The downstream fate of pregnenolone will depend on the specific enzymes within that zone. Of note, ACTH induces steroidogenesis in all 3 zones by stimulating this rate-limiting enzyme. CYP11A1 catalyzes the rate-limiting step of steroid hormone production, and it is expressed in all three layers of the adrenal cortex. In the inner mitochondrial membrane, the cholesterol can then be converted to pregnenolone via CYP11A1 (cholesterol desmolase, or cholesterol side-chain cleavage, P450scc). Once cholesterol enters the cell, steroidogenic acute regulatory protein (StAR) regulates cholesterol transport from the outer mitochondrial membrane to the inner mitochondrial membrane. The zona glomerulosa produces mineralocorticoids, the zona fasciculata produces glucocorticoids, and the zona reticularis produces androgen precursors (mostly DHEA with some androstenedione). However, the specific steroid hormone produced differs in each layer because of zonal specific enzymes.
Each layer produces steroid hormones from the precursor cholesterol. It has 3 distinct functional and histological zones: the zona glomerulosa (outermost layer), the zona fasciculata (middle layer), and the zona reticularis (innermost layer).
The adrenal cortex takes part in steroidogenesis, producing glucocorticoids, mineralocorticoids, and androgen precursors.
Hence, this review highlights the physiological effects of diagnostic importance. In the diagnosis of disorders of the adrenal gland, a firm understanding of physiology is important given the different systems that regulate steroids. This brief article reviews the physiology of the adrenal gland and highlights the relevance of understanding the clinical syndromes of excess and deficiency. The cortex produces steroid hormones including glucocorticoids, mineralocorticoids, and adrenal androgens, and the medulla produces the catecholamines, epinephrine, and norepinephrine. The adrenal gland is made up of the cortex and medulla.
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