The thyroid gland
consists of two connected lobes and is the largest endocrine gland in
vertebrates. It is in common parlance said to have a butterfly shape. The
thyroid gland is found below the “Adam’s apple” (the laryngeal prominence) in
humans. It controls our sensitivity to other hormones, how the body makes
proteins and uses energy. The thyroid
produces two main hormones thyroxine (T4) and triiodothyronine (T3).
Triiodothyronine is also referred to as tetraiodothyronine, triiodo referring
to 3 iodine molecules. T3 and T4 form triggers for the functioning of most
other systems of the body. The main components of T3 and T4 are thyrosine and
iodine. The thyroid assists calcium homeostasis by producing cacitonin. Calcium
homeostasis helps maintain sufficient levels of calcium in the body.
Thyroid-stimulating
hormone (TSH), produced by the pituitary gland triggers the thyroid to produce
T3 and T4. The pituitary gland is in turn regulated by thyrotropin-releasing
hormone (TRH) which is produced in the hypothalamus.
The thyroid gland is made-up
of two lobes or wings, the left lobe referred to as lobus sinister and the right lobe called lobus
dexter. Both lobes are 3 cm wide, 5 cm long and 2 cm thick. The thyroid is
located on the frontal side of the neck below the Adams apple. Occasionally
there is a third lobe, the pyramidal lobe present forming part of the thyroid.
This lobe is a remnant of the fetal thyroglossal duct. The thyroid gland weighs
18-60 grams in adults and even more in women during pregnancy.
There are two types of
dysfunctions of the thyroid gland, Hypothyroidism and Hyperthyroidism. In
Hypothyroidism the gland produces less than sufficient levels of thyroid hormones and in
Hyperthyroidism the hormones are produced in excess.
Hypothyroidism
Hypothyroidism is a common thyroid disorder.
The symptoms of hypothyroidism are fatigue, intolerance to cold, weight gain,
inability to concentrate, dryness of the skin, hair loss and more. It may lead
to delayed growth and intellectual impairment in children. It is called cretinism
in extreme cases. The diagnosis of hypothyroidism is a simple blood test measuring
thyroid-stimulating hormone, thyroxine and triiodothyronine. The lab range for
TSH is between 0.30 to 5.5 measured in uIU/ml (international units per
milliliter), the lab range for T3 is 60 – 200 ng/dl (nanogram/deciliter) and
the lab range for T4 is 4.5 to 12 ug/dl (microgram/deciliter). However labs may
use different measurement representations. There is however a debate in the
medical community about the reference range of TSH used by testing labs for screening hypothyroid
patients. It is being advocated that the upper limit be reduced from 5.5 to 3.0 uIU/ml.
The most common cause of hypothyroidism is
deficiency of iodine in the diet. So the best preventive measure is to include iodized
salt and other foods containing iodine. Hashimoto’s thyroiditis is an autoimmune disorder;
it is another common cause of this thyroid syndrome. Some other causes of
hypothyroidism are a thyroid surgery, malfunctioning or injured pituitary
gland and the hypothalamus. There are many instances of the thyroid not
functioning since birth. Hypothyroidism can be easily treated with artificially manufactured hormone
supplementation. The dose is usually adjusted according to TSH and thyroxine
normalization levels, taking into account clinical symptoms.
Deferred relaxation
after the ankle jerk reflex test is a distinctive sign of hypothyroidism, other
signs and symptoms are: fatigue, dry coarse skin, feeling cold, cool
extremities, poor memory and concentration, Myxedema, constipation, dyspepsia,
hair loss, weight gain with poor appetite, slow pulse rate, shortness of
breath, swelling of the limbs, hoarse voice, delayed relaxation of tendon
reflexes, heavy menstrual periods, carpal tunnel syndrome, abnormal sensations,
pleural effusion, ascites, pericardial effusion, poor hearing.
Hyperthyroidism
Hyperthyroidism is a
condition in which the thyroid gland makes excessive amounts of thyroid
hormones. The condition is also referred to as hyperthyreosis
or overactive thyroid.
In hyperthyroidism both thyroid hormones (T3 and T4) circulating in the body are over produced. The most
common cause of hyperthyroidism is Graves’ disease. Thyrotoxicosis is caused by
hyperthyroidism. Thyrotoxicosis is a clinical syndrome which occurs due to
extreme elevation of T3 and T4 in blood serum. However, Thyrotoxicosis may
occur without hyperthyroidism and may be attributed to swelling of the thyroid
gland. Thyrotoxicosis may be exogenous in nature and could happen due to
accidental excessive ingestion of the prescription thyroid hormone.
Hyperthyroidism is a
condition more difficult to manage than hypothyroidism. The management of
hyperthyroidism involves the use of antithyroid drugs, suppressing the thyroid
function. However, a more permanent solution is radioisotope therapy or
surgery. All methods have the risk of inducing hypothyroidism. Hyperthyroidism
has a high probability of being cancerous in origin.
Every function of the
body speeds up, if there is too much thyroid hormone. Hence, some symptoms of
hyperthyroidism are nervousness, vomiting, irritability, lightened menstrual
flow, increased perspiration, frequent bowel movement, racing heart, hand
tremors, weight loss, anxiety, difficulty sleeping, thinning of the skin, fine
brittle hair, and muscular weakness.