What is the thyroid?

The thyroid is a small butterfly-shaped gland measuring 2 inches, located just under the skin, in front of the neck. Many vital body functions are controlled by the thyroid gland. The thyroid gland produces and releases (secretes) certain hormones (mainly thyroid) that control the speed of metabolism (metabolic rate). Metabolism is the process of transforming the food that is consumed into energy which is then utilized for the normal body processes.

What is the function of thyroid gland?

Many essential functions depend on the thyroid hormones – the heart rate, the rate at which calories are burned, healthy skin maintenance, normal growth, heat production. Functions such as fertility and digestion are also affected by the normal thyroid gland functioning.

Hence, any problem in the thyroid impacts the entire body and its functioning.

What are the hormones associated with thyroid?

There are 2 major hormones that are produced and secreted by the thyroid.

T4: Thyroxine

Although T4 is the major thyroid hormone being produced and released in the body, it has a very small effect in speeding up the body’s metabolic rate. T4 is mainly converted to T3, the more active hormone. The conversion of T4 to T3 occurs in the liver and other tissues and this conversion happens depending on factors such as the body’s energy needs or the presence or absence of illnesses.

T3: Triiodothyronine

Although produced in lesser amounts, the effect of T3 is substantially greater than T4.

The other hormones produced by the thyroid gland is the hormone calcitonin, which aids in development of bone strength by incorporating calcium into bone.

Iodine is required to produce thyroid hormones. The thyroid gland traps iodine and transforms it into thyroid hormones. An imbalance of Iodine may affect the affect the thyroid hormone levels, thereby affecting certain body functions. This may lead to thyroid diseases.

How does the body adjust thyroid hormones?

The level of thyroid hormones is adjusted by a complex mechanism. A gland located in the brain (pituitary), produces the thyroid-stimulating hormone (TSH). The TSH further stimulates the thyroid gland to produce thyroid hormones. If the level of thyroid hormone is low in the blood, then the pituitary gland increases the release of TSH which then stimulates the production of thyroid hormone, and if the level of thyroid is high, the pituitary reduces TSH release.

What are the conditions and disorders affecting the thyroid?

In India, every third person suffers from some form of thyroid disorder. The resulting weight gain and hormonal imbalances occur mostly in women. Thyroid diseases are divided into primary and secondary – primary when the disease initiates from the thyroid gland and secondary when the disease initiates in pituitary gland. (Example: Excess thyroid hormone release due to a nodule present on the thyroid is called primary hyperthyroidism. An excess secretion of TSH because of pituitary gland tumour would indirectly cause an increased thyroid hormone production. This is known as secondary hyperthyroidism.

Four main conditions that affect the thyroid:

  • Hypothyroidism (underactive thyroid).
  • Hyperthyroidism (overactive thyroid).
  • Goiter (enlarged thyroid).
  • Thyroid cancer (cancer of the thyroid tissue).

What are the early warning signs and symptoms of thyroid problems?

There may be different symptoms for every thyroid condition. However, because thyroid affects multiple body systems and processes, there are certain symptoms to indicate a thyroid disease:

  • Slow or rapid heart rate.
  • Unexplained weight loss or weight gain.
  • Difficulty tolerating cold or heat.
  • Depression or anxiety.
  • Irregular menstrual periods.

Consult the doctor in case any of these symptoms are observed. The doctor might check for normal thyroid functioning.

Diagnostic tests of the thyroid gland:

Measuring the levels of thyroid-stimulating hormone (TSH) is the first-line test for checking normal thyroid function. The levels of T4 and T3 are also measured.

The normal range for TSH is between 0.4 and 4.0 milliunits per liter (mU/L), according to the American Thyroid Association, with the upper limit generally being between 4 to 5. This level may vary among different labs. Pregnancy and age also affect the range.

Doctor may also suggest a thyroid scan or a thyroid ultrasound depending on the result of the blood test.

  • In a thyroid scan, a small amount of a radioactive substance (such as iodine or technetium) is injected into the bloodstream and when this material concentrates in the thyroid gland, it produces a picture of the thyroid gland depicting physical abnormalities, if any.
    • An ultrasound may be recommended by the doctor if one or more growths (nodules) in the thyroid gland is felt. Ultrasonography uses sound waves to measure the size of the gland, determine if a growth is solid or filled with fluid (cystic), and check the details of the nodule (presence or absence of calcium)


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