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Adrenal cortex
Gray1185.png
Layers of cortex.
Latin cortex glandulae suprarenalis
Gray's subject #277 1278
Precursor mesoderm[1 ]
Cortical part of the adrenal gland (on the pointer).

Situated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.

Contents

Layers

The cortex can be divided into three distinct layers of tissue based on their organisation. A special mnemonic to remember the layers is, "The layers get sweeter as you go deeper because G = salt, F = sugar, & R = sex, or GFR = salt, sugar, sex"

Layer Name Primary product
Most superficial cortical layer zona glomerulosa mineralocorticoids (eg, aldosterone)
Middle cortical layer zona fasciculata glucocorticoids (eg, cortisol)
Deepest cortical layer zona reticularis weak androgens (eg, dehydroepiandrosterone)

Notably, the reticularis in all animals is not always easily distinguishable and dedicated to androgen synthesis. In rodents, for instance, the reticularis also generates corticosteroids (specifically corticosterone, not cortisol). The two layers are collectively referred to as the fasciculo-reticularis. Female rodents also exhibit a another cortical layer called the "X zone" whose function is not yet clear.

Hormone synthesis

All adrenocortical hormones are synthesized from cholesterol. Cholesterol is transported into the inner mitochondrial membrane by steroidogenic acute regulatory protein (STAR), where it is converted into pregnenolone by the enzyme CYP11A1. Accordingly, production of hormones in all three layers of the adrenal cortex is limited by the transportation of cholesterol into the mitochondria and by its conversion into pregnenolone. Pregnenolone can be either dehydrogenated to progesterone, or hydroxylated to 17-alpha-hydroxypregnenolone.

The steps up to this point occur in many steroid-producing tissues. Subsequent steps to generate aldosterone and cortisol, however, primarily occur in the adrenal cortex:

  • Progesterone → (hydroxylation at C21) → 11-Deoxycorticosterone → (two further hydroxylations at C11 and C18) → Aldosterone
  • Progesterone → (hydroxylation at C17) → 17-alpha-hydroxyprogesterone → (hydroxylation at C21) → 11-Deoxycortisol → (hydroxylation at C11) → Cortisol

As the production of these hormone products is zone-dependent, so too is the distribution of the key enzymes involved in their synthesis. Aldosterone synthase expression is primarily limited to the glomerulosa while 17alpha-hydroxylase is absent from this layer. As noted above, this enzyme is also absent throughout the cortex of rodents. DHEA synthesis by the human reticularis depends on the absence of 3 beta-hydroxysteroid dehydrogenase.

Production

The adrenal cortex produces a number of different corticosteroid hormones.

Mineralocorticoids

They are produced in the zona glomerulosa. The primary mineralocorticoid is aldosterone. Its secretion is regulated by the oligopeptide angiotensin II (angiotensin II is regulated by angiotensin I, which in turn is regulated by renin). Aldosterone is secreted in response to high extracellular potassium levels, low extracellular sodium levels, and low fluid levels and blood volume. Aldosterone affects metabolism in different ways:

  • It increases urinary excretion of potassium ions
  • It increases interstitial levels of sodium ions
  • It increases water retention and blood volume

Glucocorticoids

They are produced in the zona fasciculata. The primary glucocorticoid released by the adrenal gland in the human is cortisol and corticosterone in many other animals. Its secretion is regulated by the hormone ACTH from the anterior pituitary. Upon binding to its target, cortisol enhances metabolism in several ways:

  • It stimulates the release of amino acids from the body
  • It stimulates lipolysis, the breakdown of fat
  • It stimulates gluconeogenesis, the production of glucose from newly-released amino acids and lipids
  • It increases blood glucose levels in response to stress, by inhibiting glucose uptake into muscle and fat cells
  • It strengthens cardiac muscle contractions
  • It increases water retention
  • It has anti-inflammatory and anti-allergic effects

Androgens

They are produced in the zona reticularis. The most important androgens include:

Pathology

See also

References

  1. ^ "Embryology of the adrenal gland". http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=endocrin.box.466. Retrieved 2007-12-11.  
  2. ^ Rainey WE, Nakamura Y (February 2008). "Regulation of the adrenal androgen biosynthesis". J. Steroid Biochem. Mol. Biol. 108 (3-5): 281–6. PMID 17945481.  

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