Endocrine organs

The endocrine system – 10 amazing glands

The thyroid gland is part of your endocrine Endocrine
“relating to glands which secrete hormones or other products directly into the blood”
system. It may be helpful for people with a thyroid problem to understand which part the thyroid plays in the endocrine system.

Graphic showing the male and female endocrine system

The endocrine system is a collection of glands that produce hormones (chemical messengers). These hormones pass directly into the bloodstream to control metabolism Metabolism
“the chemical processes within the human body”
, growth and sexual development.

The endocrine system consists of the following glands:

  • hypothalamus
  • pituitary gland Pituitary gland
    “the major endocrine gland, a pea-sized body attached to the base of the brain that is important in controlling growth and development and the functioning of the other endocrine glands”
  • pineal gland
  • thyroid gland
  • parathyroid glands Parathyroid glands
    “four small pea-sized glands located in the neck just behind the thyroid gland which control calcium levels in the bloodstream”
  • adrenal glands
  • pancreas Pancreas
    “a large gland behind the stomach, which secretes digestive enzymes into the duodenum”
  • thymus
  • testes (male)
  • ovaries (female)

The hormones produced by these glands travel to various organs, glands and tissues Tissues
“groups of cells that have a similar structure and act together to perform a specific function”
in the body and communicate with them. Once they have reached their particular organ Organ
“part of the body that performs a special task such as heart and kidney”
or tissue they bind to specific proteins Proteins
“plant or animal tissue”
on the surface of the cell. These proteins are called receptors Receptors
“a specialised cell or group of nerve endings that responds to things such as hormones”
. When they have bound to the receptor, this causes a response in that particular organ or tissue (they tell it what to do).

Sometimes things can go wrong in the endocrine system and various illnesses can be caused.

What the endocrine system’s glands do


The hypothalamus is part of the brain. It receives messages from all over the body and keeps the body balanced by sending out messages to the Nervous System via the brain. It also sends out hormone messages to the pituitary Pituitary
“of or relating to the pituitary gland”
gland and helps to regulate the control of thirst and hunger.

Pituitary Gland

The pituitary gland is under the control of the hypothalamus and is connected to the hypothalamus by a stalk. It has two lobes – the anterior Anterior
“situated before or at the front”
lobe Lobe
“a round projection or division such as ear lobe or the lobes of the thyroid gland”
and the posterior Posterior
“situated behind or at the rear”

The anterior lobe of the pituitary gland produces the following hormones:

  • Follicle-stimulating Hormone (FSH) and Luteinizing Hormone (LH) which control the production of the sex hormones ( oestrogen Oestrogen
    “the primary female sex hormone. Also known as estrogen ”
    and testosterone). They also control the growth and release of the egg from the ovaries. In men, they control the production of sperm.
  • Growth Hormone which controls growth.
  • Thyroid Stimulating Hormone Thyroid Stimulating Hormone
    “produced by the pituitary gland its role is to regulate the production of hormones by the thyroid gland”
    (TSH) which tells the thyroid gland to produce and release thyroid hormones.
  • Adrenocorticotropic Hormone Adrenocorticotropic Hormone
    “ACTH is made in the pituitary gland – it is needed for your adrenal glands to work properly and help your body react to stress”
    (ACTH) which tells the adrenals to release the hormone cortisol Cortisol
    “a steroid hormone that regulates a wide range of processes throughout the body, including metabolism and the immune response. It also has a very important role in helping the body respond to stress”
  • Melanocyte-Stimulating Hormone (MSH) which controls the production of melanin. Melanin is the substance that gives skin its colour.
  • Prolactin (PRL) which stimulates the production of breast milk and is necessary for normal milk production during breastfeeding.

The posterior lobe of the pituitary gland produces the following hormones:

  • Antidiuretic hormone (ADH) which controls water excretion by the kidneys.
  • Oxytocin which causes the womb to contract during labour and plays a role in the production of breast milk.

Pineal Gland

The pea-sized pineal gland is near the centre of the brain. The pineal gland produces a hormone called melatonin. Melatonin is the hormone which is responsible for closing the body down ready for sleep. It is produced when it is dark so more is produced at night and in the winter. When nights are longer, the body makes more melatonin.

It also affects reproductive development, thyroid and adrenal cortex functions.

Thyroid Gland

The thyroid gland is a small butterfly-shaped gland with two lobes. It is situated in the front of your neck, just below the Adams Apple.

The thyroid gland produces two main hormones which are very important for growth and development. One is called thyroxine Thyroxine
“the main hormone secreted into the bloodstream by the thyroid gland. It is the inactive form”
(T4) and the other is called triiodothyronine Triiodothyronine
“alternative name is T3. Triiodothyronine is the active form of the thyroid hormone, thyroxine”
(T3). T4 is converted to T3 in the body’s cells and tissues. T3 is an active hormone and is needed by all of the cells and tissues of the body.

The thyroid gland also produces another hormone called calcitonin, which works alongside parathyroid hormone Parathyroid hormone
“parathyroid hormone (PTH) is a hormone secreted by the parathyroid glands that regulates the serum calcium through its effects on bone, kidney, and intestine”
in the maintenance of calcium Calcium
“a mineral found in many foods. The body needs calcium to maintain strong bones and to carry out many important functions. Almost all calcium is stored in bones and teeth, where it supports their structure and hardness”
levels in the blood.

Parathyroid Glands

These pea-sized glands are attached to the thyroid gland and produce parathyroid hormone (PTH) which controls blood calcium levels.

Adrenal Glands

The adrenal glands are situated at the top of the kidneys. Each adrenal gland Adrenal gland
“a small gland located on top of the kidney. The adrenal glands produce hormones that help control heart rate, blood pressure, the way the body uses food, the levels of minerals such as sodium and potassium in the blood, and other functions particularly involved in stress reactions”
is divided into two areas, the cortex and the medulla. Each area produces different hormones.

The cortex produces Corticosteroid hormones:

  • Cortisol (also known as hydrocortisone Hydrocortisone
    “a steroid hormone produced by the adrenal cortex and used medicinally to treat inflammation resulting from eczema and rheumatism”
    ) is the main stress-buster of the body and controls the body’s use of fats, proteins and carbohydrates.
  • Corticosterone helps to control the immune system Immune system
    “the organs and processes in the body that work together to resist infections”
    ’s inflammatory response ( inflammation Inflammation
    “redness, swelling, pain, tenderness, heat, and disturbed function of an area of the body”

It also produces Mineralocorticoids such as Aldosterone Aldosterone
“a corticosteroid hormone which stimulates absorption of sodium by the kidneys and so regulates water and salt balance”
, which helps to maintain sodium balance in the body and the maintenance of blood volume and blood pressure.

The cortex also produces Gonadocorticoids or sex hormones such as testosterone, oestrogen, DHEA DHEA
”or dehydroepiandrosterone – a hormone produced by the body’s adrenal glands”
and progesterone Progesterone
“an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species”
in small amounts.

The medulla produces Adrenaline Adrenaline
“a hormone secreted by the adrenal glands that increases rates of blood circulation, breathing, and carbohydrate metabolism and prepares muscles for exertion”
and Noradrenaline Noradrenaline
“a hormone which is released by the adrenal medulla, increasing blood pressure and heart rate, and by the sympathetic nerves and functions as a neurotransmitter”
in response to acute stress such as fright and anger. These cause the heart to pump harder and the heart rate to increase. They also open airways into the lungs, increase blood flow to major muscle groups and enable the body to fight or run in a stressful situation.


The pancreas produces digestive enzymes and certain special cells which control blood sugar, producing the hormones insulin Insulin
“a hormone produced in the pancreas which regulates the amount of glucose in the blood”
and glucagon Glucagon
“a hormone formed in the pancreas which promotes the breakdown of glycogen to glucose in the liver”


The thymus makes white blood cells called T-lymphocytes. These white blood cells are part of the body’s immune system and help to fight infection.


The testes are two egg-shaped male reproductive organs. They produce the hormone testosterone, which is responsible for the male characteristics of the body. Testosterone is needed for the production of sperm. Men also produce a small amount of progesterone and oestrogen.

The Ovaries

The ovaries are two oval-shaped female reproductive organs. They produce the female sex hormones oestrogen and progesterone, which are responsible for the female characteristics of the body. Oestrogen strengthens bones and has a protective effect on the heart, and progesterone causes the womb’s lining to thicken ready for pregnancy. The ovaries also produce small amounts of testosterone.

Date updated: 20/08/21 (V1.2)
Review date: 24/05/22