The Endocrine System

What Does The Endocrine System Do?

Many of our body’s functions – growth, metabolism, sexual development and function, among others – are controlled by the endocrine system, which consists of glands that make and secrete regulatory chemicals called hormones.

Hormones are secreted into the bloodstream in one part of the body and travel through the bloodstream to control what happens in another part.

Endocrine System

What Makes Up The Endocrine System?

The Endocrine system consists of the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive glands (the ovaries and the testes). The pancreas is also part of this hormone-secreting system, even though it is also associated with the digestive system because it produces and secretes digestive enzymes.

Although the endocrine glands are the body’s main hormone producers, some non-endocrine organs — such as the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta — also produce and release hormones.


Hypothalamus and PituitaryThe hypothalamus is part of the brain that lies just above the pituitary gland. It releases hormones that start and stop the release of pituitary hormones.

The hypothalamus controls hormone production in the pituitary gland through several “releasing” hormones. Some of these are growth hormone-releasing hormone, or GHRH (controls GH release); thyrotropin-releasing hormone, or TRH (controls TSH release); corticoptropin-releasing hormone, or CRH (controls ACTH release).


Even though it is no larger than the size of a pea, the pituitary gland is sometimes called the “master gland” because of its great influence on the other body organs.

Located just below the hypothalmus, the pituitary gland is divided into two parts, front (anterior) and back (posterior).

The anterior pituitary produces several hormones:

  • Prolactin or PRL – PRL stimulates milk production from a woman’s breasts after childbirth and can affect sex hormone levels in the ovaries in women and the testes in men.

  • Growth hormone or GH – GH stimulates growth in childhood and is important for maintaining a healthy body composition. In adults it is also important for maintaining muscle mass and bone mass. It can affect fat distribution in the body.

  • Adrenocorticotropin or ACTH – ACTH stimulates production of cortisol by the adrenal glands. Cortisol, a so-called “stress hormone, helps maintain blood pressure and blood glucose levels, and is vital to survival.

  • Thyroid-stimulating hormone or TSH – TSH stimulates the thyroid gland to make thyroid hormones, which, in turn, control (regulate) the body’s metabolism, energy, growth and development, and nervous system activity.

  • Luteinizing hormone or LH – LH regulates testosterone in men and estrogen in women.

  • Follicle-stimulating hormone or FSH – FSH promotes sperm production in men and stimulates the ovaries to release eggs (ovulate) in women. LH and FSH work together to allow normal function of the ovaries or testes.

The posterior pituitary produces two hormones:

  • Oxytocin – Oxytocin causes milk in nursing mothers and contractions during childbirth.

  • Antidiuretic hormone or ADH – ADH, also called vasopressin, regulates water balance. If this hormone is not secreted properly, this can lead to problems of sodium (salt) and water balance, and could also affect the kidneys so that they do not work as well.

In response to over- or underproduction of pituitary hormones, the target glands affected by these hormones can produce too many or too few hormones of their own. For example, too much growth hormone can cause gigantism, or excessive growth, while too little GH may cause dwarfism, or very short stature.


ThyroidThe thyroid, located in the front part of the lower neck, below the Adam’s apple, is shaped like a bow tie or butterfly and produces the thyroid hormones thyroxine and triiodothyronine. These hormones control the rate at which cells burn fuels from food to produce energy. As the level of thyroid hormones increases in the bloodstream, so does the speed at which chemical reactions occur in the body.

Thyroid hormones also play a key role in bone growth and the development of the brain and nervous system in children. The production and release of thyroid hormones is controlled by thyrotropin, which is secreted by the pituitary gland.


ParathyroidAttached to the thyroid are four tiny glands that function together called the parathyroids. They release parathyroid hormone, which regulates the level of calcium in the blood with the help of calcitonin, which is produced in the thyroid.

In response to too little calcium in the diet, the parathyroid glands make parathyroid hormone, or PTH, that takes calcium from bones so that it will be available in the blood for nerve conduction and muscle contraction.


AdrenalsThe body has two triangular adrenal glands, one on top of each kidney. The adrenal glands have two parts, each of which produces a set of hormones and has a different function.

The outer part, the adrenal cortex, produces hormones called corticosteroids that influence or regulate salt and water balance in the body, the body’s response to stress, metabolism, the immune system, and sexual development and function.

The inner part, the adrenal medulla, produces catecholamines, such as epinephrine. Also called adrenaline, epinephrine increases blood pressure and heart rate when the body experiences stress. (Epinephrine injections are often used to counteract a severe allergic reaction.)

Pineal Gland

Pineal GlandThe pineal body, or pineal gland, is located in the middle of the brain.

It secretes a hormone called melatonin, which may help regulate the wake-sleep cycle of the body.

Scientists are still learning how the pineal gland works.

Reproductive Glands

The reproductive glands are the testes (in males) and the ovaries (in females).

  • Testes

    TestesMales have twin reproductive glands, called testes, that produce the hormone testosterone. Testosterone helps a boy develop and then maintain his sexual traits. During puberty, testosterone helps to bring about the physical changes that turn a boy into an adult male, such as growth of the penis and testes, growth of facial and pubic hair, deepening of the voice, increase in muscle mass and strength, and increase in height.

    Throughout adult life, testosterone helps maintain sex drive, sperm production, male hair patterns, muscle mass, and bone mass.

  • Ovaries

    OvariesThe two most important hormones of a woman’s twin reproductive glands, the ovaries, are estrogen and progesterone. These hormones are responsible for developing and maintaining female sexual traits, as well as maintaining a pregnancy.

    Along with the pituitary gonadotropins (FH and LSH), they also control the menstrual cycle.

    The most common change in the ovarian hormones is caused by the start of menopause, part of the normal aging process. Loss of ovarian function means loss of estrogen, which can lead to hot flashes, thinning vaginal tissue, lack of menstrual periods, mood changes and bone loss, or osteoporosis.


PancreasThe pancreas is an elongated organ located toward the back of the abdomen behind the stomach. The pancreas has digestive and hormonal functions. One part of the pancreas, the exocrine pancreas, secretes digestive enzymes.

The other part of the pancreas, the endocrine pancreas, secretes hormones called insulin and glucagon. Insulin is a hormone that helps glucose move from the blood into the cells where it is used for energy.

The pancreas also secretes glucagon when the blood sugar is low. Glucagon tells the liver to release glucose, which is stored in the liver as glycogen, into the bloodstream. These hormones regulate the level of glucose (sugar) in the blood.

5 Interesting Facts About The Endocrine System

  1. The endocrine system has no ducts. The hormones it produces are released directly into the bloodstream which carries it to another part of the body.

  2. The endocrine system is responsible for producing about 30 distinct hormones. All these hormones have very distinct jobs to do.

  3. The rush of adrenaline one gets when facing adventure or fear is the result of the adrenal glands production of epinephrine hormone, or adrenaline as we otherwise know it.

  4. We must be grateful to the pineal gland for our sweet sleep. It secretes melatonin which regulates our sleep.

  5. The endocrine system is responsible for the production of insulin. The failure to produce insulin will result in diabetes.

How Does The Endocrine System Work?

Once a hormone is secreted, it travels from the endocrine gland through the bloodstream to target cells designed to receive its message. Along the way to the target cells, special proteins bind to some of the hormones. The special proteins act as carriers that control the amount of hormone that is available to interact with and affect the target cells.

Also, the target cells have receptors that latch onto only specific hormones, and each hormone has its own receptor, so that each hormone will communicate only with specific target cells that possess receptors for that hormone. When the hormone reaches its target cell, it locks onto the cell’s specific receptors and these hormone-receptor combinations transmit chemical instructions to the inner workings of the cell.

When hormone levels reach a normal or necessary amount, further secretion is controlled by important body mechanisms to maintain that level of hormone in the blood. This regulation of hormone secretion may involve the hormone itself or another substance in the blood related to the hormone.

For example, if the thyroid gland has secreted adequate amounts of thyroid hormones into the blood, the pituitary gland senses the normal levels of thyroid hormone in the bloodstream and adjusts its release of thyrotropin, the pituitary hormone that stimulates the thyroid gland to produce thyroid hormones.

Another example is parathyroid hormone, which increases the level of calcium in the blood. When the blood calcium level rises, the parathyroid glands sense the change and decrease their secretion of parathyroid hormone.

This turnoff process is called a negative feedback system.

What Can Go Wrong With Your Endocrine System?

These are some possible endocrine disorders:

Adrenal insuffiency

This condition is characterized by decreased function of the adrenal cortex and the consequent underproduction of adrenal corticosteroid hormones. The symptoms of adrenal insufficiency may include weakness, fatigue, abdominal pain, nausea, dehydration, and skin changes. Doctors treat adrenal insufficiency by giving replacement corticosteroid hormones.

Cushing Syndrome

Excessive amounts of glucocorticoid hormones in the body can lead to Cushing Syndrome. In children, it most often results when a child takes large doses of synthetic corticosteroid drugs (such as prednisone) to treat autoimmune diseases such as lupus. If the condition is due to a tumor in the pituitary gland that produces excessive amounts of corticotropin and stimulates the adrenals to overproduce corticosteroids, it’s known as Cushing Disease.

Symptoms may take years to develop and include obesity, growth failure, muscle weakness, easy bruising of the skin, acne, high blood pressure, and psychological changes. Depending on the specific cause, doctors may treat this condition with surgery, radiation therapy, chemotherapy, or drugs that block the production of hormones.

Type 1 Diabetes

Type 1 Diabetes is usually diagnosed in children and young adults, and was previously known as juvenile diabetes. In Type 1 Diabetes, the body does not produce insulin. Insulin is a hormone that is needed to convert sugar (glucose), starches and other food into energy needed for daily life.

Type 1 Diabetes can cause long-term complications, including kidney problems, nerve damage, blindness, and early coronary heart disease and stroke.

Type 2 Diabetes

Unlike people with Type 1 Diabetes, people with Type 2 Diabetes produce insulin; however, either their pancreas does not produce enough insulin or the body cannot use the insulin adequately. This is called insulin resistance. When there isn’t enough insulin or the insulin is not used as it should be, glucose (sugar) can’t get into the body’s cells. When glucose builds up in the blood instead of going into cells, the body’s cells are not able to function properly.

Type 2 Diabetes is the more common type. Anyone can get Type 2 Diabetes. However, those at highest risk for the disease are those who are over 45, are obese or overweight, have had gestational diabetes, have family members who have Type 2 Diabetes, have prediabetes, are inactive, have low HDL cholesterol or high triglycerides levels or have high blood pressure.

Growth Hormone problems

Too much growth hormone in children who are still growing will make their bones and other body parts grow excessively, resulting in gigantism. This rare condition is usually caused by a pituitary tumor and can be treated by removing the tumor.

In contrast, when the pituitary gland fails to produce adequate amounts of growth hormone, a child’s growth in height is impaired. Hypoglycemia (low blood sugar) may also occur in kids with growth hormone deficiency, particularly in infants and young children with the condition.


Hyperthyroidism is a condition in which the levels of thyroid hormones in the blood are excessively high. Symptoms may include weight loss, nervousness, tremors, excessive sweating, increased heart rate and blood pressure, protruding eyes, and a swelling in the neck from an enlarged thyroid gland (goiter).


Hypothyroidism is when the levels of thyroid hormones in the blood are abnormally low. Thyroid hormone deficiency slows body processes and may lead to fatigue, a slow heart rate, dry skin, weight gain, constipation, and, in kids, slowing of growth and delayed puberty.

How Do Your Keep Your Endocrine System Healthy?

To keep your Endocrine system healthy, follow these 3 rules:

  1. Eat a healthy diet in order to maintain a healthy weight and balance hormones.

  2. Be aware of your family history. Monitor your endocrine system if endocrine disorders such as diabetes or hypothyroidism run in your family.

  3. Reduce stress to avoid extended chemical secretions that can result in disorders or a weakened immune system.

This article is part of a series called “Your Body: An Owner’s Manual” which explains how your body systems work and how to maintain them. The first article in the series included a picture of my wife, fitness coach Kathie Lamir, who exemplifies a healthy body. Pictures of Kathie were so well received that I have included one with each article in the series

Fitness Trainer Kathie Lamir

One thought on “The Endocrine System

Leave a Reply

Your email address will not be published. Required fields are marked *