CHAPTER 4
Connective Tissue
77
Types of Connective Tissue: Embryonic Connective Tissues
Figure 4-21A.
Mesenchyme, embryo.
H&E,
3
136; inset
3
408 (
left
) and
3
438 (
right
)
Mesenchyme
(
mesenchymal connective tissue
) is found in
the developing structures in the
embryo
. It contains scat-
tered
reticular ±
bers
and
mesenchymal cells
, which have
irregular, star or spindle shapes and pale-stained cytoplasm.
These cells exhibit
cytoplasmic processes
, which often give
the cells a stellate appearance. Mesenchymal cells are rela-
tively unspecialized and are capable of
differentiating
into
different cell types in mature tissue cells, such as cartilages,
bones, and muscles.
Embryonic red blood cells
can be seen
in this specimen. These blood cells contain a nucleus in each
cell; this is characteristic of their immature state (anucle-
ated red blood cells are characteristic of the mature state
and are found in adult tissues). Interestingly enough, some
vertebrates, such as frogs and chickens, have nucleated red
blood cells in the adult state.
Figure 4-21B.
Mucous connective tissue, umbilical cord.
Toluidine blue stain,
3
68; inset
3
178
An example of
mucous connective tissue
that has an abun-
dance of a
jellylike matrix
with some F
ne aggregates of col-
lagen F
bers and stellate-shaped
± broblasts
is shown. It is
found in the umbilical cord and subdermal connective tis-
sue of the embryo. Mucous tissue is a major constituent of
the umbilical cord, where it is referred to as
Wharton jelly
.
This type of connective tissue does not differentiate beyond
this stage. In this example, the viscous ground
substance has
been stained with a special stain to reveal
jellylike mucin
,
which contains
hyaluronic acid
and
glycoproteins
.
Colla-
gen ±
bers
and large stellate-shaped
± broblasts
(not mesen-
chymal cells) predominate in the mucous tissue.
Mesenchymal
cells
Embryonic red blood
cells
Mesenchymal
connective
tissue
Cytoplasmic
processes
Mesenchymal
cells
A
Mucous
Mucous
connective
tissue
connective tissue
Smooth muscle
Smooth muscle
Mucous
connective
tissue
Smooth muscle
Fibroblasts
Fibroblasts
Fibroblasts
B
SYNOPSIS 4-3
Pathological Terms for Connective Tissue
Urticaria
: An itchy skin eruption, also known as
hives
, characterized by wheals with pale interiors and well-deF
ned red
margins, often the result of an allergic response to insect bites, foods, or drugs (±ig. 4-3C).
Pruritis
: Itching of the skin due to a variety of causes including hyperbilirubinemia and allergic and irritant contact condi-
tions (±ig. 4-3C).
Cirrhosis
: An abnormal liver condition characterized by diffuse nodularity, due to F
brosis and regenerative nodules of
hepatocytes; frequent causes are alcohol abuse and viral hepatitis (±ig. 4-19C).
Jaundice
: Yellow staining of the skin, mucous membranes, or conjunctiva of the eyes caused by elevated blood levels of
the bile pigment bilirubin (±ig. 4-19C).
Coagulopathy
: A disorder that prevents the normal clotting process of blood; causes may be acquired, such as hepatic dys-
function, or congenital, such as decreased clotting factors, as seen in inherited conditions like hemophilia (±ig. 4-19C).
Necrosis
: Irreversible cell changes that occur as a result of cell death (±ig. 4-20C).
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