What are the 3 Most Important Zones for Steroid Hormones Synthesis?

Steroid Hormones – Adrenal Cortical Hormones

Adrenal Cortical Hormones

Free Online Lectures of Biochemistry for Medical, Dental and Allied Health Sciences by Biochemistry Club

The Adrenal Cortex has 3 different zones for the production of different classes of steroid hormones.

  1. The smallest and outermost zona glomerulosa produces the C21 steroids, mineralocorticoids. They have effects on water & electrolyte balance.
  2. The middle zone of the adrenal cortex, the zona fascicularis produces the glucocorticoids mainly; adrenal androgens and, estrogens to a lesser extent
  3. The innermost zona reticularis produces the androgens (C19) & estrogens (C18)

Synthesis of Steroid Hormones

  • Cholesterol is first acted upon by desmolase and a 6-carbon unit is cleaved off, forming the 21-Carbon steroid, Pregnenolone.
  • Pregnenolone is a common precursor for all the steroid hormones.
  • This is the rate limiting step for synthesis of all steroid hormones.
  • Adrenocorticotropic hormone (ACTH) stimulates this step.
  • Progesterone is the first steroid hormone formed from pregnenolone in two steps.
  • The β-hydroxyl group is converted to a keto group by a 3-beta-oldehydrogenase & the Δ5 double bond shifted to Δ4.
  • Progesterone is further converted into glucocorticoids, mineralocorticoids and sex steroids.
  • The major adrenal glucocorticoids are cortisolcortisone and corticosterone.
  • The major mineralocorticoid is aldosterone, but 11-deoxycorticosterone and corticosterone also have significant mineralocorticoid activity.
  • These reactions are affected by hydroxylation.
  • These specific hydroxylases are mono-oxygenases. (All these enzymes are NADPH dependent).
  • The ACTH stimulates the synthesis of all steroid hormones by activating desmolase so that the availability of pregnenolone is increased.

All these lectures are organized and listed in detail in their proper sections. To view these lessons please visit the Hormones & Signal Transduction Section. This can be approached by directly clicking the Biochemistry II button or it can also be approached from the drop down menu in Biochemistry II tab. Once you reach the section click the curriculum tab to view the full list in the section.

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