What do the adrenal glands do?
The adrenals are two small glands sitting on top of the kidneys. Their outer layer (cortex) makes cortisol, aldosterone and DHEA; their core makes adrenaline. Adrenaline is released within seconds, cortisol rises over 20 to 40 minutes.
Choose a situation: the cross-section of the gland shows which layer is working, and the curve follows the hormones minute by minute.
- Glomerulosa: aldosterone
- Fasciculata: cortisol
- Reticularis: DHEA
- Medulla: adrenaline
Simplified curves, as a percentage of the starting level. Time runs 60 times faster.
Where are the adrenals?
One on each kidney, each weighing about 4 to 5 grams. They have two parts that have nothing in common: the cortex, which makes hormones from cholesterol, and the core (medulla), wired directly to the nerves (Dutt, 2023).
What does each layer make?
| Layer | Hormone | Main role |
|---|---|---|
| Glomerulosa (outside) | Aldosterone | Keeping salt and water, holding blood pressure |
| Fasciculata | Cortisol | Releasing sugar from stores, regulating inflammation, daily rhythm |
| Reticularis | DHEA | A small source of sex hormones |
| Medulla (core) | Adrenaline, noradrenaline | Immediate response: heart, breathing, sugar |
Why is adrenaline faster than cortisol?
Adrenaline is already made and stored: a nerve gives the order, it comes out within seconds. Cortisol goes through a chain (hypothalamus, pituitary, then adrenal) and must be made on demand. In a review of 208 studies, it peaks 21 to 40 minutes after the start of a stress (Dickerson and Kemeny, 2004).
Why does cortisol rise on waking?
In the 30 to 45 minutes after waking, cortisol rises by 50% on average, sometimes much more. This is the cortisol awakening response, which helps you get going (Fries, 2009).
Frequently asked questions
Does "adrenal fatigue" exist?
It is not a recognized diagnosis: a review of all published studies found no evidence that it exists (Cadegiani and Kater, 2016). True adrenal insufficiency (Addison's disease) does exist, but it is rare and is diagnosed with a blood test.
Does coffee make the adrenals work?
Caffeine slightly increases adrenaline and cortisol, especially in people who do not usually drink it. See the page on coffee.
Why is cortisol low in the evening?
It follows a clock: high in the morning, low early in the night. This is what makes room for melatonin and sleep.
Does chronic stress wear out the adrenals?
The glands do not wear out like an engine. But lasting stress can disrupt the cortisol rhythm, which becomes flatter across the day. A flat rhythm goes with poorer health, according to 80 studies (Adam, 2017).
See also
The stress of an oral exam A 24-hour day Coffee
Sources
- Dickerson SS, Kemeny ME. Acute stressors and cortisol responses: a theoretical integration and synthesis of laboratory research. Psychol Bull. 2004;130(3):355-91. PMID 15122924
- Fries E, Dettenborn L, Kirschbaum C. The cortisol awakening response (CAR): facts and future directions. Int J Psychophysiol. 2009;72(1):67-73. PMID 18854200
- Dutt M, Wehrle CJ, Jialal I. Physiology, Adrenal Gland. StatPearls. 2023. PMID 30725945
- Lam J, et al. Anatomy, Abdomen and Pelvis: Adrenal Glands. StatPearls. 2022. NCBI Bookshelf
- Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocr Disord. 2016;16(1):48. DOI 10.1186/s12902-016-0128-4
- Adam EK, et al. Diurnal cortisol slopes and mental and physical health outcomes: a systematic review and meta-analysis. Psychoneuroendocrinology. 2017;83:25-41. PMC5568897