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The endocrine system and hormones

The endocrine system is a group of glands and cells in the body that make hormones and release them into the blood. Hormones are natural substances that act like chemical messengers between different parts of the body. They control many functions including growth, reproduction, sexual function, sleep, hunger, mood and metabolism. Certain cells in the body have proteins called receptors that react to a hormone. How the cell responds depends on which hormone it is reacting to.

There are many organs and glands that make up the endocrine system.

Pituitary gland

The pituitary gland is the main gland of the endocrine system. It is at the base of the brain and makes and stores many hormones that control:

  • growth
  • metabolism
  • the making of breast milk after giving birth
  • menstruation, maturing eggs and the making of estrogen by the ovaries in women
  • the making of sperm and testosterone by the testicles in men
  • steroid levels in the body

The hormones made by the pituitary gland also cause other endocrine glands to make or stop making other hormones. Together, the pituitary gland and hypothalamus control the endocrine system and hormone levels in the body.

Find out more about the pituitary gland.

Hypothalamus

The hypothalamus is an important part of the brain and has many jobs controlling different parts of the body. One of the jobs of the hypothalamus is to make hormones, including those that control the pituitary gland and control blood pressure. The hypothalamus reacts to changes in hormone levels in the body.

Pineal gland

The pineal gland is a tiny gland deep in the brain that makes the hormone melatonin, which controls sleep patterns.

Thyroid

The thyroid is a butterfly-shaped gland in the neck in front of the upper part of the windpipe (trachea). The thyroid makes hormones that control many body functions including growth and metabolism. It also makes a hormone that controls the amount of calcium in the body.

Find out more about the thyroid.

Parathyroid gland

The parathyroid glands are 4 small glands attached to the back of the thyroid. They make and release parathyroid hormone. Parathyroid hormone helps control calcium levels in the blood. Most calcium is stored in the bones. When calcium levels in the blood are low, the parathyroid glands make PTH to get the bones to release calcium into the blood. When calcium levels in the blood are high, the parathyroid glands make less PTH, and calcium levels in the blood lower.

Thymus

The thymus is a gland in the upper part of the chest, just behind the breastbone (sternum) and between the lungs. The thymus is part of the endocrine system, the lymphatic system and the immune system. The thymus makes hormones that help T cells (a type of white blood cell) to mature and function.

Find out more about the thymus.

Adrenal glands

We have 2 adrenal glands, one on top of each kidney. The adrenal glands make several hormones that control different body functions, including metabolism, heart rate, blood pressure and water and salt balance. They also make small amounts of the sex hormones estrogen and testosterone.

Find out more about the adrenal glands and adrenal gland hormones.

Pancreas

The pancreas is a slim, long organ in the upper left part of the abdomen that sits under the stomach between the liver and spleen. The pancreas is part of the digestive and endocrine systems. The pancreas makes enzymes that are released directly into the small intestine to help digest food. It also makes hormones that help with digestion and control blood sugar (glucose) levels (such as insulin). The hormones are made in small groups of specialized cells in the pancreas called islets. This part of the pancreas that makes hormones is called the endocrine pancreas.

Find out more about the pancreas.

Ovaries

The ovaries are part of a woman’s reproductive system (female reproductive system). Women have 2 ovaries where immature eggs develop into mature eggs (ova). The ovaries also make the hormones estrogen and progesterone. The ovaries are deep inside a woman’s pelvis, on both sides of the uterus (womb) close to the ends of the fallopian tubes.

Find out more about the ovaries.

Testicles

The testicles (testes) are a part of a man’s reproductive system (male reproductive system). A man has 2 testicles. The testicles make sperm and the male sex hormone testosterone.

Find out more about the testicles.

Neuroendocrine system and neuroendocrine cells

The neuroendocrine system is made up of special cells called neuroendocrine cells. They are scattered throughout the body. Neuroendocrine cells act like nerve cells (neurons) and also make hormones like cells of the endocrine system (endocrine cells). Neuroendocrine cells receive messages (signals) from the nervous system and respond by making and releasing hormones.

Neuroendocrine cells are scattered along the gastrointestinal (GI) tract and are found in the gallbladder, lungs, hypothalamus, pituitary gland, thyroid, parathyroid glands, pancreas and inner layer of the adrenal gland (adrenal medulla).

Find out more about the neuroendocrine system.

Heart and kidneys

The heart and kidneys also play a role in the endocrine system. They make hormones that help control blood pressure and the amount of blood inside the body (called blood volume). The kidneys also make a hormone that makes the body absorb calcium from the food we eat.

Hormones and cancer

Some hormones can cause cancer to grow and some cancers make hormones that lead to problems in the body.

Hormone receptors

Estrogen and progesterone are female sex hormones. They can cause breast cancer cells to grow. Some types of breast cancer cells have estrogen receptors (ER) and progesterone receptors (PR) on their surface or inside the cell. When hormones attach to these receptors, they can cause the cancer cells to grow and divide.

Women who are diagnosed with breast cancer will have hormone receptor status testing to see if they may benefit from treatment with hormonal therapy.

Hormonal therapy

Some types of cancers use hormones to grow, such as breast and prostate cancers. So doctors sometimes use hormonal therapy to treat cancer. Hormonal therapy is a treatment that adds, blocks or removes hormones to stop or slow the growth of cancer cells that need hormones to grow. Find out more about hormonal therapy.

Paraneoplastic syndrome

Some people with cancer develop a condition called paraneoplastic syndrome. A paraneoplastic syndrome is a group of symptoms that develop when cancer cells release chemicals that can change how other organs and tissues work. For example, some types of lung cancer make hormones that prevent the kidneys from working properly so they can’t remove extra calcium from the blood. This causes a condition of high blood calcium levels called hypercalcemia.

Artificial hormones

Sometimes you can get artificial hormones from outside sources, such as drugs or chemicals in the environment. Hormones from outside sources can raise or lower your hormone levels in the body. Sometimes, changes in hormone levels can raise or lower the risk of cancer. Artificial hormones include:

  • birth control pills and other hormonal contraceptives
  • hormonal replacement therapy
  • anabolic steroids
  • endocrine disruptors (for example, bisphenol A found in some plastics)
  • Find out more about artificial hormones and how they may increase the risk of cancer.

Cancers of the endocrine system

Cancer can develop anywhere in the body, and some types of cancer start in the organs and cells of the endocrine system. These cancers may increase hormone levels, which can cause problems in the body. Cancers of the endocrine system include:

  • neuroendocrine tumours (NETs)
  • some brain and pituitary gland tumours
  • thyroid cancer
  • parathyroid cancer
  • thymus cancer
  • adrenal gland cancer
  • pancreatic islet cell cancer
  • some ovarian cancers
  • some testicular cancers

gland

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.

metabolism

The chemical processes in the body that create and use energy. It includes breaking down food and transforming it into energy, eliminating wastes and toxins, breathing, circulating blood and regulating temperature.

Metabolic means referring to or having to do with metabolism, as in metabolic rate.

enzyme

A protein that speeds up certain chemical reactions in the body.

For example, enzymes in the intestines help to digest food.

gastrointestinal (GI)

Referring to or having to do with the digestive organs.

The gastrointestinal (GI) tract, or digestive tract, includes the mouth, pharynx (throat), esophagus, stomach, small intestine and large intestine.

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