Endocrinology, a branch of internal medicine, is the conventional field of study dealing with the endocrine system and its disorders. The Functional model of endocrinology, which focuses on underlying mechanisms that contribute to hormone imbalance, is growing rapidly.
The endocrine system regulates the body’s growth, metabolism, and sexual development and function. This is done through a group of glands that secrete hormones directly into the circulatory system for transportation to distant target organs.
The word endocrine means endo- “inside, within,” and krinein “to separate, distinguish.” The endocrine system is opposite to the body’s exocrine system, which secretes its hormones to the outside of the body using ducts, such as the sweat glands. The unique features of the endocrine glands include their ductless nature and their vascularity. The endocrine system’s major glands include:
The biochemical process, known as endocrine signaling, is what serves to regulate the body’s organs. The endocrine system is like a news network for the body that broadcasts hormonal messages to regulate bodily functions.
The effects of the endocrine system can last anywhere from a few hours up to weeks—in some cases it can be slow to initiate, and is often prolonged in response. In contrast, the nervous system rapidly sends information through electrical signaling, and the responses are often short-lived.
Endocrine signaling may take longer because the hormone takes more time to reach its target. The hormones are transported, principally through the bloodstream, to where they connect with target cells to induce a particular response. Consequently, endocrine signaling requires more time than neural signaling to excite a response in the target cells. It is essential to note that the precise response time varies with different hormones. For example, when a person confronts a frightening or shocking situation the hormones epinephrine and norepinephrine are released within milliseconds—this is known as the fight-or-flight response. In contrast, certain reproductive hormones may take up to 48 hours for target cells to respond.
The endocrine system’s feedback mechanisms maintain stable blood concentrations of hormones—the way a thermostat monitors and controls the temperature in a house. To make the conditions just right, the endocrine system uses two types of feedback: negative and positive. Negative feedback mechanisms, the most common type, attempts to maintain a target level. In contrast, positive feedback mechanisms attempts to increase away from a target level.
For example, in a negative feedback loop the following steps occur:
Every team needs some form of structure for messages to be delivered and received. Without modes of communication, orderliness can turn into chaos in a short period. Try to imagine how much work a medical scribe in a clinic would get done if they lost access to their laptop, email, and phone.
The hypothalamus, only about the size of a pearl, performs an integral role in determining what actions need to be taken by several endocrine glands in the body. Its principal purpose is to make sure that the body stays in a constant state of balance.
The hypothalamus resides in the central part of the brain. It observes the body through the circulatory and nervous systems, and efficiently links these systems to the endocrine system through the pituitary gland.
The pituitary gland is often called the master gland—it is a pea-sized gland located at the base of the skull in a bony pocket called the pituitary fossa, also known as the sella turnica.
Hormonal messages from the hypothalamus communicate with the anterior, or front, portion of the pituitary gland. The pituitary stalk has a unique arrangement of capillaries and veins, known as a portal system—this allows the hypothalamic hormones to access the anterior pituitary without circulating through the body.
There are two main components of the pituitary gland: the anterior pituitary, also called the adenohypophysis and the posterior pituitary, back portion, known as the neurohypophysis. Remember the two names by noting that the words anterior and adenohypophysis both start with the letter ‘A’.
The pineal gland is a small gland located deep inside the brain that secretes melatonin—often referred to as the third eye because its hormone release is dependent on how much light it “sees,” or detects, in the environment.
The body’s circadian rhythm, the day and night cycle, is regulated by melatonin; it is released at night with darkness and is inhibited by daylight.
The thyroid, a butterfly-shaped organ, and the parathyroid are a group of endocrine glands located at the base of the neck. These glands play a crucial role in supporting the body’s metabolism and free calcium levels.
Changes in thyroid hormones can lead to extreme changes in energy, growth and development, and reproduction. Calcium plays a vital role in sustaining healthy bones and teeth as well as the stimulation of muscle cells and neurons that are essential to the muscular, nervous, and cardiovascular systems.
The thyroid gland wraps around the front portion of the trachea and has two lateral lobes: left and right. The narrow medial region is called the isthmus.
The thyroid produces triiodothyronine (T3) and thyroxine (T4) by using iodine. Both T3 and T4 regulate a person’s metabolism by practically turning on each cell in the body and inducing them to produce proteins. The result includes increased heart rate, growth and development, energy consumption, and heat production.
There are four parathyroid glands, each the size of a grain of rice. Two parathyroid glands are on each lobe: (a) right superior and right inferior and (b) left superior and left inferior.
The thyroid gland also produces calcitonin, which works as an antagonist to the parathyroid hormone (PTH)—the only hormone produced by the parathyroid glands. These two work together to maintain a balance of calcium in the blood. PTH increases calcium levels by increasing the absorption in the intestine; reducing calcium elimination in the kidneys; and by raising the need for calcium in bones.
The pancreas secretes two essential hormones: insulin and glucagon. They come from the same parent organ but have complete opposite behaviors—insulin decreases the amount of sugar in your blood while glucagon makes it go up.
Located above each kidney are two triangular glands, known as the adrenal glands—sometimes called the suprarenal glands because they sit above the kidneys.
The adrenals are responsible for the regulation of electrolytes within the body as well as the secretion of numerous substances, including steroids, epinephrine, norepinephrine. The adrenal cortex secretes the steroids and the adrenal medulla secretes epinephrine and norepinephrine.
A typical example of the adrenal glands in action is the secretion of these substances during a fight-or-flight response when the blood pressure needs to be raised, energy needs to be sent to the muscles, and digestion needs to be slowed.
The reproductive glands are responsible for the secretion of sex hormones. In males, the testes, located in the scrotum, secrete hormones called androgens; the most significant of which is testosterone. Androgens affect various male characteristics, such as sexual development, the growth of facial hair and pubic hair as well as the production of sperm.
In females, the ovaries, located on either side of the uterus, produce estrogen and progesterone as well as eggs. These hormones affect female characteristics, for example, breast growth. They are also involved in reproductive roles such as menstruation and pregnancy.
The endocrine system is exquisitely self-regulating; it has powerful countermeasures that resist any interruption of the normal internal environment by internal or external factors. However, when this resistance is defeated, illness ensues.
The functional Medicine point of view is to determine what endocrine disruptor is contributing to poor health—these include: synthetic hormones, pesticides, chemicals, and other toxins that may block or impair normal endocrine functioning.
Full hormone panels are available for diagnosis of endocrine malfunctions.
Written by Sarah Gehrke, MSN, RN and last updated May 26, 2017
Last reviewed by Michael A. Tomeo MD on May 26, 2017