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Cortisol Production: The HPA Axis & Stress Response

Cortisol (hydrocortisone) is the primary glucocorticoid, synthesized in the adrenal cortex (zona fasciculata) under HPA axis control.

HPA Axis Regulation

  1. Hypothalamus: Releases CRH (corticotropin-releasing hormone) in response to stress, circadian rhythm (suprachiasmatic nucleus), cytokines.
  2. Anterior Pituitary: CRH → corticotrophs release ACTH (adrenocorticotropic hormone).
  3. Adrenal Cortex: ACTH → MC2R → cAMP → StAR protein → cholesterol → pregnenolone → cortisol (via 17α-hydroxylase, 21-hydroxylase, 11β-hydroxylase).
  4. Negative Feedback: Cortisol inhibits CRH (hypothalamus) and ACTH (pituitary). Ultradian pulsatility (hourly pulses) + circadian rhythm (peak ~8 AM, nadir ~midnight).

Stimuli for Cortisol Release

CategoryExamples
Psychological StressAnticipatory anxiety, public speaking, cognitive challenge, trauma reminders.
Physical StressSurgery, trauma, burns, sepsis, hypoglycemia, intense exercise, heat/cold.
MetabolicFasting, hypoglycemia, insulin-induced hypoglycemia (ITT test).
Immune/InflammatoryCytokines (IL-1, IL-6, TNF-α) → stimulate HPA at all levels.
CircadianAwakening response (CAR: 50–160% ↑ in 30–60 min post-wake).

Physiological Actions

  • Metabolic: ↑Gluconeogenesis (liver), ↑proteolysis (muscle), ↑lipolysis (adipose) → fuel for brain/immune cells.
  • Anti-inflammatory/Immunosuppressive: ↓NF-κB, ↓cytokines, ↓immune cell trafficking/function.
  • Cardiovascular: ↑Vascular tone (permits catecholamine action), ↑cardiac output.
  • CNS: Modulates mood, cognition, fear, memory (hippocampus).
  • Fluid/Electrolyte: Weak mineralocorticoid effect (↑Na⁺ retention, K⁺ excretion at high doses).

Clinical Disorders

  • Cushing's Syndrome: Chronic excess (ACTH-dependent: pituitary adenoma, ectopic; ACTH-independent: adrenal tumor).
  • Adrenal Insufficiency (Addison's): Primary (adrenal destruction), secondary (pituitary), tertiary (hypothalamic/steroid withdrawal).
  • Dysregulation: Chronic stress → flattened diurnal slope, blunted CAR → metabolic syndrome, depression, immune dysfunction.

Cortisol is the essential stress hormone; its dynamic regulation is vital for survival.

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