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Quick Facts

Overview of the Thyroid Gland


The Manual's Editorial Staff

Last full review/revision Jul 2020| Content last modified Jul 2020
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What is the thyroid gland?

Your thyroid is a gland below the Adam’s apple in the front of your neck. Glands make and release hormones. Hormones stimulate other cells or tissues into action. The thyroid makes thyroid hormones.

Locating the Thyroid Gland

Locating the Thyroid Gland

What are thyroid hormones?

Thyroid hormones control how fast your body’s chemical functions work (your metabolic rate). Almost every cell in your body needs thyroid hormones. Among many other things, thyroid hormones help control:

  • How fast you burn calories

  • How fast your heart beats

  • Your body temperature

There are 2 thyroid hormones:

  • T3

  • T4

Iodine is needed by your thyroid gland in order to make thyroid hormones. You need only a tiny amount of iodine. But if your thyroid gland doesn't get iodine, it won't make enough thyroid hormones (a condition called hypothyroidism).

What controls thyroid hormones?

The pituitary gland in your brain makes a hormone called TSH.

  • TSH tells your thyroid gland to make thyroid hormones

If your pituitary gland detects too little thyroid hormone in your blood, it puts out more TSH to stimulate your thyroid gland to make more thyroid hormones. If there's too much thyroid hormone in your blood, your pituitary puts out less TSH. Then your thyroid gland makes less thyroid hormone.

How do doctors test your thyroid gland?

The main tests of your thyroid gland are:

  • Blood tests

  • Imaging tests

Blood tests for the thyroid measure the level of:

  • Thyroid hormones

  • TSH

A high TSH level usually means you don't have enough thyroid hormones. And a very low TSH level usually means you have too much.

Imaging tests include:

  • Ultrasound, to tell whether your thyroid is enlarged

  • Nuclear scans

In a nuclear scan, doctors give you a tiny amount of radioactive iodine. Because your thyroid gland needs iodine, it collects the radioactive iodine. Doctors detect the radioactive iodine with a special camera. If your thyroid gland isn't working, it won't take up the iodine normally. The camera can also detect any small growths (nodules) on your thyroid. The scan doesn't use enough radiation to harm you.

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