The adrenal cortex produces glucocorticoids (cortisol) and mineralocorticoids (aldosterone), with cortisol being central to the stress response. Cortisol is released from the zona fasciculata in response to ACTH from the anterior pituitary, which is stimulated by CRH from the hypothalamus during physical stress (trauma, hypoglycemia), emotional stress, or metabolic demands. Cortisol promotes gluconeogenesis and glucose mobilization, suppresses immune and inflammatory responses, and increases sympathetic nervous system sensitivity, preparing the body for "fight or flight." The hypothalamic-pituitary-adrenal (HPA) axis exhibits tight negative feedback: elevated cortisol inhibits CRH and ACTH release through actions on the hypothalamus and pituitary, preventing excessive stress hormone production.
Measure plasma cortisol (high in morning, low in evening) and ACTH in response to acute stressors (cold pressor test, mental arithmetic) and chronic stress. Study Cushing syndrome (excess cortisol) and Addison disease (cortisol deficiency). Understand dexamethasone suppression test for diagnosis.
Epinephrine is not produced by the adrenal cortex; it is produced by the adrenal medulla (derived from neural crest tissue) and is part of the sympathetic nervous system, not the endocrine axis.
When your body encounters a threat — whether it is a physical injury, a dangerous drop in blood sugar, or the psychological pressure of a high-stakes exam — it activates a hormonal cascade called the hypothalamic-pituitary-adrenal (HPA) axis. You already know from studying the hypothalamus-pituitary axis that the hypothalamus translates neural signals into hormonal commands, and that the anterior pituitary amplifies those commands by releasing tropic hormones into the bloodstream. The HPA axis is one of the most important specific instances of this general architecture: the hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the anterior pituitary to secrete adrenocorticotropic hormone (ACTH), which travels to the adrenal cortex and triggers release of cortisol from the zona fasciculata.
Cortisol is the body's primary long-duration stress hormone, and its effects are fundamentally metabolic. While the sympathetic nervous system you studied earlier provides the immediate "fight or flight" response — increased heart rate, dilated pupils, redirected blood flow — cortisol operates on a slower timescale of minutes to hours, ensuring the body has the fuel to sustain that response. It promotes gluconeogenesis in the liver, converting amino acids and glycerol into glucose. It breaks down muscle protein and adipose tissue to supply those substrates. It suppresses non-essential functions like immune surveillance and inflammation, which consume energy the body needs elsewhere during acute stress. Think of cortisol as the logistics officer behind the front lines: while epinephrine sounds the alarm, cortisol redirects supply chains to keep the fighting force operational.
The HPA axis is kept in check by negative feedback: when cortisol levels in the blood rise sufficiently, cortisol itself acts on receptors in both the hypothalamus and the anterior pituitary to suppress further CRH and ACTH release. This is the same feedback principle you learned in the endocrine system overview — the product of the cascade inhibits the cascade's own initiation. The result is a self-limiting loop: stress triggers cortisol release, cortisol addresses the metabolic demands of stress, and then rising cortisol levels shut down the axis to prevent overproduction. This feedback mechanism is so reliable that clinicians exploit it diagnostically: the dexamethasone suppression test administers a synthetic glucocorticoid and checks whether ACTH and cortisol fall appropriately. If they do not, the feedback loop is broken — a hallmark of conditions like Cushing syndrome.
When the HPA axis malfunctions, the consequences illustrate how precisely calibrated it must be. Cushing syndrome (chronic cortisol excess) produces hyperglycemia, muscle wasting, fat redistribution to the trunk and face, immune suppression, and osteoporosis — every one of cortisol's normal actions carried to a pathological extreme. Addison disease (cortisol deficiency) produces the mirror image: hypoglycemia, fatigue, weight loss, hypotension, and dangerous vulnerability to stress. These clinical bookends demonstrate that cortisol is not simply "the stress hormone" — it is a tightly regulated metabolic integrator whose value lies entirely in being produced in the right amount at the right time.