132
UNIT 1
Organization of the Body
4
is found in the skin as the leathery
dermis
, and it forms fibrous
joint capsules and the fibrous coverings that surround some or-
gans (kidneys, bones, cartilages, muscles, and nerves).
Elastic Connective Tissue
A few ligaments, such as those con-
necting adjacent vertebrae, are very elastic. Te dense regular
connective tissue in those structures is called
elastic con-
nective tissue
(Figure 4.8f). Additionally, many of the larger
arteries have stretchy sheets of elastic connective tissue in
their walls.
Cartilage
Cartilage
(kar
9
tĭ-lij), which stands up to both tension
and
com-
pression, has qualities intermediate between dense connective
tissue and bone. It is tough but flexible, providing a resilient
rigidity to the structures it supports.
Cartilage lacks nerve fibers and is avascular. It receives its nu-
trients by diffusion from blood vessels located in the connective
tissue membrane (perichondrium) surrounding it. Its ground
substance contains large amounts of the GAGs chondroitin sul-
fate and hyaluronic acid, firmly bound collagen fibers (and in
some cases elastic fibers), and is quite firm. Cartilage matrix also
contains an exceptional amount of tissue fluid. In fact, cartilage
is up to 80% water! Te movement of tissue fluid in its matrix
enables cartilage to rebound a±er being compressed and also
helps to nourish the cartilage cells.
with great resistance to tension (pulling forces) where the ten-
sion is exerted in a single direction. Crowded between the colla-
gen fibers are rows of fibroblasts that continuously manufacture
the fibers and scant ground substance.
Collagen fibers are slightly wavy (see Figure 4.8d). Tis al-
lows the tissue to stretch a little, but once the fibers straighten
out, there is no further “give” to this tissue. Unlike our model
(areolar) connective tissue, this tissue has few cells other than
fibroblasts and is poorly vascularized.
With its enormous tensile strength, dense regular connec-
tive tissue forms
tendons
, which are cords that attach muscles
to bones; flat, sheetlike tendons called
aponeuroses
(ap
0
o-nu-
ro
9
sēz) that attach muscles to other muscles or to bones; and the
ligaments
that bind bones together at joints. Ligaments contain
more elastic fibers than tendons and are slightly more stretchy.
Dense regular connective tissue also forms fascia (fash
9
e-ah; “a
bond”), a fibrous membrane that wraps around muscles, groups
of muscles, blood vessels, and nerves, binding them together
like plastic sandwich wrap.
Dense Irregular Connective Tissue
Dense irregular connec-
tive tissue
has the same structural elements as the regular va-
riety. However, the bundles of collagen fibers are much thicker
and they are arranged irregularly; that is, they run in more than
one plane (Figure 4.8e). Tis type of tissue forms sheets in body
areas where tension is exerted from many different directions. It
Figure 4.8
(continued)
Connective tissues. (c)
Connective tissue proper. (For a related
image, see
A Brief Atlas of the Human Body
, Plate 13.)
(c)
Connective tissue proper: loose connective tissue, reticular
Description:
Network of reticular fibers in a
typical loose ground substance; reticular cells
lie on the network.
Function:
Fibers form a soft internal skeleton
(stroma) that supports other cell types
including white blood cells, mast cells, and
macrophages.
Location:
Lymphoid organs (lymph nodes,
bone marrow, and spleen).
Photomicrograph:
Dark-staining network of reticular connective
tissue fibers forming the internal skeleton of the spleen (350
m
).
Spleen
White blood cell
(lymphocyte)
Reticular
fibers
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