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What the hormone system is

The hormone system is a network of glands and organs in the body that produce hormones. It is also called the endocrine system. The main parts of the hormone system are shown in the diagram below.

Diagram showing the hormone system


Hormones and how they work

Hormones are natural substances made by the glands and organs of the hormone system. Our bloodstream carries the hormones around the body. Each gland makes a different hormone and most make more than one.

There are many different hormones.  They act as chemical messengers between one part of the body and another. Each one works on the particular cells that are able to receive and respond to that hormone’s message. 

Each hormone has a different purpose. Generally speaking, they control how we respond to changes in the environment around us, as well as

  • Growth and development
  • How the body works
  • Our mood
  • Sexual function
  • Reproduction

After a hormone is released, it travels from the gland to its target cells through the bloodstream. It connects to a part of the target cell called a receptor. The connection triggers a response in the cell. The type of response depends on the type of hormone.

The hypothalamus and the pituitary gland in the brain control the whole hormone system and levels of hormones in the body.


The hypothalamus and hormone level control

The hypothalamus is part of the brain and not actually part of the endocrine system.

Diagram showing the parts of the brain

The hypothalamus works with the pituitary gland to control the activity of most of the other glands of the endocrine system. It reacts to changes in the amount of hormones in the body. When the level of a particular hormone drops below what it should be, the hypothalamus signals to the pituitary gland. The pituitary then produces hormones that tell other organs to produce the hormone that the body needs.

For example, the thyroid gland makes thyroid hormones. It only does this when the hypothalamus detects that the level of thyroid hormones is low. The hypothalamus signals to the pituitary gland to produce thyroid stimulating hormone (TSH). TSH stimulates the thyroid to produce thyroid hormones. When the thyroid hormones are at the right level, the hypothalamus signals to the pituitary gland to stop producing TSH. The thyroid gland then stops making thyroid hormones. This system is called a negative feedback mechanism and is how the body controls hormone levels.


The pituitary gland

This is a small gland at the base of the brain. It makes a number of hormones and controls many different body functions. Many of the pituitary gland hormones signal to other parts of the hormone system to make, or stop making, other hormones.

Diagram showing the position of the pituitary gland in the brain

Pituitary hormones control

  • Growth, by producing growth hormone
  • The speed of body processes (metabolism) - thyroid stimulating hormone (TSH) tells the thyroid gland to make thyroid hormones
  • Steroid levels - adrenocorticotropic hormone (ACTH) tells the adrenal glands to make steroids
  • Breast milk production after birth - prolactin makes the breasts produce milk
  • Periods and egg production in women
  • Sperm and testosterone production in men

Egg and sperm production are controlled by two pituitary hormones, follicle stimulating hormone (FSH) and luteinising hormone (LH). These control oestrogen and progesterone levels in women and testosterone levels in men. FSH and LH levels are in turn controlled by the hypothalamus.


The pineal gland

The pineal gland is a very small gland deep in the brain. It makes the hormone melatonin, which controls sleep patterns. 

Diagram showing the position of the pineal gland in the brain


The thyroid and parathyroid glands

The thyroid gland is at the base of the neck. 

Diagram showing the position of the thyroid and parathyroid glands

The thyroid makes these hormones

  • T3 - also called tri iodothyronine
  • T4 - also called thyroxine
  • Calcitonin

The hormones T3 and T4 help to control how fast your body works – your metabolic rate. If your thyroid gland doesn’t make enough of these hormones, you put on weight and feel very tired and lacking in energy.

If your thyroid gland makes too much of the T3 and T4 hormones, you lose weight and have an increased appetite. With an overactive thyroid you may also feel anxious and find it difficult to relax.

Calcitonin helps to control the amount of calcium in the body.

There are 4 parathyroid glands. They are very small glands at the base of your neck very close to the thyroid gland. They make parathyroid hormone (PTH). Along with calcitonin and vitamin D, PTH controls the level of calcium in the body.


The adrenal glands

You have two adrenal glands - one above each kidney. They make several hormones. Cortisol is a natural steroid hormone that affects the level of sugar in the blood. Aldosterone helps to regulate the body’s water and salt balance, and the blood pressure.

The adrenal glands also produce small amounts of the male and female sex hormones (oestrogen and testosterone).

Probably the best known hormone made in the adrenal gland is adrenalin (epinephrine), which helps us to respond quickly when under stress. Another similar hormone, noradrenalin (norepinephrine), also helps us to respond quickly under stressful conditions.


The pancreas

The pancreas is quite high up in your abdomen. It lies across the body, where your ribs meet at the bottom of your breastbone, just behind your stomach. You can see the position of the pancreas in the diagram above. It is about 6 inches long and shaped like a leaf. The pancreas makes insulin, which controls the amount of sugar in our blood. It also makes other hormones that help with digestion, including glucagon, somatostatin and pancreatic polypeptide.


The ovaries

The ovaries produce 2 sex hormones, oestrogen and progesterone. Together they control the menstrual cycle (periods).

During puberty oestrogen helps the development of female sexual characteristics, including breast growth and the maturing of the womb (uterus) and vagina.

Progesterone plays a part in maintaining pregnancy.


The testes

The testicles or testes produce the hormone testosterone. Testosterone gives male qualities such as a deep voice and beard growth. It also controls sex drive (libido) and the ability to have an erection.

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Updated: 24 July 2013