Video Transcript
Which of the following conditions
is characterized by a decrease in thyroid hormones in infants, leading to problems
with growth and often resulting in short stature and impaired development of
secondary sexual characteristics? (A) Myxedema. (B) Exophthalmic goiter, Grave’s
disease. (C) Congenital hypothyroidism,
cretinism. Or (D) hyperglycemia.
This question is asking about the
thyroid gland and the condition caused by a reduced production of its hormones. Let’s review the key facts about
the thyroid gland and the hormones it produces so we can narrow down the options and
answer the question correctly.
The thyroid gland is a
butterfly-shaped endocrine gland found in the neck just in front of the trachea. It uses iodine from your diet to
produce two main hormones, thyroxine and triiodothyronine. Thyroxine is called T4, since its
structure includes four iodine atoms. Tri- means three, so
triiodothyronine has three iodine atoms in its structure and is sometimes called
T3. These hormones are involved in the
control of many functions of the body, including metabolism, heart rate, growth, and
development. The release of thyroxine and
triiodothyronine is controlled by a negative feedback mechanism.
When thyroid hormone levels are low
in the blood, it is detected by the hypothalamus in the brain. This will then release a hormone
called thyrotropin-releasing hormone, or TRH for short, which travels to the
pituitary gland at the base of the brain. The pituitary gland then releases
another hormone called thyroid-stimulating hormone, or TSH. The thyroid-stimulating hormone
then travels in the blood to the thyroid gland, where it binds to receptors on the
cells, stimulating the release of more thyroid hormones, bringing the level back up
to normal.
If thyroid hormone levels are high
in the blood, it is again detected by the hypothalamus. This then releases less
thyrotropin-releasing hormone. So the pituitary gland releases
less thyroid-stimulating hormone and the thyroid gland slows secretion of its
hormones to bring the levels back down.
There are many diseases and
disorders associated with the thyroid gland. These have a variety of causes,
such as malnutrition, cancer, injury, growth of lumps in the thyroid gland, and
problems with the secretory cells.
This question is asking about a
condition that develops in infants, so let’s discuss these options and determine
which is the correct answer. First, we can eliminate option
(D). Hyperglycemia is not associated
with the thyroid at all. It is a condition in which a
person’s blood sugar is too high, hyper- meaning high and glycemia referring to
glucose in the blood. It is most often associated with
diabetes.
Exophthalmic goiter, also known as
Grave’s disease, is an autoimmune disease which causes the thyroid gland to
overproduce its hormones. It often results in an enlarged
thyroid gland, thickening of skin on the shins, and bulging eyes. Because option (B) is referring to
a condition involving high thyroid hormone production and the question refers to
underproduction, we can also eliminate this option.
Myxedema refers to a severe form of
hypothyroidism in adults. Hypo- means low, so this involves
the underproduction of thyroid hormones. Myxedema also refers to the effects
hypothyroidism has on the skin, making it appear swollen. This condition results in many
symptoms, including decreased heart rate, high blood pressure, seizures, and, if
left untreated, coma. Because this condition only occurs
in adults, option (A) can also be ruled out.
This leaves us with congenital
hypothyroidism, also known as cretinism. The word “congenital” describes a
condition existing at or before birth. And as we have discussed,
hypothyroidism is a condition in which the thyroid does not produce sufficient
levels of hormones.
Congenital hypothyroidism is
usually brought about by a lack of iodine in a mother’s diet early on in
pregnancy. This leads to severe hypothyroidism
in the mother and results in irreversible damage to the fetal brain. Obviously, a lack of iodine in the
mother’s diet means the developing child is also short of iodine and therefore
cannot produce enough of the thyroid hormones. This then leads to problems with
growth, often resulting in short stature and impaired development of secondary
sexual characteristics.
Therefore, the correct answer to
this question is (C). The condition characterized by a
decrease in thyroid hormones in infants, leading to problems with growth and often
resulting in short stature and impaired development of secondary sexual
characteristics, is congenital hypothyroidism, cretinism.
