Thyroid cancer

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The thyroid

The thyroid is a gland in the front of the neck below the larynx (voice box) and near the trachea (windpipe). It is part of the endocrine system. The thyroid makes hormones that control many body functions.

Diagram of the location and structure of the thyroid

Structure of the thyroid

The thyroid is shaped like a butterfly and has a right and left lobe. The lobes are joined by a thin piece of tissue called the isthmus. Inside the thyroid are many small, round sacs called follicles. The follicles make, store and release thyroid hormones.

The thyroid is made up of and contains different types of cells. The follicles are lined with follicular cells. C cells (also called parafollicular cells) are scattered throughout the thyroid, including in the lining of and between the follicles. Other types of cells within the thyroid include lymphocytes (a type of white blood cell) and fat cells (called adipocytes).

Thyroid hormones

The thyroid makes hormones that control the body’s growth, development and metabolism (how the body uses energy). These hormones help:

  • break down food and change it into energy
  • control body temperature
  • control heart rate and blood pressure
  • control breathing
  • keep the nervous system working normally
  • the brain develop in children

Thyroxine (T4) and triiodothyronine (T3)

The follicular cells take in iodine from the blood, which is used to make the hormones T4 and T3. Iodine is a mineral we get from certain foods. In developed countries like Canada, iodine is added to table salt to make sure it is part of the diet and the body can make enough thyroid hormones to keep it working properly.

The follicular cells also make thyroglobulin (Tg). Tg is a protein that stores T4 and T3 until the body needs them.

How much T4 and T3 the thyroid makes is controlled by thyroid-stimulating hormone (TSH, or thyrotropin). TSH is a hormone made by the pituitary gland.


C cells in the thyroid make the hormone calcitonin. Calcitonin helps control the level of calcium in the blood. It does this by slowing down the release of calcium from bones and increasing the amount of calcium excreted from the kidneys into the urine.


A specialized organ or group of cells that produces or releases substances (such as hormones, saliva, digestive juices, sweat, tears or milk) to perform different functions in the body.

endocrine system

The group of glands and cells in the body that make and release hormones (which control many functions such as growth, reproduction, sleep, hunger and metabolism) into the blood.

The endocrine system is made up of the hypothalamus, pituitary gland, pineal gland, thyroid, parathyroid gland, adrenal gland, pancreatic islet cells (also known as islets of Langerhans) and the ovaries or testicles.

nervous system

The network of neurons (nerve cells) throughout the body that work together to control organ functions and body movements.

The nervous system is made up of the central nervous system (CNS) and peripheral nervous system (PNS).

pituitary gland

The main endocrine system gland at the base of the brain that produces hormones to control other glands and many body functions, including growth.

Also called the hypophysis.