Synthesis of Corticosteroids See

Formation of active corticosteroids in each zone of the adrenal cortex involves a series of transformations 

Diagrammatic representation of zone-specific steroid synthesis in the adrenal cortex. All three zones can convert cholesterol into pregnenolone, but because of the presence/absence of certain enzymes, the flow of pregnenolone is preferentially directed to the synthesis of the steroid for which the particular zone is specific. It has not been determined whether the zona fasciculata produces dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) in physiologically significant amounts. 

Cortisol biosynthesis by mitochondrial and endoplasmic reticulum enzymes of the adrenal cortex. The rate-limiting step in steroidogenesis is the importation of cholesterol from cytoplasm to mitochondria which is mediated by the steroidogenic acute regulatory protein (StAR). 

The adrenal cortex, the zona reticularis in particular, daily secretes substantial amounts of DHEA and DHEAS, equaling or exceeding the amount of cortisol. Table 32-1 shows approximate blood levels of the important corticosteroids. Most of the DHEA and all of the DHEAS come from the adrenals. Negligible amounts of testosterone, dihydrotestosterone (DHT), and estradiol are secreted by the cortex however, DHEA and, to a lesser extent, DHEAS undergo conversion to estradiol in skeletal muscle and adipose tissue they also can be converted to testosterone. The adrenal cortex accounts for about two-thirds of the urinary 17-ketosteroids, which are a measure of androgen production. This steroidogenic versatility makes the adrenal cortex an important factor in certain disease states (see below). 

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