The adrenal cortex is the outer region and also the largest part of the adrenal gland. It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis. Each zone is responsible for producing specific hormones. It is also a secondary site of androgen synthesis.

Layers

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The adrenal cortex comprises three main zones, or layers that are regulated by distinct hormones as noted below. This anatomic zonation can be appreciated at the microscopic level, where each zone can be recognized and distinguished from one another based on structural and anatomic characteristics.

Zona glomerulosa

The outermost layer, the zona glomerulosa is the main site for the production of aldosterone, a mineralocorticoid. The synthesis and secretion of aldosterone are mainly regulated by the renin–angiotensin–aldosterone system. The zona glomerulosa cells express a specific enzyme aldosterone synthase (also known as CYP11B2). Aldosterone is largely responsible for the long-term regulation of blood pressure. Aldosterone's effects are on the distal convoluted tubule and collecting duct of the kidney where it causes increased reabsorption of sodium and increased excretion of both potassium (by principal cells) and hydrogen ions (by intercalated cells of the collecting duct).

The secretion of aldosterone is also stimulated by adrenocorticotropic hormone (ACTH).

The cells of the zona glomerulosa do not express 11β-hydroxylase and 17α-hydroxylase. This is the reason zona glomerulosa cannot synthesize cortisol, corticosterone, or sex hormones (androgens).

The expression of neuron-specific proteins in the zona glomerulosa cells of human adrenocortical tissues has been predicted and reported by several authors and it was suggested that the expression of proteins like the neuronal cell adhesion molecule (NCAM) in the cells of the zona glomerulosa reflects the regenerative feature of these cells, which would lose NCAM immunoreactivity after moving to the zona fasciculata. However, together with other data on neuroendocrine properties of zona glomerulosa cells, NCAM expression may reflect a neuroendocrine differentiation of these cells. The zona fasciculata has more 3β-hydroxysteroid dehydrogenase activity than the zona reticularis. Therefore, the zona fasciculata makes more 11-deoxycorticosterone, corticosterone, and cortisol.

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

thumb|Adrenal steroid hormone synthesis steps

Production

The adrenal cortex produces a number of different corticosteroid hormones.

Mineralocorticoids

The primary mineralocorticoid, aldosterone, is produced in the adrenocortical zona glomerulosa by the action of the enzyme aldosterone synthase (also known as CYP11B2). They play a role in numerous physiological responses including; metabolism, immune response, mood, cognitive functions, cardiovascular function, and reproduction. Glucocorticoids are also widely prescribed as medication to treat numerous conditions such as autoimmune diseases and lymphoproliferative diseases. The main glucocorticoid in humans is cortisol.

Androgens

They are produced mainly in the zona reticularis.

Pathology

thumb|Pathology of adrenal cortex

  • Adrenal insufficiency (e.g. due to Addison's disease)
  • Cushing's syndrome
  • Cushing's disease
  • Conn's syndrome
  • Adrenocortical carcinoma

See also

  • Adrenarche
  • Adrenopause

References

  • – "Posterior Abdominal Wall: Blood Supply to the Suprarenal Glands"