The Thyroid Gland: Functions, Calcitonin & TSH

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  • 0:05 Thyroid Gland
  • 1:52 T3 and Thyroxine (T4)
  • 4:03 TSH
  • 5:13 Calcitonin
  • 6:34 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Your thyroid gland produces the hormones T3 and thyroxine (T4), which play a role in metabolism. Your thyroid also produces calcitonin, which helps regulate blood calcium levels. In this lesson, you will learn about the thyroid gland and its hormones, including how they are regulated by TSH.

Thyroid Gland

The thyroid gland is wrapped around the windpipe.
Thyroid Gland Location

At the base of your neck, just below your Adam's apple, lies a hormone-producing gland called the thyroid gland. In this lesson, you will learn about the anatomical features of this gland and the functions of the three hormones it produces: T3, T4, and calcitonin.

But, before we get started, let's talk about the thyroid gland itself. I bet you have heard of the thyroid gland before. This gland is familiar to most people because it often gets the blame for a slow metabolism and weight gain. It is true that the thyroid gland plays an important role in your metabolic rate. It's also true that an underactive thyroid gland can leave a person feeling tired and sluggish - and cause that person to experience weight gain. However, these symptoms can also result from an unhealthy lifestyle, and in many cases, the thyroid gland gets more blame than it deserves. So, let's take a closer look at the thyroid gland and how it helps your body function properly.

Your thyroid gland is an endocrine gland that secretes hormones that control metabolism and body growth. As mentioned earlier, it is found at the base of your neck and wraps itself around your trachea, or windpipe. When you look at a drawing of the thyroid gland, it almost resembles a butterfly with its wings wide open sitting on a plant stem. The 'wings' are actually the two lobes of the thyroid gland. If you were to take a look inside these lobes, you would notice many hollow structures called thyroid follicles. These follicles contain a protein-rich fluid, from which we get the thyroid hormones T3 and T4.

T3 and Thyroxine (T4)

These thyroid hormones are somewhat unique because they need iodine in order to be produced. Therefore, you need to take in iodine for your thyroid gland to function properly. You get iodine from foods such as dairy products and seafood, and even if you avoid these foods, you likely get enough iodine in your diet due to the fact that salt is often iodized - meaning that it has iodine added. It is interesting to note that because the thyroid gland absorbs nearly all of the iodine in your body, iodine can be made into a radioactive isotope and given to a patient as radioactive iodine to assess the health of the thyroid.

Triiodothyronine, or T3, contains three atoms of iodine.

In your body, iodine is combined with an amino acid, and from this combination we get the two thyroid hormones that are important to your metabolism. If the hormone has three iodine atoms attached to it, we call it T3, or triiodothyronine. This term is not easy to pronounce, but it is easy to recall if you break it down. For instance, we know that the prefix 'tri-' means 'three,' and the term 'iodo' refers to 'iodine.' So, this hormone is composed of three iodine atoms. T3 is a powerful thyroid hormone that affects almost every process in the body, including metabolism, body temperature, growth and development, and heart rate.

In the same way we just learned about T3, if the hormone as four iodine atoms attached to it, we call it T4, or tetraiodothyronine. We see that the prefix 'tetra-' means 'four.' However, T4 is not often referred to as tetraiodothyronine. It is far more common to refer to this hormone as T4 or thyroxine. You can recall that thyroxine is a thyroid hormone by noticing that both words start with the letters 't-h-y-r-o.' Thyroxine is very similar to T3, and we see that T3 and T4 work together to control processes in the body, including metabolism, body temperature, growth and development, and heart rate.


As we are learning from studying the endocrine system, the hormonal output of one endocrine gland is often dependent on the hormones from another endocrine gland. This is the case when we look at the thyroid. Thyroid-stimulating hormone (TSH) is a hormone that stimulates the thyroid gland to produce T3 and T4. We previously learned that thyroid-stimulating hormone is secreted by the anterior pituitary gland, which is the important master gland that is responsible for affecting many body organs.

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