Endocrine System > Adrenal Glands

Adrenal Steroids

The adrenal cortex is a factory for steroid hormones. In total, at least two to three dozen different steroids are synthesized and secreted from this tissue, but two classes are of particular importance:

Class of Steroid Major Representative Physiologic Effects
Na+, K+ and water homeostasis
Glucose homeostasis and many others

Additionally, the adrenal cortex produces some sex steroids, particularly androgens, a talent of considerable importance in such diseases as congenital adrenal hyperplasia.

Like all steroids, adrenal "corticosteroids" are synthesized from cholesterol through a series of enzyme-mediated transformations. The details of these pathways are presented elsewhere, but the major branches are easy to understand.

Each of the three major pathways involves sequential processing by a group of enzymes, some of which reside in endoplasmic reticulum and others inside mitochondria. Hence, synthesis involves shuttling of the steroids between these two organelles.

Synthesis of the different steroids is not uniformly distributed through the cortex. For example, the outermost group of cells (zona glomerulosa) synthesizes aldosterone, but essentially no cortisol or androgens because those cells do not express the enzyme 17-alpha-hydroxylase which is necessary for synthesis of 17-hydroxypregnenolone and 17-hydroxyprogesterone. That enzyme is however present in cells of the inner zones of the cortex (zonae fasiculata and reticularis), which are the major sites of cortisol production.

Like all steroid hormones, cortisol and aldosterone bind to their respective receptors, and the resulting hormone-receptor complexes bind to a hormone response element to modulate transcription of responsive genes. Although the physiologic effects of these two steroid hormones are distinctly different, their receptors are quite similar and, most interestingly, they bind to the same consensus response element in DNA! How then is it possible to get hormone-specific responses? Follow the path to the next topic to find out at least part of the answer.

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