The Anatomy of the Adrenal Gland

The adrenal glands (also known as suprarenal glands) release certain hormones that help the body function. The different hormones impact a range of functions, such as regulating heart rate, and blood pressure, helping the immune system, managing physical stress responses, and more. Certain medical disorders, like Cushing’s syndrome or Addison’s disease, cause the adrenal glands to produce too much or too little of their hormones.

Anatomy

The adrenal glands are two small, triangular-shaped glands that sit directly on top of the kidneys. The two major parts of the adrenal gland are the cortex and the medulla. The gland is surrounded by an adipose capsule, which acts as a protective barrier.

Adrenal Cortex

The cortex is the outer layer and is the largest part of the adrenal gland. It is divided into three zones—zona glomerulosa, zona fasciculata, and zona reticularis—all of which are responsible for producing different hormones.

• The zona glomerulosa is responsible for aldosterone (which regulates blood pressure).
• The zona fasciculata produces cortisol (used for stress and metabolism).
• The zona reticularis produces sex hormones testosterone and estrogen.

Adrenal Medulla

The medulla is the inner layer of the adrenal gland that makes a group of hormones called catecholamines. These are referred to as “fight or flight” hormones that help you respond to stress. One of the biggest hormones in this category is adrenaline (also known as epinephrine).

Anatomical Variations

In certain cases, there may be variations in the adrenal arteries, the arteries in the abdomen that are responsible for supplying blood to the adrenal glands. Typically the adrenal gland has input from three arteries on both the left side and right side. Past research has found that this isn’t always the case, as some individuals may have only four to five total artery inputs, or sometimes even less.

Variations of adrenal veins appear to be relatively common, having been found in 13% of cases of people undergoing removal of the adrenal gland. This can have significance during surgery. Normally, one central vein drains each adrenal gland, yet there are many variations.

Function

Hormones produced by the adrenal glands work together with other hormones of the endocrine system to regulate growth, the physical and chemical process of the metabolism, as well as sexual development and function. They do this by carrying specific hormones in the bloodstream directly to the areas and organs of the body that need them to function optimally.

Cortisol

Adrenal glands produce cortisol in response to signals from the pituitary gland (a pea-sized gland located in the brain just behind the bridge of the nose) as well as the hypothalamus (a small region near the base of the brain close to the pituitary gland). This interaction is often referred to as the hypothalamic–pituitary–adrenal axis (HPA axis).

For example, the hypothalamus will release a hormone called corticotropin-releasing hormone (CRH), and this tells the pituitary gland to secrete a separate hormone called adrenocorticotropic hormone (ACTH). ACTH is what stimulates the adrenal glands to make and release cortisol into the bloodstream. This process is regulated as the hypothalamus and pituitary gland monitor how much cortisol is in the blood and whether or not more is needed.

Aldosterone, Epinephrine, Norepinephrine

Other hormones produced by the adrenal glands work together to maintain proper functioning of the body:

• Adrenaline and noradrenaline hormones are secreted by the adrenal medulla and have effects such as increasing the heart rate, controlling blood flow throughout the body, and vasoconstriction (the constriction of blood vessels that can affect blood pressure).
• Aldosterone, produced in the zona glomerulosa part of the cortex, sends signals to the kidneys to absorb sodium and release potassium through urine, regulating blood pressure and the concentration of electrolytes in the body.

Associated Conditions

The most common conditions associated with adrenal glands happen when too much or too little hormones are produced. Adrenal glands can also be impaired if there’s a disorder in the pituitary gland, as it signals to the adrenal gland when to make certain hormones like cortisol and aldosterone.

Adrenal gland disorders include:

• Cushing’s syndrome
• Addison’s disease
• Pheochromocytoma
• Congenital adrenal hyperplasia
• Adrenal fatigue

Tests

There are several tests your healthcare provider can do to assess adrenal gland function, typically through blood and/or urine samples.

Some tests of the adrenal glands include:

• 17-Hydroxyprogesterone (or 17-OHP) test: This test is usually done as part of newborn screening in order to detect congenital adrenal hyperplasia. A heel prick blood sample is analyzed for 17-hydroxyprogesterone, which is created when cortisol is produced by the adrenal glands.
• Aldosterone test: With a sample of blood or urine, this test monitors how much aldosterone is in the body. An aldosterone test can diagnose adrenal fatigue or insufficiency, or a possible tumor in the adrenal glands. Benign adrenal gland tumors are very common, while adrenal cancer is rare, affecting 1 or 3 per 1 million people.
• Cortisol test: This test is used to look for signs of Cushing’s syndrome or Addison’s disease (when the adrenal glands make too much and too little cortisol, respectively). A blood draw is done twice during the day, once in the morning and another later in the day. Cortisol can also be measured with a 24-hour urine test (where you collect a day’s worth of urine and send it to a laboratory for analysis) or through saliva as a swab test (in certain instances).
• Dehydroepiandrosterone sulfate (DHEAS) test: DHEAS can be converted into sex hormones like estrogen and testosterone. A DHEAS blood test is done to help diagnose adrenal tumors, cancer, or sex hormone imbalances that may be affecting a person's development. In females, an imbalance may result in amenorrhea, hirsutism, or infertility, and males can have early puberty or infertility.