CHAPTER 4
Connective Tissue
59
This tissue also forms conduits through which blood vessels
and nerves course.
SPECIALIZED CONNECTIVE TISSUES
Adipose Tissue
is a special form of connective tissue, con-
sisting predominantly of
adipocytes
that are the primary site for
fat storage and are specialized for heat production. It has a rich
neurovascular supply.
Adipose tissue
can be divided into
white
adipose
tissue
and
brown
adipose
tissue
.
White
adipose
tissue
is composed of unilocular adipose cells. The typical appearance
of cells in white adipose tissue is lipid stored in the form of
a single, large droplet in the cytoplasm of the cell. The fl at-
tened nucleus of each adipocyte is displaced to the periphery
of the cell. White adipose tissue is found throughout the adult
human body (Fig. 4-18).
Brown
adipose
tissue
, in contrast, is
composed of
multilocular adipose cells
. The lipid is stored in
multiple droplets in the cytoplasm. Cells have a central nucleus
and a relatively large amount of cytoplasm. Brown adipose tis-
sue is more abundant in hibernating animals and is also found
in the human embryo, in infants, and in the perirenal region in
adults.
Reticular Tissue
is a specialized loose connective tissue that
contains a network of branched reticular ±
bers,
reticulocytes
(specialized ± broblasts), macrophages, and parenchymal cells,
such as pancreatic cells and hepatocytes. Reticular ±
bers are
very ±
ne and much smaller than collagen type 1 and elastic
±
bers. This tissue provides the architectural framework for
parenchymal organs, such as lymphoid nodes, spleen, liver,
bone marrow, and endocrine glands (Fig. 4-19).
Elastic Tissue
is composed of bundles of thick elastic ±
bers
with a sparse network of collagen ± bers and ± broblasts ±
ll-
ing the interstitial space. In certain locations, such as in elastic
arteries, elastic material and collagen ± bers can be produced by
smooth muscle cells. This tissue provides fl exible support for
other tissues and is able to recoil after stretching, which helps to
dampen the extremes of pressure associated with some organs,
such as elastic arteries (Fig. 4-20). Elastic tissue is usually found
in the vertebral ligaments, lungs, large arteries, and the dermis
of the skin.
EMBRYONIC CONNECTIVE TISSUES
is a type of loose tis-
sue formed in early embryonic development.
Mesenchymal con-
nective
tissue
and
mucous
connective
tissue
also fall under this
category.
Mesenchymal Connective Tissue
is found in the embryo and
fetus and contains considerable ground substance. It contains
scattered reticular ± bers and star-shaped mesenchymal cells that
have pale-staining cytoplasm with small processes (Fig. 4-21A).
Mesenchymal connective tissue is capable of differentiating into
different types of connective tissues (Fig. 4-1A).
Mucous Connective Tissue
exhibits a jellylike matrix with
some collagen ±
bers and stellate-shaped ± broblasts. Mucous
tissue is the main constituent of the umbilical cord and is called
Wharton jelly
(see Fig. 4-21B). This type of tissue does not dif-
ferentiate beyond this stage. It is mainly found in developing
structures, such as the umbilical cord, subdermal connective
tissue of the fetus, and dental pulp of the developing teeth. It is
also found in the nucleus pulposus of the intervertebral disk in
adult tissue.
SUPPORTING CONNECTIVE TISSUE
is related to car-
tilage and bone. Cartilage is composed of chondrocytes and
extracellular matrix; bone contains osteoblasts, osteocytes,
and osteoclasts and bone matrix. These will be discussed in
Chapter 5, “Cartilage and Bone.”
HEMATOPOIETIC
TISSUE
(BLOOD
AND
BONE
MARROW)
is a specialized connective tissue in which cells are
suspended in the intercellular fl
uid, and it will be
discussed in
Chapter 8, “Blood and Hemopoiesis.”
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