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.
About the author:
Kristy Haugen is a mother working to finish her second bachelor
degree in Chemical Engineering. She is also a Licensed Practical
Nurse with a current bachelor degree in Biology and Chemistry.
She writes to inform consumers about nutrition and health
topics. Learn more about your health and buy liquid vitamins
online at
http://www.vitaminmaniac.com/provitamintext.htm
