CHAPTER 4
Connective Tissue
57
Figure 4-15A,B
Dense Regular Connective Tissue, Tendon
Figure 4-15C
Clinical Correlation: Tendinosis
Figure 4-16A,B
Loose Connective Tissue
Synopsis 4-2
Functions of Connective Tissue
Figure 4-17A,B
Loose Connective Tissue, Small Intestine
Figure 4-17C
Clinical Correlation: Whipple Disease
Types of Connective Tissue: Specialized Connective Tissues
Figure 4-18A,B
Adipose Tissue
Figure 4-18C
Clinical Correlation: Obesity
Figure 4-19A,B
Reticular Connective Tissue
Figure 4-19C
Clinical Correlation: Cirrhosis
Figure 4-20A,B
Elastic Connective Tissue
Figure 4-20C
Clinical Correlation: Marfan Syndrome—Cystic Medial Degeneration
Types of Connective Tissue: Embryonic Connective Tissues
Figure 4-21A
Mesenchyme, Embryo
Figure 4-21B
Mucous Connective Tissue
Synopsis 4-3
Pathological Terms for Connective Tissue
Table 4-3
Connective Tissue Types
Introduction and Key Concepts
for Connective Tissue
Connective tissue
provides structural support for the body by
binding cells and tissues together to form organs. It also provides
metabolic support by creating a hydrophilic environment that
mediates the exchange of substances between the blood and tissue.
Connective tissue is of mesodermal origin and consists of a mixture
of
cells
,
± bers
,
and
ground substance
. The hydrophilic
ground sub-
stance
occupies the spaces around cells and ± bers.
Fibers
(
collagen
,
elastic
, and
reticular
) and the ground substances constitute the
extracellular matrix of connective tissue. The classi± cation and
function of connective tissue are based on the differences in the
composition and amounts of cells, ± bers, and ground substance.
Connective Tissue Cells
A variety of cells are found in connective tissue, which differ
according to their origin and function. Some cells
differentiate
from mesenchymal cells, such as adipocytes and ± broblasts;
these cells are formed and reside in the connective tissue and are
called
± xed cells
. Other cells, which arise from hematopoietic
stem cells, differentiate in the bone marrow and migrate from
the blood circulation into connective tissue where they perform
their functions; these mast cells, macrophages, plasma cells,
and leukocytes are called
wandering cells
(Fig. 4-1). Cells found
in connective tissue proper include
± broblasts
,
macrophages
,
mast cells
,
plasma cells
,
and
leukocytes
(Figs. 4-2 to 4-4). Some
cells, such as
f broblasts
, are responsible for synthesis and
maintenance of the extracellular material. Other cells, such as
macrophages
,
plasma
cells
, and
leukocytes
, have defense and
immune functions.
FIBROBLASTS
are the most common cells in
connective
tissue. Their nuclei are ovoid or spindle shaped and can be
large or small in size depending on their stage of
cellular
activity. They have pale-staining cytoplasm and contain
well- developed rough endoplasmic reticulum (RER) and rich
Golgi complexes. With routine H&E staining, only the very
thin,
elongated nuclei of the cells are clearly visible. Their
thin, pale-staining cytoplasm is usually not obvious. They are
responsible for the synthesis of all components of the extracel-
lular matrix (±
bers and ground substance) of connective tissue
(Figs. 4-2, 4-3, and 4-7).
MACROPHAGES,
also called
tissue
histiocytes
, are highly
phagocytic cells that are derived from blood monocytes. With
conventional staining, macrophages are very dif± cult to iden-
tify unless they show visible ingested material inside their
cytoplasm. Macrophages may be named differently in certain
organs (Figs. 4-2 and 4-3). For example, they are called
Kupffer
cells
in the liver,
osteoclasts
in bone, and
microglial cells
in the
central nervous system.
MAST CELLS
are of bone marrow origin and are distributed
chiefl
y around small blood vessels. They are oval to round in
shape, with a centrally placed nucleus. With toluidine blue stain,
large basophilic purple staining granules are visible in their
cytoplasm. These granules contain and release
heparin
,
hista-
mines
, and various chemotactic mediators, which are involved
in infl
ammatory responses. Mast cells contain Fc membrane
receptors, which bind to immunoglobulin (Ig) E antibodies, an
important cellular interaction involved in anaphylactic shock
(Fig. 4-4A,B).
PLASMA CELLS
are derived from B lymphocytes. They are
oval shaped and have the ability to secrete antibodies that are
antigen speci±
c. Their histological features include an eccentri-
cally placed nucleus, a cartwheel pattern of chromatin in the
nucleus, and basophilic-staining cytoplasm due to the
presence
of abundant RER and a small, clear area near the nucleus. This
cytoplasmic clear area (
Golgi zone
[
GZ
]) marks the position of
the Golgi apparatus (Figs. 4-2 and 4-3).
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