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 voice box (larynx). It is made up of two parts called lobes. The lobes are connected by a thin bridge of thyroid tissue called the isthmus.

This image 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 wind pipe, 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.

What does your thyroid gland do?

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

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

Thyroid hormones T3 and T4

These keep your body functioning at the right speed.

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

If your thyroid gland makes too many hormones, your body’s cells will work faster than normal. This is called hyperthyroidism, thyrotoxicosis or an overactive thyroid. You may 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, called the pituitary gland, release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce more T3 and T4.

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.

Most people who have a thyroid gland 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.


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 four very small glands behind the thyroid gland. Calcium helps your muscles and nerves work, builds strong bones and helps your blood to clot.

The lymphatic system

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

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.

Lymph nodes (sometimes called lymph glands) are small and bean-shaped. They filter bacteria (germs) and disease from the lymph fluid. When you have an infection, lymph nodes often swell as they fight it.

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