Ruchi Mathur, MD, FRCP(C) is an Attending Physician with the Division of Endocrinology, Diabetes and Metabolism and Associate Director of Clinical Research, Recruitment and Phenotyping with the Center for Androgen Related Disorders, Department of Obstetrics and Gynecology at Cedars-Sinai Medical Center.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
When I was asked to write an article on "thyroid disease", I took a very deep
breath. The task seemed daunting. As any Endocrinologist (hormone specialist)
knows, there are many subtopics within this giant topic, and an article like
this could go on for a hundred pages! So, once I caught my breath, I decided to
simply design this article to present a "rough guide" to the thyroid. This
article will be an outline or introduction to many conditions that involve the
thyroid gland. As you read through this, you will find a number of links that
will take you to more in-depth articles dealing with the specific topic in
question.
Thyroid 101: What is the thyroid and what does it do?
The thyroid is a butterfly-shaped gland located in the
front of the neck just
below the Adams apple. The gland wraps around the windpipe (trachea) and has a
shape that is similar to a butterfly formed by two wings (lobes) and attached by
a middle part (isthmus). The thyroid gland works like a tiny factory that uses
iodine (mostly from the diet in foods such as seafood and salt) to produce
thyroid hormones. These hormones help to regulate the body's metabolism and
effects processes, such as growth and other important functions of the body.
The
two most important thyroid hormones are thyroxine (T4) and triiodothyronine
(T3), representing 99.9% and 0.1% of thyroid hormones respectively. The hormone
with the most biological power is actually T3. Once released from the thyroid
gland into the blood, a large amount of T4 is converted to T3 - the active
hormone that affects the metabolism of cells throughout our body.
Thyroid hormone regulation - the chain of command
The thyroid itself is regulated by another gland located
in the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid (via a
"feedback" effect of thyroid hormone on the pituitary gland) and by another
gland called the hypothalamus.
The hypothalamus releases a hormone called thyrotropin
releasing hormone
(TRH), which sends a signal to the pituitary to release thyroid stimulating
hormone (TSH). In turn, TSH
sends a signal to the thyroid to release thyroid hormones. If overactivity of
any of these three glands occurs, an excessive amount of thyroid hormones can be
produced, thereby resulting in hyperthyroidism. Similarly, if underactivity of
any of these glands occurs, a deficiency of thyroid hormones can result, causing
hypothyroidism.
Hypothalamus - TRH
Pituitary- TSH
Thyroid - T4 and T3
The rate of thyroid hormone production is controlled by
the pituitary gland. If there is an insufficient amount of thyroid hormone
circulating in the body to allow for normal functioning, the release of TSH is
increased by the pituitary in an attempt to stimulate more thyroid hormone
production. In contrast, when
there is an excessive amount of circulating thyroid hormone, TSH levels fall as
the pituitary attempts to decrease the production of thyroid hormone.
There is another hormone that is produced by the thyroid called calcitonin.
Calcitonin is produced by specific cells in the thyroid gland, and unlike T3 and
T4, it is not involved in this regulation of metabolism. Calcitonin is a hormone
that contributes to the regulation of
calcium and helps to lower calcium levels
in the blood. Excess calcium in the blood is referred to as
hypercalcemia.
The
signs and symptoms of hypothyroidism vary widely and some of the complaints experienced by
individuals with
hypothyroidism include:
fatigue,
mental fogginess and forgetfulness,
feeling excessively cold,
constipation,
dry skin,
fluid retention,
non specific aches and stiffness in muscles and joints,
excessive or prolonged menstrual bleeding (menorrhagia), and
depression.
Hyperthyroidism is suggested by a number of signs and symptoms. People with
mild hyperthyroidism or those older than 70 years of age usually experience no symptoms. In general, the symptoms
become more obvious as the condition worsens. Common symptoms of hyperthyroidism
include:
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Hyperthyroidism is an excess of thyroid hormone resulting from an overactive thyroid gland. Symptoms can include increased heart rate, weight
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