Organization of the Body
, the predominant cell type in growing carti-
lage, produce new matrix until the skeleton stops growing at the
end of adolescence. Te ﬁrmness of the cartilage matrix prevents
the cells from becoming widely separated, so
mature cartilage cells, are typically found in small groups within
Because cartilage is avascular and aging cartilage cells lose their
ability to divide, injured cartilages heal slowly. Tis phenom-
enon is excruciatingly familiar to those who have experienced
sports injuries. During later life, cartilages tend to calcify or
even ossify (become bony). In such cases, the chondrocytes are
poorly nourished and die.
Tere are three varieties of cartilage:
, each dominated by a particular
the most abundant cartilage in the body. Although it contains
large numbers of collagen ﬁbers, they are not apparent and the
matrix appears glassy (
glass, transparent) blue-white
when viewed by the unaided eye. Chondrocytes account for
only 1–10% of the cartilage volume (Figure 4.8g).
Hyaline cartilage provides ﬁrm support with some pliability.
It covers the ends of long bones as
springy pads that absorb compression at joints. Hyaline carti-
lage also supports the tip of the nose, connects the ribs to the
sternum, and supports most of the respiratory system passages.
Most of the embryonic skeleton consists of hyaline cartilage be-
fore bone forms. Skeletal hyaline cartilage persists during child-
hood as the
e-ul), actively growing
regions near the ends of long bones.
(Figure 4.8h) is
nearly identical to hyaline cartilage. However, elastic cartilage has
many more elastic ﬁbers. Found where strength and exceptional
stretchability are needed, elastic cartilage forms the “skeletons” of
the external ear (the pinna) and the epiglottis (the ﬂap that covers
the opening to the respiratory passageway when we swallow).
is intermediate be-
tween hyaline cartilage and dense regular connective tissues. Its
rows of chondrocytes (a cartilage feature) alternate with rows of
thick collagen ﬁbers (characteristic of dense regular connective
tissue) (Figure 4.8i). Because it is compressible and resists ten-
sion well, ﬁbrocartilage is found where strong support and the
ability to withstand heavy pressure are required: for example,
the intervertebral discs (resilient cushions between the bony
vertebrae) and the spongy cartilages of the knee (menisci) (see
Figure 6.1, p. 175).
Connective tissue proper: dense connective tissue, elastic
Dense regular connective tissue
containing a high proportion of elastic fibers.
Allows tissue to recoil after
stretching; maintains pulsatile flow of blood
through arteries; aids passive recoil of lungs
Walls of large arteries; within
certain ligaments associated with the vertebral
column; within the walls of the bronchial tubes.
Elastic connective tissue in the wall of the
Connective tissues. (f)
Connective tissue proper. (For a related image,
A Brief Atlas of the Human Body
, Plate 16.)