HPA Axis

The Adrenal Glands

  • The adrenal glands are triangular shaped organs that sit on top of the kidneys.
  • Each adrenal gland is composed of an outer portion called the cortex, and an inner portion called the medulla.
  • The adrenal cortex secretes mineralocorticoids, glucocorticoids, and androgens.
  • The cortex is further divided into three layers, or zones: glomerulosa (outer layer), fasciculata (middle layer), and reticularis (inner layer).
  • The innermost portion of the adrenal gland, the adrenal medulla, secretes catecholamines and is under the direct influence of the sympathetic nervous system.
  • Catecholamines: epinephrine and norepinephrine

The Adrenal Cortex (G-F-R)

ZonaPositionHormone ClassHormonesDeeper = Sweeter
GlomerulosaOuter layerMineralocorticoidAldosteroneSalt
FasciculataMiddle layerGlucocorticoidCortisolSugar
ReticularisInner layerAndrogenDHEA, DHEA-S, androstenedioneSex

Hypothalamic-pituitary-adrenal Axis

  • The hypothalamic-pituitary-adrenal (HPA) axis is a major neuroendocrine system that involves the hypothalamus, pituitary gland, and the adrenal glands.
  • Corticotropin-releasing hormone (CRH)
  • Stress response
  • Released from hypothalamus
  • Stimulates the release of adrenocorticotropic hormone (ACTH)
  • ACTH
  • Released from anterior pituitary
  • Stimulates the release of cortisol
  • Cortisol
  • Released from adrenal gland (zona fasciculata of adrenal cortex)
  • Provides negative feedback, acting on the hypothalamus and pituitary to suppress CRH and ACTH production