The adrenal glands are two small, pyramid-shaped organs, each roughly the size of a walnut, that sit perched on top of your kidneys. Despite their size, they produce hormones that touch almost every system in the body. Most Australians have heard of adrenaline, but the adrenal glands do far more than generate a fight-or-flight rush. They regulate your blood pressure, govern your response to prolonged stress, help maintain blood sugar levels, and even play a role in your body's salt and water balance.
The two distinct zones of the adrenal gland
Each adrenal gland is divided into two structurally and functionally separate parts: the outer cortex and the inner medulla. These two zones operate almost independently, with different cell types and different chemical outputs.
The adrenal cortex makes up about 80 per cent of the gland's volume. It produces steroid hormones derived from cholesterol, across three layers. The outermost layer, the zona glomerulosa, produces aldosterone, which tells the kidneys to retain sodium and excrete potassium, directly regulating blood pressure. The middle layer, the zona fasciculata, produces cortisol, the body's primary long-term stress hormone. The innermost cortical layer, the zona reticularis, produces androgens, which are weak sex hormones that contribute to libido and body hair in both sexes.
The adrenal medulla is functionally closer to a nerve cluster than a traditional gland. It releases adrenaline (epinephrine) and noradrenaline (norepinephrine) in response to acute stress signals sent from the brain's sympathetic nervous system. These hormones hit fast: heart rate climbs, blood vessels constrict, glucose floods the bloodstream, and non-essential functions like digestion shut down temporarily.
What cortisol actually does
Cortisol is probably the adrenal gland's most consequential product, and it's chronically misunderstood. It isn't simply a stress hormone to be minimised. Cortisol follows a daily rhythm, peaking shortly after you wake and declining through the day, coordinating closely with your body's circadian clock. If you want to understand why disrupted sleep wrecks so much more than just your energy levels, the cortisol-circadian relationship is a key part of the answer, and it connects directly to what circadian rhythm actually does to your health across every bodily system.
Cortisol suppresses inflammation, which is useful in short bursts but damaging when sustained. It raises blood sugar by triggering the liver to release stored glucose. It suppresses immune activity during the acute stress period. It also helps the body hold onto sodium, which is why chronic stress often tracks with elevated blood pressure. The full picture of what cortisol does to your body is considerably broader than the popular framing of it as something to simply reduce.
Aldosterone and blood pressure regulation
Aldosterone gets less attention than cortisol, but its job is just as consequential. When blood pressure falls or blood potassium rises, a cascade involving the kidneys, lungs, and adrenal cortex triggers aldosterone release. Aldosterone then acts on the kidneys to retain sodium, which draws water along with it and raises blood volume, pushing pressure back up. This system is called the renin-angiotensin-aldosterone system, and it's one of the body's primary blood pressure regulators. Many common blood pressure medications work by blocking different points in this pathway.
Primary hyperaldosteronism, where the adrenal glands produce too much aldosterone independent of normal signals, is now understood to be a more common cause of high blood pressure than previously recognised. Australian research groups have contributed significantly to revising the estimated prevalence upward over the past decade.
What happens when the adrenal glands malfunction
Adrenal disorders fall into two broad categories: overproduction and underproduction.
Adrenal insufficiency, where the glands produce too little cortisol and sometimes too little aldosterone, can be primary (Addison's disease, where the glands themselves are damaged) or secondary (where the pituitary gland fails to send the signal to produce cortisol). Addison's disease affects roughly 1 in 10,000 Australians. Symptoms include fatigue, low blood pressure, weight loss, and darkening of the skin in patches. Left unmanaged, an adrenal crisis, triggered by illness or surgery, can be life-threatening within hours.
Cushing's syndrome results from chronically excessive cortisol, most commonly from prolonged steroid medication use rather than an adrenal tumour. The physical signs include central weight gain, a rounded face, easy bruising, and slow wound healing. Internally, Cushing's drives insulin resistance, bone thinning, and immune suppression. It's rare from adrenal causes alone, with adrenal tumours producing cortisol independently occurring in only a handful of cases per million people each year.
Phaeochromocytoma is a tumour of the adrenal medulla that releases adrenaline and noradrenaline in unpredictable surges. Patients typically describe episodes of severe headache, sweating, rapid heart rate, and a sense of impending doom that arrive without warning. It's uncommon but worth knowing about because it's one of the treatable causes of hypertension that clinicians actively screen for in patients with difficult-to-control blood pressure.
How doctors test adrenal gland function
Blood and urine tests are the starting point. Serum cortisol is typically measured in the morning when levels should be at their peak. A 24-hour urinary cortisol collection gives a picture of overall output. Aldosterone and renin are measured together, because the ratio between them is what flags primary hyperaldosteronism rather than either value in isolation.
The ACTH stimulation test is the standard way to diagnose adrenal insufficiency. It involves injecting synthetic ACTH (the pituitary hormone that signals the adrenal glands to produce cortisol) and measuring the cortisol response 30 to 60 minutes later. A flat or blunted response confirms the glands aren't producing normally. Imaging with CT or MRI is used when a tumour or structural abnormality is suspected.
Supporting your adrenal glands without overstating the science
The wellness industry has built a substantial market around "adrenal support" supplements, and much of it outruns the evidence. Adrenal fatigue, the idea that chronic stress gradually exhausts the adrenal glands, isn't a recognised clinical diagnosis and isn't supported by the biochemistry. The glands don't tire out in healthy people. What does happen with chronic stress is a sustained dysregulation of the cortisol rhythm rather than true insufficiency.
Sleep quality is the single most evidence-backed lever for supporting healthy cortisol patterns. Consistent sleep timing, adequate duration, and minimising late-night light exposure all support a normal cortisol peak the following morning. Resistance training supports healthy cortisol metabolism over time. Chronic alcohol use disrupts aldosterone and cortisol regulation measurably. These aren't novel findings; they're the same lifestyle factors that appear across almost every endocrine system.
If you suspect an adrenal problem, a GP can run the relevant bloodwork. Self-diagnosing from a symptom list and reaching for a supplement stack is the least reliable route, and in the case of genuine adrenal insufficiency, it delays treatment that genuinely matters.