CHAPTER 3
Epithelium and Glands
33
Simple Cuboidal Epithelium
A
Simple
cuboidal
epithelium
Colloid
Simple
cuboidal
epithelium
D. Cui
Cuboidal cell
Basement membrane
Connective tissue
B
Figure 3-5A.
Simple cuboidal epithelium, thyroid
gland.
H&E,
3
155; inset
3
537
Simple cuboidal epithelial cells that line the thyroid
follicles of the thyroid gland are called
follicular cells
.
Adjacent follicles are separated by a thin layer of con-
nective tissue, containing occasional F
broblasts. ±olli-
cular cells are normally
cuboidal
in shape but become
columnar when stimulated or in a state of hyperfunc-
tion (
hyperthyroidism
—excessively high levels of
thyroid hormone secretion). At the other extreme,
these cells may become fl
attened and squamous—like
when they are inactive or in a state of hypofunction
(
hypothyroidism
—excessively low levels of thyroid
hormone secretion).
±ollicular cells synthesize and release a precursor
(thyroglobulin)
of thyroid hormones
(T3 and T4)
into
the lumen of the follicle where it forms the colloid.
Thyroid hormones are essential for normal brain and
body development in infants and for the regulation of
the metabolic rate in adults, and they affect the func-
tion of every organ system.
Figure 3-5B.
A representation of simple cuboidal epithelium
lining the thyroid follicle.
A layer of
cuboidal cells
rests on a thin
basement membrane
. The
nuclei are round and located in the center of the cell. These cells
have a large amount of
rough endoplasmic reticulum (RER)
and
an elaborate
Golgi complex
in the cytoplasm, which refl ects their
high metabolic activity and production of secretory granules con-
taining thyroglobulin. The thyroglobulin is secreted via
exocytosis
into the follicular lumen, where it is stored as a
colloid
. The api-
cal (luminal) surface of these cuboidal cells is characterized by
numerous short microvilli.
CLINICAL CORRELATION
Figure 3-5C.
Hyperthyroidism.
Hyperthyroidism
is a condition characterized by the
overproduction of thyroid hormone. In this condition,
the follicular cells have changed from cuboidal cells to
become
columnar cells
as a result of their high activity.
Symptoms include nervousness, irritability, increased heart
rate
(tachycardia)
, increased perspiration, difF
culty sleep-
ing, muscle weakness, warm moist skin, trembling hands,
and hair loss. This disorder is seen most often in women
20 to 40 years age.
Graves disease
, the most common form
of hyperthyroidism, results from antibodies in the blood
that mimic thyroid-stimulating hormone, stimulating the
thyroid to grow and secrete excessive thyroid hormone.
Symptoms of thyroid hyperfunction also can be induced
by excessive thyroid hormone medication.
At the other extreme, in
hypothyroidism
, there are
very low levels of thyroid hormone secretion and follicular
cells become fl
at, squamous cells; the patient may experi-
ence weight gain, somnolence, fatigue, and depression.
D. Cui
D. Cui
Hypothyroidism
Connective
tissue
Basal membrane
Active columnar cell
C
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