The endocrine system consists of numerous glands that produce molecules known as hormones, which are produced and released directly into the bloodstream. Where some glands in the body use ducts (tube-like structures) to release molecules, endocrine glands do not. When they release hormones it is done directly from the surface of the cells of the gland into the bloodstream. The released hormones can affect processes from reproduction, to thermal regulation, to heart rate, to sugar utilization and many more.
What Are the Glands of the Endocrine System?
- The pituitary gland and the pineal gland, both of which are located in the brain;
- the thyroid and parathyroid glands which are located in the neck;
- the thymus gland which is located in the upper margin of the thorax;
- the pancreas which is located near the stomach, gallbladder and liver;
- the adrenal glands which are located at the top of each of the kidneys; and finally
- the gonads, otherwise known as the ovaries and the testes.
What Do the Endocrine Glands Do?
These glands make and release hormones in response to numerous signals both from non-endocrine cells and tissues as well as from other endocrine glands with the goal of helping to maintain homeostasis of the body. Their functions are, in large part, heavily intertwined.
One good example of this is what is known as the hypothalamic-pituitary-adrenal axis. Signals received by the hypothalamus of the brain cause it to produce specific factors which are released into a specialized array of blood vessels which delivers them to the anterior lobe of the pituitary gland, which is located just below the hypothalamus. Once there they act to cause the release of pituitary hormones that then pass through the circulation and act on the adrenal gland.
The release of hormones, such as glucocorticoids like cortisol from the adrenal glands, is able to “feed-back” to the hypothalamus and pituitary to shut down their hormone release.
What Are the Major Functions Regulated by Endocrine Glands?
The pituitary gland, often referred to as the “master gland”, can regulate many different functions in the body from skeletal growth to milk production to uterine contractions during birthing.
The pineal gland produces melatonin which can regulate some of the body's physiological cycles.
The pancreas regulates the utilization or storage of carbohydrates through the release of insulin and glucagon. But the pancreas is also an “exocrine” gland, as other parts of it secrete enzymes important for digesting food.
The thymus gland plays a very important role in the development of the functioning immune system.
The thyroid gland can influence overall metabolism and also feedback to control the parathyroid glands which are critical to regulating calcium in the body.
The adrenal glands, which are divided into cortex and medulla regions, produce hormones such as epinephrine (adrenaline) and norepinephrine as well as steroid hormones such as cortisol and aldosterone which can regulate compounds circulating in the blood such as glucose and electrolytes.
The gonads produce the sex hormones such as estrogen and testosterone.
The process of maintaining the overall physiologic stability of the body (homeostasis) is heavily regulated by the endocrine glands and the hormones that they produce. There are numerous disorders related to the dysfunction of members of this group of glands including diabetes mellitus, Cushing’s syndrome, Grave’s disease, Addison’s disease and many others. The body relies on hormones every day to maintain good physiologic balance and function.
For more information on the endocrine system visit the National Cancer Institute pages of the US NIH.
 |
 |
