Steroid nucleus definition

Cells of the zona fasciculata and zona reticularis lack aldosterone synthase (CYP11B2) that converts corticosterone to aldosterone, and thus these tissues produce only the weak mineralocorticoid corticosterone. However, both these zones do contain the CYP17A1 missing in zona glomerulosa and thus produce the major glucocorticoid, cortisol. Zona fasciculata and zona reticularis cells also contain CYP17A1, whose 17,20-lyase activity is responsible for producing the androgens, dehydroepiandosterone (DHEA) and androstenedione. Thus, fasciculata and reticularis cells can make corticosteroids and the adrenal androgens, but not aldosterone.

Because steroids are lipophilic, they diffuse easily through the cell membranes, and therefore have a very large distribution volume. In their target tissues, steroids are concentrated by an uptake mechanism which relies on their binding to intracellular proteins (or " receptors ", see below). High concentration of steroids are also found in adipose tissue, although this is not a target for hormone action. In the human male, adipose tissue contains aromatase activity, and seems to be the main source of androgen-derived estrogens found in the circulation. But most of the peripheral metabolism occurs in the liver and to some extent in the kidneys, which are the major sites of hormone inactivation and elimination, or catabolism (see below).

Enteroendocrine cells have traditionally been recognized by their affinity for certain metal stains, hence the older terms chromaffin cells (having an affinity for chromium) and argentaffin cells or argyrophil cells (having an affinity for silver).  With sufficient resolution, these cells can sometimes be recognized in routine light microscopic preparations by their relatively pale cytoplasm with a broad base and a basal concentration of secretory vesicles (in contrast to the apical concentration of secretory vesicles for exocrine serous cells or mucous cells ).  Immunocytochemical methods are preferred for demonstrating and properly identifying the various types of enteroendocrine cells.

Steroid nucleus definition

steroid nucleus definition


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