Endocrine system and syndromes

Last Review Date: July 1, 2018

What is the endocrine system?

The endocrine system is made up of various glands located throughout the body. Together with the nervous system, it controls and regulates all bodily functions. While the nervous system uses nerve impulses as a means of control, the endocrine system uses chemical messenger molecules called hormones. These hormones are released by the endocrine glands into the blood stream, where they seek out specific target tissues. The targets have receptors that accept the hormones like fitting a key to a lock. Some of the hormones’ targets are other glands – they are secreted by one gland and travel to another, where they stimulate the production and secretion of another hormone that then takes action. An example of this is the hypothalamus gland (see table on Tests page) that releases thyrotropin-releasing hormone (TRH). This hormone stimulates the pituitary gland to release thyrotropin (more commonly known as TSH or thyroid-stimulating hormone). TSH in turn stimulates the thyroid gland to produce thyroid hormones thyroxine (T4) and triiodothyronine (T3), which help to regulate the rate of metabolism.

To learn more about specific endocrine glands, the hormones they produce, and the disorders associated with their improper function, see the table of endocrine glands on the Tests page.

All of the endocrine glands are normally carefully controlled with the use of feedback systems. For example, the amount of thyroid hormone in the bloodstream acts as a regulating factor on the hypothalamus and pituitary, telling them to release more TRH and TSH respectively when thyroid hormone concentrations in the blood decrease. In some cases, such as thyroid hormone, the body strives to keep a relatively constant amount in the blood.

Some hormones have a daily or monthly pattern of release. For example, cortisol (produced by the adrenal glands) concentrations are high in the morning and lower late in the evening, while both follicle-stimulating hormone (FSH) and luteinising hormone (LH) (produced by the pituitary gland) increase and decrease with and regulate a woman’s monthly menstrual cycle. Other hormones are generally present in very small quantities in the blood and are released in specific situations, such as the release of adrenaline (epinephrine) from the adrenal glands in response to stress.

What can go wrong?

Hormones affect systems all over the body. They control the development of male and female sexual characteristics, fertility, growth, the rate at which the body uses energy, its ability to digest food, to utilise glucose, to respond to stress, to maintain fluid/water balance and to maintain a proper blood pressure. Endocrine abnormalities usually result in the production of either too much of a specific hormone or too little. Some of the conditions that cause dysfunction have been given names, such as Cushing’s syndrome (associated with excess cortisol) because when they occur they cause a typical set of symptoms and complications.

Endocrine gland dysfunction may be due to either a problem with the gland itself, a problem “upstream” in the feedback system, and/or due to a lack of response by the target tissues. There may be decreased hormone production related to trauma, disease, infection, crowding of the hormone-producing cells by a tumour, or due to an inherited gene mutation that affects the quantity, quality, or use of a hormone. Decreased production may also be due to failure of the “upstream” gland to produce its hormone(s). Increased production may also be related to a problem upstream (such as the pituitary producing too much ACTH, leading to the production of too much cortisol), hyperplasia or tumour of the hormone-producing cells, lack of tissue response, medication use or an inherited condition.

Tumours are generally small and usually benign. Most of them are located inside the affected gland and produce a single type of hormone. Rarely they may be cancerous and also rarely they may be located elsewhere in the body. A tumour may cause symptoms because of the excess hormone it is producing, because its growth crowds out and decreases the production of other hormones in the gland, or because its physical size presses against surrounding nerves and structures.

Most inherited conditions are rare and are usually related to deficient or dysfunctional production of a single hormone or to the hormone production of a particular gland (for example, congenital hypothyroidism). However, there are genetically-caused conditions that affect the glands themselves. Two that have been identified as affecting several endocrine glands are MEN-1 and MEN-2 (multiple endocrine neoplasia, types 1 and 2). These conditions are related to alterations in specific genes, and they increase the lifetime risk that those affected will develop tumours in one or more of their endocrine glands.


Table of Endocrine Glands

This table includes a listing of endocrine glands, the hormones they produce, and the diseases and conditions associated with their improper function.
Hypothalamus Lower middle of the brain Growth hormone-releasing hormone (GHRH
Thyrotropin-releasing hormone (TRH)
Corticotropin-releasing hormone (CRH)
Gonadotropin-releasing hormone (GnRH)
Prolactin Inhibitory Factor (PIF, dopamine)
Communicates with both nervous and endocrine systems; 
Stimulates GH, TSH, ACTH, LH/FSH or inhibits prolactin hormone production in the pituitary
Precocious puberty (early GnRH production);
Kallman syndrome (inadequate GnRH production);
Thyroid diseases
Oxytocin Uterine contraction during labour  
Arginine vasopressin (AVP), also called antidiuretic hormone (ADH)- produced by the hypothalamus; stored and secreted by the pituitary Water balance Diabetes insipidus (inadequate AVP production)
Pituitary Below hypothalamus, behind sinus cavity Prolactin Milk production Hypopituitarism
Galactorrhoea (milk production not during pregnancy due to high prolactin)
Growth hormone (GH) Stimulates childhood growth, cell production, helps maintain muscle and bone mass in adults

Acromegaly or Gigantism (excess GH)
Growth Hormone
Deficiency (GHD)


Stimulates cortisol Cushing's syndrome (excess ACTH)
TSH Stimulates thyroid hormone Hyperthyroidism
LHFSH Regulation of testosterone and oestrogen, fertility Loss of menstrual period
Loss of sex drive
Thyroid Butterfly-shaped; lies flat against windpipe in the throat T4 (thyroxine)
T3 (triiodothyronine)
Helps regulate the rate of metabolism Thyroid diseases (including hypo & hyperthyroidism)
Calcitonin Helps regulate bone status, blood calcium  
Parathyroid 4 tiny glands located behind, next to, or below the thyroid Parathyroid hormone (PTH) Regulates blood calcium Hyperparathyroidism
Adrenal 2 triangular organs, on top of each kidney Adrenaline
Blood pressure regulation, stress reaction Phaeochromocytoma 
Aldosterone Salt & water balance Conn’s syndrome
Cortisol Stress reaction Cushing’s syndrome
Addison’s disease
DHEA-S Body hair development at puberty Cancer
Adrenal hyperplasia
(females only)
2 located in the pelvis Oestrogen
Female sexual characteristics Polycystic ovary syndrome (PCOS)
(males only)
2 located in the groin Testosterone Male sexual characteristics Hypogonadism
Pancreas Large, gourd-shaped gland, located behind the stomach Insulin
Glucose regulation Diabetes mellitus
Zollinger-Ellison syndrome
Pineal Lower side of the brain Melatonin Not well understood;
Helps control sleep patterns, affects reproduction


The goal with endocrine gland testing is to identify the hormone(s) that are being over- or under-produced, to determine which gland(s) are involved, and to determine the cause. This may involve measuring hormone levels and their metabolites in the blood and/or urine. It may also involve stimulation or suppression testing to evaluate hormone production and/or its “upstream” hormone stimulation (to find out if it is the gland itself that is dysfunctional or if it is due to dysfunction by the gland preceding it). If a tumour is suspected, then imaging scans may be used to help locate the tumour. If symptoms are suspected to be due to an inherited condition, then genetic testing may be recommended. Patients often see an endocrinologist (an endocrine gland specialist) to help them determine the appropriate testing and treatment. Related testing on this site includes:

Laboratory tests

Non-laboratory tests

  • Magnetic resonance imaging (MRI)
  • Computed tomography (CT)
  • Ultrasound
  • Radioisotope scans


Treatment of endocrine gland-related conditions depends on the cause. If the problem is due to a drug therapy, then the patient may be able to be weaned off the medication (never abruptly stop taking a medication without consulting with your doctor). If it is due to hyperplasia, then the action of the hormone may be able to be blocked. If is due to a tumour, then the tumour may be able to be surgically removed. Often this will resolve the problem or decrease it to the point that it can be successfully controlled.

In some cases, after a gland has been removed to resolve the problem, the patient may need to take replacement medications, such as thyroid hormone. Replacement is also often used when a patient’s gland has been damaged or is otherwise not capable of producing a sufficient quantity of one or more hormones. When patients have a gene mutation associated with MEN-1 or MEN-2, careful lifetime monitoring will be necessary. Treatment of all endocrine-related conditions should be tailored to the individual. Patients should work with their doctor to determine the right course of action for them.

Related pages

On this site
Tests: ACTH, aldosterone, cortisol, calcitonin, calcium, catecholamines, plasma and urine, DHEAS, electrolytes, FSH, GH, hCG, IGF-1, LH, metanephrines, plasma free and urine, oestrogen, progesterone, prolactin, PTH, free T3, free T4, testosterone, TSH
Conditions: Adrenal insufficiency & Addison’s disease, Cushing’s syndrome, Conn’s syndrome

Elsewhere on the web
MedlinePlus Medical Encyclopedia: Endocrine Glands
Nemours Foundation: Endocrine System, KidsHealth for Parents
Healthdirect Australia: Endocrine diseases