An Overview of the Adrenal Glands

Beyond Fight or Flight

Adrenal Gland Essentials

The adrenal glands are two glands that sit on top of your kidneys that are made up of two distinct parts.

  • The adrenal cortex—the outer part of the gland—produces hormones that are vital to life, such as cortisol (which helps regulate metabolism and helps your body respond to stress) and aldosterone (which helps control blood pressure).
  • The adrenal medulla—the inner part of the gland—produces nonessential (that is, you don’t need them to live) hormones, such as adrenaline (which helps your body react to stress).
 
When you think of the adrenal glands (also known as suprarenal glands), stress might come to mind. And rightly so—the adrenal glands are arguably best known for secreting the hormone adrenaline, which rapidly prepares your body to spring into action in a stressful situation.
 
But the adrenal glands contribute to your health even at times when your body isn’t under extreme stress. In fact, they release hormones that are essential for you to live.
 
Anatomy of the Adrenal Glands
The adrenal glands are two, triangular-shaped organs that measure about 1.5 inches in height and 3 inches in length. They are located on top of each kidney. Their name directly relates to their location (ad—near or at; renes—kidneys).
 
Each adrenal gland is comprised of two distinct structures—the outer part of the adrenal glands is called the adrenal cortex. The inner region is known as the adrenal medulla.
 
Hormones of the Adrenal Glands
The adrenal cortex and the adrenal medulla have very different functions. One of the main distinctions between them is that the hormones released by the adrenal cortex are necessary for life; those secreted by the adrenal medulla are not.
 
 Adrenal Cortex Hormones
The adrenal cortex produces two main groups of corticosteroid hormones—glucocorticoids and mineralcorticoids. The release of glucocorticoids is triggered by the hypothalamus and pituitary gland. Mineralcorticoids are mediated by signals triggered by the kidney.
 
 When the hypothalamus produces corticotrophin-releasing hormone (CRH), it stimulates the pituitary gland to release adrenal corticotrophic hormone (ACTH). These hormones, in turn, alert the adrenal glands to produce corticosteroid hormones.
 
Glucocorticoids released by the adrenal cortex include:
  • Hydrocortisone: Commonly known as cortisol, it regulates how the body converts fats, proteins, and carbohydrates to energy. It also helps regulate blood pressure and cardiovascular function.
  • Corticosterone: This hormone works with hydrocortisone to regulate immune response and suppress inflammatory reactions.
 
The principle mineralcorticoid is aldosterone, which maintains the right balance of salt and water while helping control blood pressure.
 
There is a third class of hormone released by the adrenal cortex, known as sex steroids or sex hormones. The adrenal cortex releases small amounts of male and female sex hormones. However, their impact is usually overshadowed by the greater amounts of hormones (such as estrogen and testosterone) released by the ovaries or testes.
 
Adrenal Medulla Hormones
Unlike the adrenal cortex, the adrenal medulla does not perform any vital functions. That is, you don’t need it to live. But that hardly means the adrenal medulla is useless. The hormones of the adrenal medulla are released after the sympathetic nervous system is stimulated, which occurs when you’re stressed. As such, the adrenal medulla helps you deal with physical and emotional stress. You can learn more by reading a SpineUniverse article about the sympathetic nervous system.
 
You may be familiar with the fight-or-flight response—a process initiated by the sympathetic nervous system when your body encounters a threatening (stressful) situation. The hormones of the adrenal medulla contribute to this response.
 
Hormones secreted by the adrenal medulla are:
  • Epinephrine: Most people know epinephrine by its other name—adrenaline. This hormone rapidly responds to stress by increasing your heart rate and rushing blood to the muscles and brain. It also spikes your blood sugar level by helping convert glycogen to glucose in the liver. (Glycogen is the liver’s storage form of glucose.)
  • Norepinephrine: Also known as noradrenaline, this hormone works with epinephrine in responding to stress. However, it can cause vasoconstriction (the narrowing of blood vessels). This results in high blood pressure.
 
Disorders and Diseases of the Adrenal Glands
There are multiple reasons why the adrenal glands might not work as they should. The problem could be with the adrenal gland itself, or the root cause may be due to a defect in another gland.
 
Below are the most common disorders and diseases of the adrenal glands:
  • Addison’s disease: This rare disorder may affect anyone at any age. It develops when the adrenal cortex fails to produce enough cortisol and aldosterone. To learn more, read our article about Addison's Disease.
  • Adrenal cancer: Adrenal cancer is an aggressive cancer, but it’s very rare. Malignant adrenal tumors are rarely confined to the adrenal glands—they tend to spread to other organs and cause adverse changes within the body because of the excess hormones they produce. To learn more, read our article about adrenal cancer.
  • Cushing’s syndrome: Cushing’s syndrome is an uncommon condition that is essentially the opposite of Addison’s disease. It is caused by overproduction of the hormone cortisol. There are a variety of causes of this disorder—a tumor in the adrenal gland or pituitary gland could be to blame. To learn more, read our article about Cushing's syndrome.
  • Congenital adrenal hyperplasia: This genetic disorder is characterized by low levels of cortisol. It’s common for people with congenital adrenal hyperplasia to have additional hormone problems such as low levels of aldosterone (which maintains a balance of water and salt). 
The adrenal glands have a multi-functional role in the endocrine system. The two very different parts of these glands, the medulla and cortex, regulate and maintain many of your internal processes—from metabolism to the fight-or-flight response.