¶ adrenal gland
The adrenal glands are paired endocrine organs sitting atop the kidneys, comprising two distinct functional zones: the outer cortex (producing steroid hormones including cortisol, aldosterone, and sex hormones) and inner medulla (producing catecholamines adrenaline and noradrenaline). They are the final effector organs of both HPA axis and sympathetic nervous system stress responses.
The adrenal cortex has three zones: zona glomerulosa (aldosterone for fluid/electrolyte balance), zona fasciculata (cortisol for metabolic stress response), and zona reticularis (DHEA and sex hormone precursors). Cortisol synthesis is stimulated by ACTH from pituitary, which is released in response to CRH from hypothalamus. The adrenal medulla contains chromaffin cells that release adrenaline (80%) and noradrenaline (20%) directly into bloodstream upon sympathetic nervous system activation. Both systems converge on adrenal glands, providing dual-axis stress response: fast sympathetic (seconds-minutes) via catecholamines, slow HPA (minutes-hours) via cortisol.
The adrenal glands are central integration point for stress responses and represent final common pathway for HPA axis and SNS activation. Chronic stress can lead to adrenal dysfunction (though true 'adrenal fatigue' is controversial—typically reflects central HPA axis dysregulation rather than gland failure). Clinical assessment must evaluate both axes: cortisol rhythm (HPA axis), catecholamine response (SNS), and synchronization between them. Desynchronization of HPA-SNS rhythms is hallmark of chronic stress and metabolic disease. Supporting adrenal function requires addressing upstream regulation (hypothalamic inflammation, circadian disruption) not just supplementing with adaptogenic herbs. Cortisol and catecholamines have profound effects on immune function, metabolism, and behavior.
- Adrenal cortex produces cortisol (zona fasciculata), aldosterone (zona glomerulosa), DHEA (zona reticularis)
- Adrenal medulla produces adrenaline (80%) and noradrenaline (20%)
- Final effector organ for both HPA axis (cortisol) and SNS (catecholamines)
- ACTH from pituitary stimulates cortisol synthesis
- Sympathetic nerve fibers directly innervate adrenal medulla chromaffin cells
- Cortisol and catecholamines must be synchronized in circadian rhythm for health
- Desynchronization of HPA-SNS is hallmark of chronic stress and metabolic disease
- True adrenal insufficiency (Addison's disease) is rare; most 'fatigue' is central HPA dysregulation
- Cortisol has mineralocorticoid receptor affinity in addition to glucocorticoid receptor
- Chronic catecholamine exposure causes receptor desensitization and resistance
- HPA axis — adrenal cortex is final effector organ of HPA axis releasing cortisol in response to ACTH
- sympathetic nervous system — sympathetic nerves directly innervate adrenal medulla triggering catecholamine release
- cortisol — cortisol is synthesized in adrenal zona fasciculata in response to ACTH stimulation
- adrenaline — adrenaline is produced by adrenal medulla chromaffin cells (80% of medullary output)
- noradrenaline — noradrenaline comprises 20% of adrenal medulla output and is sympathetic neurotransmitter
- ACTH — ACTH from pituitary stimulates adrenal cortex to synthesize and release cortisol
- CRH — CRH from hypothalamus initiates HPA axis cascade culminating in adrenal cortisol release
- aldosterone — aldosterone is produced by adrenal zona glomerulosa regulating sodium/potassium balance
- DHEA — DHEA is produced by adrenal zona reticularis as precursor to sex hormones
- chronic stress — chronic stress disrupts adrenal function through HPA axis dysregulation and catecholamine resistance
- circadian rhythm — adrenal cortisol and catecholamine release must follow synchronized circadian rhythm
- glucocorticoid receptor — cortisol from adrenal glands binds to glucocorticoid receptors throughout body modulating gene expression
- mineralocorticoid receptor — aldosterone (and high cortisol) binds mineralocorticoid receptors affecting fluid/electrolyte balance
- immune system — adrenal hormones (cortisol, catecholamines) profoundly modulate immune cell function and trafficking
- inflammation — cortisol from adrenals suppresses inflammation through multiple mechanisms including NF-κB inhibition
- metabolism — adrenal hormones regulate glucose, protein, and fat metabolism during stress response
- hypothalamus — hypothalamus controls adrenal cortex function via CRH release and SNS controls medulla
- pituitary gland — pituitary ACTH directly stimulates adrenal cortex cortisol synthesis
- adaptogenic — adaptogenic herbs (Rhodiola, Ashwagandha) modulate adrenal output by affecting central HPA regulation
- insulin resistance — chronic cortisol excess from adrenals promotes insulin resistance and visceral adiposity