The thyroid gland

The thyroid is a small gland in the front of your neck just below your voice box (larynx). It is made up of two parts called lobes.

What is the thyroid gland?

The thyroid is a small gland in the front of your neck, just below your voicebox (larynx). It is made up of 2 parts called lobes. The lobes are connected by a thin piece of thyroid tissue called the isthmus.


This illustration shows the position of the thyroid gland. It is in the lower middle part of the neck, shaped a bit like a butterfly. The thyroid gland is made up of two lobes, the left lobe and the right lobe. Behind and above the thyroid gland is the windpipe, made up of the larynx and the trachea. Either side of the thyroid gland, and under the chin are some lymph nodes. The nodes are joined together by fine tubes called lymph vessels.
Image: The thyroid gland



What does your thyroid gland do?

The thyroid gland is part of the endocrine system. This system makes hormones that help control the way your body functions. Your thyroid gland makes the following hormones:

  • thyroxine (T4)
  • triiodothyronine(T3)
  • calcitonin.

Thyroid hormones T3 and T4

These hormones keep your body functioning at the right speed.

If your thyroid gland does not make enough hormones, your body’s cells work slower than normal. You usually feel tired and put on weight more easily. This is called hypothyroidism, or an underactive thyroid.

If your thyroid gland makes too many hormones, your body’s cells work faster than normal. This is called hyperthyroidism, or an overactive thyroid. You usually lose weight, feel hungrier than normal, and feel shaky and anxious. Your heartbeat may be faster than normal or irregular.

A part of your brain called the hypothalamus senses if the levels of T3 and T4 in your blood are too low. If they are, it sends thyroid-releasing hormones (TRH) into your blood. The rising level of TRH makes another gland in the brain (pituitary gland) release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce more T3 and T4. If your brain senses that the levels of T3 and T4 are too high, it sends messages to lower the amount of TSH.

This his diagram shows how the brain controls T3 and T4 levels in your blood. It shows a circle made up of 4 arrows pointing in a clockwise direction. Normal levels are at the top of the circle. Going round in a clockwise direction, it shows how decreased levels of T3 and T4 make your hypothalamus release thyroid-releasing hormones (TRH). These make your pituitary gland release thyroid-stimulating hormone (TSH), which then makes the thyroid gland release T3 and T4. The levels of T3 and T4 in the blood are increased and this completes the circle back to normal levels.
Image: Thyroid hormones

Most people with thyroid cancer have normal levels of T3 and T4.

The thyroid gland needs a regular supply of iodine to produce thyroid hormones. We get iodine from our diet. It is mainly found in fish, seafood and dairy products. Some types of salt also contain iodine, but they are not commonly used in the UK.


Calcitonin helps to control the amount of calcium in the blood. It works together with another hormone called parathyroid hormone (PTH), which is made in the parathyroid glands. These are 4 very small glands behind the thyroid gland. Calcium helps:

  • your muscles and nerves work
  • to build strong bones
  • your blood to clot.

The lymphatic system

The lymphatic system helps to protect us from infection and disease. It is made up of fine tubes called lymphatic vessels. These vessels connect to groups of small lymph nodes throughout the body. The lymphatic system drains lymph fluid from the tissues of the body before returning it to the blood.

The diagram shows the network of lymph nodes throughout the body. There are nodes in the neck (cervical), armpit (axilla) and groin (inguinal). The diagram shows the thymus gland at the top of the chest area, and the spleen, which is on the left side of the abdomen. The diagram also shows the diaphragm, which is the muscle that separates the chest from the abdomen.
Image: The lymphatic system

Lymph nodes are sometimes called lymph glands. They filter bacteria (germs) and disease from the lymph fluid. When you have an infection, some lymph nodes may swell as they fight the infection.

Thyroid cancer cells can sometimes spread to the lymph nodes in the neck and chest.

About our information

  • References

    Below is a sample of the sources used in our thyroid cancer information. If you would like more information about the sources we use, please contact us at

    British Medical Journal. Best Practice Guidelines, Thyroid cancer. 2020.

    European Society Medical Oncology (ESMO): Thyroid cancer, Clinical Practice Guidelines for Diagnosis, Treatment and Follow-up. 2019.

    National Institute for Health and Care Excellence (NICE). TA535: Lenvatinib and Sorafenib for treating differentiated thyroid cancer after radioactive iodine. 2018. [accessed May 2021].

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Professor Nick Reed, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 June 2021
Next review: 01 June 2024
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.