 5-7.
A representation of cartilage growth.
Cartilage grows by either
appositional
or
interstitial growth
or by
both
. The growth process is continuous and involves mitosis and the
deposition of additional matrix.
Appositional growth
begins with the
chondrogenic cells
in the
perichondrium
. These chondrogenic cells
differentiate into
chondroblasts
, which are also called
young chondrocytes
. Chondroblasts start to elaborate a new layer of matrix at the
surface (periphery) region of the cartilage near the perichondrium. Cartilage grows mostly by appositional growth.
Interstitial growth
occurs during the early stages of cartilage formation. The growth begins with the cell division of preexisting chondrocytes (mature chon-
droblasts which are surrounded by territorial matrix). Interstitial growth increases the tissue size by expanding the cartilage matrix from
within the cartilage mass. This type of growth is indicated by the presence of
isogenous groups
in most cartilage, though sometimes the
chondrocytes are arranged in small groups in parallel columns and rows. Articular cartilage lacks a perichondrium, so it enlarges only by
interstitial growth. Interstitial growth serves to lengthen the bone such as in the epiphyseal plates of long bones (see Fig. 5-12B).
SYNOPSIS 5-1
Functions of Cartilage
Hyaline cartilage
Serves as the
cartilage model
for the formation of bones during bone development.
Participates in bone-lengthening growth by increasing chondrocyte size and numbers during bone development
(
endochondral ossi± cation
).
Enables free movement by forming smooth surfaces that work with lubricating fl uid (
synovial fl uid
) in articular
cartilage
of the joints.
Provides support and framework for airways in the respiratory tract.
Elastic cartilage
Provides elastic but stiff framework for pinna and allows it to return to its former shape after stretching.
Provides elastic support for auditory canals and tube; helps to maintain structural shape.
Provides a ± rm and elastic support for the epiglottis and larynx; helps to maintain rigid structure and fl
exibility.
Fibrocartilage
Provides tensile strength for connections between the bones such as the pubic symphysis.
Provides cushioning and resistance between vertebrae, enabling the spinal column to endure great pressure.
SYNOPSIS 5-2
Special Features of Cartilage
The
function
is to provide ± rm support with variable fl
exibility depending on its location.
The extracellular matrix is
nonmineralized
and consists of ±
brillar proteins (collagen) and ground substance (GAGs,
proteoglycans, and glycoproteins).
The extracellular matrix is produced by
chondroblasts
and
chondrocytes
.
Cartilage grows by both
interstitial
and
appositional
mechanisms.
It is an
avascular tissue
; the nutrients are supplied through matrix diffusion.
The
perichondrium
provides the nearest blood supply to the cartilage.
Vitamins A
,
D
, and
C
are necessary for cartilage growth and matrix formation.
Cartilage Growth
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