Adrenal Gland – Anatomy, Function, Hormones, and Disorders   Recently updated !

The adrenal gland is a small endocrine gland that sits on top of each kidney and produces hormones that regulate metabolism, blood pressure, stress responses, immune function, electrolyte balance, and reproduction. Although each gland weighs only a few grams, together they play a critical role in maintaining homeostasis. The adrenal glands produce more than 50 hormones and hormone precursors, including cortisol, aldosterone, adrenaline (epinephrine), noradrenaline (norepinephrine), and adrenal androgens. Disorders affecting these glands can have profound effects on nearly every organ system.

Key Takeaways: Adrenal Gland

• The adrenal gland is an endocrine gland located above each kidney.
• Humans normally have two adrenal glands, one on each side of the body.
• Each gland has two functionally distinct regions:
  • Adrenal cortex (outer layer): Produces steroid hormones.
  • Adrenal medulla (inner core): Produces catecholamines.
• The adrenal glands regulate stress responses, metabolism, blood pressure, electrolyte balance, and aspects of reproduction.
• Major hormones include cortisol, aldosterone, epinephrine, norepinephrine, and adrenal androgens.
• Adrenal gland disorders include Addison disease, Cushing syndrome, primary hyperaldosteronism, congenital adrenal hyperplasia, pheochromocytoma, and adrenal cancer.
• Because adrenal hormones affect many organs simultaneously, adrenal diseases often cause a wide variety of symptoms.

Why the Adrenal Glands Are Important

The adrenal glands are essential because they produce hormones that allow the body to adapt to changing conditions. Without adequate adrenal function, maintaining normal blood pressure, blood sugar, and electrolyte balance becomes impossible.

Important roles include:

• Regulating blood pressure through aldosterone
• Controlling blood glucose during fasting and stress
• Managing the body’s response to illness and injury
• Maintaining sodium and potassium balance
• Supporting normal immune function
• Influencing inflammation
• Helping regulate metabolism of carbohydrates, fats, and proteins
• Producing hormones involved in puberty and sexual development
• Initiating the “fight-or-flight” response

People cannot survive for long without cortisol and aldosterone replacement if both adrenal glands stop functioning.

History of the Study of the Adrenal Glands

The adrenal glands have fascinated anatomists and physicians for centuries.

Some important milestones include:

The discovery of adrenal hormones revolutionized endocrinology and transformed treatment for inflammatory diseases and adrenal insufficiency.

What Is an Adrenal Gland?

The adrenal gland is a paired endocrine gland positioned on the superior pole of each kidney. Despite its location, it functions independently of the kidneys.

Each gland contains two embryologically and functionally different endocrine organs:

• Adrenal cortex (outer portion)
• Adrenal medulla (inner portion)

These regions produce completely different classes of hormones.

The adrenal cortex synthesizes steroid hormones from cholesterol.

The adrenal medulla produces catecholamines from the amino acid tyrosine.

Anatomy of the Adrenal Gland

Appearance

The adrenal glands are yellowish because of their high lipid content.

Typical characteristics include:

• Length: 4–6 cm
• Width: 2–3 cm
• Thickness: about 1 cm
• Weight: 4–6 grams each

The right gland is typically:

• Pyramid-shaped
• Slightly smaller

The left gland is usually:

• Crescent-shaped
• Slightly longer

These differences reflect surrounding anatomy rather than function.

Number

Most people have:

• Two adrenal glands
• One above each kidney

Rarely, people are born with accessory adrenal tissue or an extra adrenal gland.

Location

The adrenal glands lie in the retroperitoneal space.

They rest:

• Superior to the kidneys
• Beneath the diaphragm
• Within the protective perirenal fat

The right adrenal gland lies close to:

• Inferior vena cava
• Liver

The left adrenal gland lies near:

• Spleen
• Stomach
• Pancreas
• Aorta

Structure

The adrenal gland consists of an outer cortex and inner medulla.

Adrenal Cortex

The cortex accounts for about 90% of the gland.

It has three layers.

Adrenal Medulla

The medulla contains specialized chromaffin cells.

These cells produce:

• Epinephrine
• Norepinephrine
• Small amounts of dopamine

Chromaffin cells are modified sympathetic neurons.

Blood Supply

The adrenal glands have one of the richest blood supplies of any organ relative to their size.

They receive blood from three main arteries:

• Superior suprarenal artery
• Middle suprarenal artery
• Inferior suprarenal artery

Thousands of tiny arteries enter the gland.

Venous drainage differs between sides:

• Right adrenal vein drains directly into the inferior vena cava.
• Left adrenal vein drains into the left renal vein.

The unusually rich blood supply enables rapid hormone release into circulation.

Are There Differences Between Men and Women?

The adrenal glands are nearly identical in size and structure in men and women.

However, hormone production differs slightly.

Women generally produce:

• Slightly greater relative importance of adrenal androgens
• DHEA contributes to pubic and axillary hair development.

Men rely primarily on testosterone from the testes, so adrenal androgens contribute less overall.

During pregnancy, maternal adrenal hormone production increases substantially to support fetal development and metabolism.

Functions of the Adrenal Gland

The adrenal gland coordinates long-term hormonal regulation and rapid emergency responses.

Its hormones influence virtually every organ system.

Cortisol

Cortisol:

• Raises blood glucose
• Increases protein breakdown
• Helps metabolize fat
• Suppresses excessive inflammation
• Supports immune regulation
• Helps maintain blood pressure
• Increases during physical and psychological stress

Aldosterone

Aldosterone regulates:

• Sodium retention
• Potassium excretion
• Blood volume
• Blood pressure

It acts primarily on the kidneys.

Adrenal Androgens

The adrenal cortex produces:

• DHEA
• DHEA sulfate (DHEA-S)
• Androstenedione

These hormones:

• Contribute to puberty
• Support libido
• Provide precursors for testosterone and estrogen

Epinephrine and Norepinephrine

These hormones produce the classic fight-or-flight response.

Effects include:

• Increased heart rate
• Elevated blood pressure
• Dilated airways
• Increased blood sugar
• Increased blood flow to muscles
• Reduced digestive activity

Their effects occur within seconds.

Hormonal Regulation: The HPA Axis

The adrenal cortex does not work independently. It is part of the hypothalamic-pituitary-adrenal (HPA) axis, one of the body’s major endocrine control systems.

1. The hypothalamus releases corticotropin-releasing hormone (CRH).
2. The anterior pituitary gland releases adrenocorticotropic hormone (ACTH).
3. ACTH stimulates the adrenal cortex to produce cortisol.
4. Rising cortisol levels suppress CRH and ACTH through negative feedback.

Aldosterone is regulated primarily by the renin-angiotensin-aldosterone system (RAAS) and blood potassium levels rather than ACTH.

Embryology and Development

The adrenal gland has an unusual developmental origin because its two major regions arise from different embryonic tissues.

• The adrenal cortex develops from mesoderm.
• The adrenal medulla develops from neural crest cells, the same cells that give rise to parts of the sympathetic nervous system.

During fetal development, the adrenal glands are proportionally much larger than they are in adults. A temporary fetal cortex produces steroid hormones important for placental estrogen production. This fetal zone rapidly shrinks after birth.

The cortex continues to mature throughout childhood, while the zona reticularis develops later and begins producing increasing amounts of adrenal androgens before puberty in a process called adrenarche.

Adrenal Gland Disorders

Addison Disease (Primary Adrenal Insufficiency)

The adrenal glands fail to produce sufficient cortisol and often aldosterone.

Common causes include:

• Autoimmune disease
• Tuberculosis
• Infection
• Metastatic cancer
• Genetic disorders

Symptoms include:

• Fatigue
• Weight loss
• Low blood pressure
• Salt craving
• Hyperpigmentation
• Low blood sugar

Untreated Addison disease can lead to an adrenal crisis, a life-threatening medical emergency.

Secondary Adrenal Insufficiency

This condition results from inadequate ACTH production by the pituitary gland rather than damage to the adrenal glands themselves.

Common causes include:

• Pituitary disease
• Long-term corticosteroid therapy followed by abrupt withdrawal

Unlike primary adrenal insufficiency, aldosterone production is usually preserved.

Cushing Syndrome

Cushing syndrome results from prolonged excess cortisol.

Causes include:

• Corticosteroid medications
• ACTH-producing pituitary tumors (Cushing disease)
• Adrenal tumors

Symptoms include:

• Central obesity
• Round (“moon”) face
• Buffalo hump
• Purple stretch marks
• Muscle weakness
• Diabetes
• Osteoporosis
• High blood pressure

Primary Hyperaldosteronism (Conn Syndrome)

Excess aldosterone causes:

• High blood pressure
• Low potassium
• Muscle weakness
• Excessive thirst
• Frequent urination

Congenital Adrenal Hyperplasia (CAH)

Inherited enzyme deficiencies impair cortisol production.

The most common form involves deficiency of 21-hydroxylase.

Effects may include:

• Salt wasting
• Low cortisol
• Excess androgen production
• Ambiguous genitalia in affected female infants
• Early puberty

Pheochromocytoma

A pheochromocytoma is a tumor of adrenal medulla chromaffin cells.

It releases excessive catecholamines, causing:

• Episodic high blood pressure
• Sweating
• Headaches
• Palpitations
• Anxiety

Although uncommon, it is an important cause of secondary hypertension.

Adrenal Tumors and Cancer

Many adrenal tumors are benign and discovered incidentally during imaging for unrelated conditions. These are called adrenal incidentalomas.

Some tumors produce excess hormones, while others are hormonally inactive.

Adrenocortical carcinoma is rare but often aggressive.

Symptoms of Adrenal Gland Dysfunction

Symptoms depend on whether hormone production is too low or too high.

Low hormone production may cause:

• Chronic fatigue
• Weakness
• Weight loss
• Dizziness
• Salt craving
• Nausea
• Low blood pressure

Excess hormone production may cause:

• High blood pressure
• Weight gain
• Anxiety
• Sweating
• Rapid heartbeat
• High blood sugar
• Easy bruising
• Muscle weakness
• Excess hair growth in women

Because these symptoms overlap with many other medical conditions, laboratory testing is usually needed to diagnose adrenal disorders.

How Doctors Evaluate Adrenal Function

Diagnosis often combines hormone testing with medical imaging.

Common tests include:

• Blood cortisol levels
• ACTH levels
• Aldosterone and renin measurements
• DHEA-S levels
• Plasma or urine metanephrines (for pheochromocytoma)
• ACTH stimulation (cosyntropin) test
• Dexamethasone suppression test

Imaging studies may include:

• CT scans
• MRI
• PET scans in selected cases

Tips for Adrenal Gland Health

Healthy adrenal glands depend on overall health rather than special supplements or “detoxes.”

Evidence-based recommendations include:

• Get adequate sleep.
• Eat a balanced diet.
• Stay physically active.
• Manage chronic stress with healthy coping strategies.
• Maintain healthy blood pressure.
• Follow prescribed steroid medication instructions carefully.
• Never stop long-term corticosteroid medications abruptly without medical supervision.
• Seek prompt medical care for symptoms of adrenal disease.

There is no scientific evidence that “adrenal fatigue” supplements restore adrenal function in healthy people.

Adrenal Glands in Other Animals

All mammals possess adrenal glands with cortex and medulla regions that closely resemble those of humans.

Birds, reptiles, and amphibians also produce corticosteroids and catecholamines, although the organization of adrenal tissue may differ and is often less distinctly separated into cortex and medulla.

Fish have the same hormone systems but usually lack discrete adrenal glands. Instead, steroid-producing cells (interrenal tissue) and catecholamine-producing chromaffin cells are distributed near the kidneys. These tissues are considered evolutionarily homologous to the mammalian adrenal gland.

The remarkable conservation of adrenal hormones across vertebrates highlights their importance in regulating stress responses, metabolism, salt balance, and cardiovascular function.

Common Misconceptions

Myth: The adrenal glands only produce adrenaline.
Fact: Most adrenal hormones are steroid hormones produced by the cortex, including cortisol and aldosterone.

Myth: Stress permanently wears out the adrenal glands.
Fact: Chronic stress affects hormone regulation, but it does not normally “exhaust” healthy adrenal glands.

Myth: Adrenal fatigue is a recognized medical diagnosis.
Fact: Major endocrine organizations do not recognize adrenal fatigue as a distinct medical condition. Symptoms attributed to it often have other explanations or require evaluation for genuine adrenal disease.

Myth: The adrenal glands are part of the kidneys.
Fact: They sit on top of the kidneys but are separate endocrine organs with different functions.

Myth: Removing one adrenal gland always requires lifelong hormone replacement.
Fact: In many cases, the remaining healthy adrenal gland can produce enough hormones for normal function.

Frequently Asked Questions

How many adrenal glands do humans have?

Most people have two, one above each kidney.

Can you live without your adrenal glands?

Yes, but only with lifelong hormone replacement therapy. Without replacement, loss of both adrenal glands is life-threatening.

Which hormone is most important?

Several are essential, but cortisol and aldosterone are critical for survival.

Are the adrenal glands part of the nervous system?

No. They are endocrine glands, although the adrenal medulla functions as a specialized extension of the sympathetic nervous system.

What causes an adrenaline rush?

Stress, fear, excitement, exercise, or danger activates the sympathetic nervous system, stimulating the adrenal medulla to release epinephrine and norepinephrine.

Do adrenal glands shrink with age?

Some structural changes occur with aging, including gradual thinning of parts of the cortex, but the glands generally continue functioning throughout life.

Can stress damage the adrenal glands?

Ordinary psychological stress does not damage healthy adrenal glands, although severe illness, autoimmune disease, infection, bleeding, or tumors can impair adrenal function.

Interesting Facts About the Adrenal Glands

• The adrenal glands receive one of the highest rates of blood flow per gram of tissue in the body.
• The adrenal cortex and medulla arise from different embryonic tissues and function as two distinct endocrine organs within the same gland.
• Epinephrine was the first hormone isolated in pure form.
• The fetal adrenal glands are proportionally much larger than adult adrenal glands.
• During extreme stress, adrenal hormone production can increase dramatically within minutes.
• The right and left adrenal glands have different shapes but perform the same functions.

Glossary

• ACTH: Pituitary hormone that stimulates cortisol production.
• Adrenal cortex: Outer steroid-producing region of the adrenal gland.
• Adrenal medulla: Inner catecholamine-producing region.
• Aldosterone: Hormone regulating sodium, potassium, and blood pressure.
• Catecholamines: Hormones including epinephrine and norepinephrine.
• Chromaffin cells: Specialized cells that produce catecholamines.
• Cortisol: Major glucocorticoid involved in metabolism and stress responses.
• DHEA: An adrenal androgen and precursor to sex hormones.
• Endocrine gland: An organ that releases hormones into the bloodstream.
• HPA axis: The hypothalamic-pituitary-adrenal hormonal feedback system.
• RAAS: The renin-angiotensin-aldosterone system that regulates blood pressure and fluid balance.

References

• Marieb, E.N.; Hoehn, K. (2012). Human Anatomy & Physiology (9th ed.). Pearson. ISBN 978-0-321-74326-8.
• Melmed, S.; Polonsky, K.S.; Larsen, P.R.; Kronenberg, H.M. (2011). Williams Textbook of Endocrinology (12th ed.). Saunders. ISBN 978-1-4377-0324-5.
• Miller, W.L.; Auchus, R.J. (2011). “The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders”. Endocrine Reviews. 32 (1): 81–151. doi:10.1210/er.2010-0013
• Ross, M.; Pawlina, W. (2011). Histology: A Text and Atlas (6th ed.). Lippincott Williams & Wilkins. pp. 708, 780. ISBN 978-0-7817-7200-6.
• Santulli, G. (2015). Adrenal Glands: From Pathophysiology to Clinical Evidence. Nova Science Publishers, New York, NY. ISBN 978-1-63483-570-1.