What Do the Adrenal Glands? (8 Functions)

What Do the Adrenal Glands? (8 Functions)

Clinically Reviewed by Dr. Andrew Stein MD, Consultant Physician. Last updated: April 2026

The adrenal glands are two small, triangle-shaped organs that sit on top of each kidney. Despite their small size, they are essential for survival.

They produce a variety of hormones that regulate your metabolism, immune system, blood pressure, and, most famously, your response to stress.

Anatomy: Cortex vs. Medulla

Each adrenal gland is composed of two distinct parts that function differently:

1. The Adrenal Cortex: The outer layer, which produces vital steroid hormones.

2. The Adrenal Medulla: The inner part, which produces non-essential (but highly important) hormones like adrenaline.

4 Functions of the Adrenal Cortex (Steroid Hormones)

The cortex produces three main types of hormones that manage long-term survival.

1. Regulating Metabolism (Cortisol)

Often called the “stress hormone,” cortisol helps the body manage energy. It controls how the body uses fats, proteins, and carbohydrates. It also suppresses inflammation and regulates the sleep-wake cycle.

2. Blood Pressure Control (Aldosterone)

The adrenal glands work closely with the kidneys to manage salt and water balance.

• Aldosterone signals the kidneys to absorb more sodium into the bloodstream and release potassium into the urine. This process regulates blood volume and maintains healthy blood pressure.

3. Immune System Suppression

Cortisol has a powerful anti-inflammatory effect. By regulating the immune response, the adrenal glands prevent the body from overreacting to threats, which is why synthetic cortisol (prednisone) is often used to treat autoimmune diseases.

4. Production of Sex Hormones (Androgens)

The adrenal cortex produces precursor hormones like DHEA and androgens. These are converted into estrogens (in women) and testosterones (in men) in other parts of the body, influencing secondary sexual characteristics and libido.

4 Functions of the Adrenal Medulla (The Stress Response)

The medulla is responsible for the “Fight or Flight” response, triggered during moments of acute physical or emotional stress.

5. The Fight-or-Flight Response (Adrenaline)

When you face a sudden threat, the medulla releases Adrenaline (Epinephrine). This hormone causes an immediate spike in energy, allowing you to react quickly to danger.

6. Increasing Heart Rate

Adrenaline and Noradrenaline act directly on the heart, increasing the heart rate and the force of contractions. This ensures that oxygen-rich blood reaches your muscles as fast as possible.

7. Redirecting Blood Flow

During stress, the adrenal glands cause blood vessels to constrict in non-essential areas (like the skin and digestive system) and dilate in essential areas (like the lungs and skeletal muscles).

8. Rapid Glucose Release

The medulla triggers the liver to release stored glucose (sugar) into the bloodstream. This provides an instant “fuel injection” for the brain and muscles during an emergency.

Common Adrenal Disorders

When the adrenal glands produce too much or too little of these hormones, it can lead to serious health issues:

• Addison’s Disease: Occurs when the adrenal cortex does not produce enough cortisol or aldosterone. Symptoms include fatigue, low blood pressure, and skin darkening.

• Cushing’s Syndrome: Caused by an overproduction of cortisol, leading to weight gain (especially in the face and upper back), high blood pressure, and fragile skin.

• Pheochromocytoma: A rare tumour of the adrenal medulla that causes “bursts” of adrenaline, leading to dangerous spikes in heart rate and blood pressure.

Summary: Adrenal Hormones at a Glance