ENDO 101: Everything You (Should) Want to Know About Endocrinology

By Mary Green

Chances are that if you’re reading this article, you’re in a medical office reception area or a doctor’s exam room. And odds are better than even that you are there to be seen by an endocrinologist , a physician who specializes in the diagnosis and treatment of a wide range conditions affecting the endocrine system including diabetes, thyroid disorders, growth hormone deficiency, infertility, cholesterol problems, hypertension, obesity and more.

Even for some under the care of an endocrinologist, the medical specialty can be something of a mystery. So, here’s a primer to help promote understanding of this vital area of clinical practice.

The word endocrinology is from the Greek words endon, meaning "within" and krīnō, meaning "to separate" and is a branch of medicine that deals with the endocrine system’s glands, the actions of their hormones and the metabolic consequences. The endocrine system’s glands and organs secrete hormones that regulate a number of vital functions of our body. Although every organ system in the body secretes and responds to hormones, endocrinology focuses primarily on the endocrine glands whose primary function is hormone secretion. These include the hypothalamus, pineal, pituitary, thyroid, parathyroid, adrenals,

pancreas, testes and ovaries .

Hormones have many different functions and modes of action and often affect different parts of the body in different ways. For example, the male sex hormone testosterone is responsible for sex drive, but also impacts muscle size and encourages the growth of pubic, facial or body hair. There are up to 40 different hormones circulating in your blood at any time. Once released into the bloodstream, a hormone circulates throughout the body until it reaches its specific target -- or targets -- to perform its function. These targets can be either other endocrine glands or other organs and tissues in the body.

While all these glands normally coordinate with each other exceptionally well in order to regulate various metabolic processes, hormonal function is a balancing act of sorts. Too much or too little of one hormone can have an impact on the release of other hormones. If this hormonal imbalance occurs, some of your body’s systems do not work properly. In order to bring the hormones back to their normal levels, your body has built-in mechanisms to keep track of and respond to any changes by means of a complex, but highly efficient, feedback system that links some endocrine glands with others. A hormonal imbalance typically is corrected by the body by "feeding" some of its hormones (and sometimes other hormones) from the target back to the original endocrine gland.

This "tells" the endocrine gland to release more or less of the hormone, and the balance is restored.

When this system goes awry and there appears to be a problem, a patient is usually referred by his/her primary care physician to an endocrinologist, who is an expert in treating frequently complex (and often chronic) conditions which can involve several different systems within the body.

Endocrinologists perform diagnostic tests to evaluate the problem, determine a course of treatment and counsel patients on lifestyle changes that can improve the medical condition(s). This type of specialist needs extensive knowledge of clinical chemistry and biochemistry to understand the physiology and chemical processes underlying endocrine disorders. Many endocrinologists also are involved in clinical research to gain a better understanding of endocrine disease and to assist in the development of better treatment options. Some endocrinologists treat a range of endocrine disorders, while others choose to specialize in a single category such as diabetes, infertility or pediatrics.

While certain disorders are clearly within the domain of endocrinologists, others can involve the endocrinology system even though they don’t originate there. In these cases, the endocrinologist may work with an internist, primary care physician or a specialist in another discipline to coordinate the patient’s follow-up care.

In order to become an endocrinologist, one must first complete medical school, advanced training during three to four years of a residency program, and a minimum of two years’, but often three years’, further sub-specialization in a fellowship before seeking required certification from the American Board of Internal Medicine.

Because endocrinology encompasses so many conditions and diseases, there is great demand from patients for information. For that reason, the American Association of Clinical Endocrinologists (www.aace.com) and its educational, scientific and charitable arm, the American College of Endocrinology (ACE), have created an in-depth patient information website which features educational materials covering a broad range of endocrine conditions; a “Find an Endocrinologist” feature where the public can locate endocrinologists by geographic region and/or specialty; valuable tips on how to charge of your health; and online issues of this magazine. Visit www.empoweryourhealth.org to learn more about endocrine conditions or www.aace.com to learn more about endocrinologists and AACE, the world’s largest association of clinical endocrinologists, with over 7,000 members in the U.S. and abroad.

Anatomy of the Endocrine System

The endocrine system consists of a collection of small glands that regulate a number of vital functions of our body. All these glands coordinate with each other in order to regulate various life processes. Here is a rundown of the endocrines glands that form this system and their functions.

Adrenal glands (suprarenal glands)

Located atop the kidneys, adrenal glands are just two or three inches long and weigh less than an ounce, but are responsible for the secretion of more than 35 different hormones which maintain the body’s salt and water balance, affect kidney function and help the body cope with and respond to stress. During stressful situations, adrenaline is released by the adrenals and proteins are converted into energy by the cortisol released from the cortex of these glands, leading to the release of the body’s stored sugar. This substance is known as glycogen, and it generates energy that accelerates our heart, respiratory rate and blood pressure. In this way, our body gets the fuel required for the quick response in a crisis. The adrenal glands also produce androgens, male sex hormones that promote the development of male characteristics, and estrogen, which is an essential hormone for female body metabolism.


The hypothalamus, located just above the brain stem, serves as the link between the endocrine system and the nervous system via the pituitary gland by controlling the pituitary through the stimulation or suppression of hormone secretions. It activates and controls involuntary functions such as body temperature, hunger, thirst and fatigue.

Pituitary gland

No larger than the size of a pea, the pituitary is often referred to as the “master” gland because it secretes hormones that regulate the function of other endocrine glands (the thyroid, adrenals and reproductive glands). It also produces hormones that stimulate the growth of bones and tissues, affect sexual development, encourage reabsorption of water by the kidneys and even trigger uterine contractions during and after labor.

Pineal body (pineal gland)

Located deep in the center of the brain, the pineal gland is involved in several body functions, including secretion of the hormone melatonin, which helps maintain a person’s wake/ sleep cycles and regulate reproductive hormones and the conversion of nervous system signals to endocrine signals.


Located in the abdomen, the pancreas is both a digestive organ and an endocrine gland. The “islets of Langerhans” are the regions of the pancreas that contain its hormone-producing cells. The two primary endocrine functions of these cells are to keep the body supplied with fuel for energy by maintaining a steady level of the glucose (sugar) in the bloodstream with the hormones insulin and glucagon and to help in food digestion by secreting digestive enzymes.

Parathyroid glands

Each the size of a grain of rice, the body’s four parathyroid glands have a very rich blood supply, which comes in handy since they monitor the calcium level in the blood. Calcium is the element that allows the normal conduction of electrical currents along nerves—it’s how our nervous system works, how one nerve 'talks' to the next, and is the primary element which causes muscles to contract. As blood filters through the parathyroids, they detect the amount of calcium and make more parathyroid hormone (PTH) when calcium levels are too low. Once the PTH is released, it circulates to the cells of the bones and causes them to release calcium into the bloodstream. When calcium levels are too high, the parathyroids make less PTH or cease producing it until normal levels are restored. The parathyroids also help the lining of the intestines become more efficient at absorbing calcium in the diet.

Thyroid gland

The butterfly-shaped thyroid takes iodine and converts it into two hormones (T3 and T4), which are transported throughout the body and enter cells to regulate blood pressure, body temperature, heart rate, metabolism and how the body reacts to other hormones. The thyroid gland also produces calcitonin, which stimulates bone cells to add calcium to bone, as well as regulating calcium metabolism.


The ovaries, the female gonads, have two main reproductive functions in the body: they produce oocytes (eggs) for fertilization and the reproductive hormones estrogen and progesterone. Estrogen is involved in the development of female sexual features such as breast growth, the accumulation of body fat around the hips and thighs, and the growth spurt that occurs during puberty. Both estrogen and progesterone are also involved in the regulation of the menstrual cycle and prepare the lining of the uterus for pregnancy in the event of the released egg being fertilized.


The testes, also known as testicles or male gonads, have two functions: to produce sperm and to produce hormones, particularly testosterone, which regulate body changes associated with sexual development, including enlargement of the penis, the growth spurt that occurs during puberty, and the appearance of other male secondary sex characteristics such as deepening of the voice, growth of facial and pubic hair, and the increase in muscle growth and strength.