Adrenal gland and paraganglia

Author: Severino Rey Nodar, M.D., Ph.D. (see Authors page)

Revised: 13 January 2016, last major update August 2013

Copyright: (c) 2002-2016,, Inc.

PubMed Search: adrenal physiology[title]
Cite this page: Physiology. website. Accessed October 28th, 2016.
Definition / General
  • Adrenal cortex: synthesizes and secretes corticosteroids (mineralocorticoids, glucocorticoids and sex hormones), all derived from cholesterol
  • Zona glomerulosa (outer): produces mineralocorticoids (aldosterone - increases sodium and water absorption and potassium secretion)
  • Zona fasciculata (middle): produces glucocorticoids, some sex hormones
  • Zona reticularis (inner): produces estrogens and androgens, some glucocorticoids
  • Circulating low - density lipoproteins are internalized into cortical cells, lipoproteins are hydrolyzed, producing cholesterol esters, which break down to cholesterol and free fatty acids

    Cholesterol → 20 alpha hydroxycholesterol → (via 20, 22 desmolase complex)

          pregnenolone → progesterone - (21) → 11 deoxycorticosterone → corticosterone → aldosterone
             ↓(17)     ↓(17)
          17 alpha hydroxyprogesterone → (21) - deoxycortisol → cortisol
          dihydroxyepiandrosterone → androstenedione → estradiol 17 beta

  • 17: 17 hydroxylase
  • 21: 21 hydroxylase

  • Glucocorticoids: raise blood glucose level; anti-inflammatory and immunosuppressive; cortisol release almost entirely controlled by ACTH secretion from anterior pituitary, controlled by corticotropin-releasing hormone (CRH) secreted by hypothalamus
  • Mineralocorticoids: aldosterone targets renal distal tubule and stimulates re-uptake of sodium and potassium; aldosterone accounts for 90% of mineralocorticoid activity, also deoxycorticosterone, corticosterone, cortisol
  • Androgens: includes testosterone; excessive production causes premature puberty in young boys and masculine pattern of body hair in females

Adrenal medulla
  • Hormone production usually due to exercise, hypoglycemia, hemorrhage, stress
  • Preganglionic sympathetic nerve fibers pass from intermediolateral horn cells of spinal cord through sympathetic chains and splanchnic nerves, without synapsing, into adrenal medulla
  • Produce epinephrine (80%) and norepinephrine (20%), minimal amounts of dopamine, which are secreted into bloodstream and increase cardiac output and vascular resistance
  • Also produce chromogranin A, stored and secreted with epinephrine and norepinephrine
  • Physiologic effect is similar to sympathetic nervous stimulation

Extra - adrenal regulation
  • Hypothalamic corticotropin releasing hormone (CRH) enters hypophyseal portal system, reaches anterior pituitary gland and stimulates release of ACTH
  • ACTH travels in blood to adrenal cortex, is bound to cortical cell membranes and activates intracytoplasmic cyclases that form cAMP and GMP
  • Both cortisol and ACTH inhibit release of CRH, and cortisol also inhibits secretion of ACTH
  • ACTH normally is secreted episodically, with more and longer episodes in early morning and nadir in evening; this pattern causes circadian rhythm for cortisol seen in normals
  • Volume changes affect renin - angiotensin system, leading to aldosterone secretion
  • ACTH, potassium ions and aldosterone - stimulating factor also regulates aldosterone synthesis
  • Fetal adrenal gland lacks 3 beta hydroxysteroid dehydrogenase (converts pregnenolone to progesterone); as a result produces abundant dihydroepiandosterone, but little cortisol

Types of hormones
  • Autocrine: hormone binds to receptors on cell that produces it
  • Paracrine: hormone binds to receptors of nearby cells of a different type
  • Endocrine: hormone acts on target organs distant from site of synthesis
  • Hormones are either signaling molecules that interact with cell surface receptors or steroids that interact with intracellular receptors
  • Signaling molecules often act via second messengers, such as cAMP, inositol triphosphate or calcium levels