by Kristy Haugen
Copyright 2006 Kristy Haugen
The thyroid is a gland located on the anterior
(front) portion of the neck attached to the upper part of the trachea
(windpipe). The thyroid is a bi-lobed gland. This gland is small in
size, about 4 centimeters long and 1-2 centimeters wide.
The thyroid produces and secretes biologically
important hormones. Tissue in the thyroid is made up of two different
kinds of cells: follicular and parafollicular cells. The thyroid is
composed mostly of follicular cells which secrete T3 and T4 hormones.
The T4 hormone (thyroxine) and T3 hormone (triiodothyronine) is derived
from the amino acid tyrosine during iodination of the amino acid.
Parafollicular cells secrete the hormone calcitonin. Iodine is important
in the function of the thyroid gland. Iodine is a chief component of the
hormones produced by the thyroid gland. Iodine deficiency can cause
thyroid dysfunction, hence the need for iodized salt. The thyroid also
produces and secretes the hormone calcitonin. The hormone calcitonin
decreases plasma calcium ions concentration by inhibiting the release of
calcium ions from the bone. Calcitonin secretion is regulated by plasma
calcium ion levels.
The thyroid plays a key role in regulating the
body’s metabolism. What is metabolism? Metabolism is a chemical
reaction that occurs in the body’s cells, releasing energy from the
nutrients ingested. Metabolism also uses energy to create other
biologically important substances such as proteins. Basal metabolic rate
(BMR) is a measurement of the body’s required energy to keep
functioning at rest (measured in calories). Exertion, stress, fear, and
illness increase the body’s metabolic rate.
The thyroid has many other bodily functions. The
thyroid helps regulate calcium levels in the body. The thyroid can
increase the body’s temperature, thus burning more calories. This in
turn increases the body’s appetite. The thyroid also promotes glucose
catabolism. Catabolism is the break down of complex glucose forms into
simpler, more usable forms for energy usage. This gland stimulates
protein synthesis, increases lipolysis. Lipolysis is the hydrolysis of
lipids (fats), in which the lipids are broken down into simpler or
usable forms. The thyroid also promotes normal heart function, normal
neural development in fetus and growing infants, and normal neural
function in adults.
The thyroid is influenced by hormones produced by
the pituitary gland and the hypothalamus. The pituitary gland is located
at the base of the brain. This gland produces thyroid stimulating
hormone (TSH). TSH stimulates the thyroid gland to absorb iodine and
then synthesize and release thyroid hormones.
The hypothalamus is located above the pituitary
gland in the brain. This hormone produces thyrotropin releasing hormone
(TRH). The hypothalamus and pituitary gland detect low levels of thyroid
hormones in the blood. TRH is released by the hypothalamus to stimulate
the pituitary gland to release TSH. TSH in turn stimulates the thyroid
gland to produce more T3 and T4 hormones. This returns the thyroid
hormone levels in the blood back to normal.
Inflammation of the thyroid or a deficiency in
iodine causes the condition called hypothyroidism. The thyroid hormones
become under secreted or are not secreted at all with hypothyroidism.
Hypothyroidism symptoms include fatigue, slowed heart and respiratory
rate, cold intolerance, and weight gain. Newborn infants with
hypothyroidism (cretinism) are characterized by mental retardation and
short stature.
The thyroid can also be over stimulated in a
condition termed hyperthyroidism. This results in over secretion of the
thyroid hormones. Symptoms associated with this disorder include an
increased metabolic rate, profuse sweating, heart palpitations, weight
loss, protruding eyes, and a feeling of excessive warmth. With both
conditions the thyroid often enlarges resulting in goiter. However,
goiter does not always indicate disease. Thyroid enlargement can result
during pregnancy and puberty.
If you exhibit some of the above symptoms, you
should consult your physician for further follow up. Many women due have
serious concerns regarding their thyroid gland. If you have tried to
lose weight with no success, maybe it is due to the thyroid
