![]() ![]() The patterns of baseline cortisol synthesis across ages in humans have varied among reports ( 8, 15, 16). In addition, the HPA axis has been shown to become more sensitive to CRH stimulation and more resistant to dexamethasone suppression in elderly as compared with young adults ( 11-14). Several alterations in the hypothalamic-pituitary-adrenal (HPA) axis regulations have been reported with aging, including an elevated nocturnal nadir of adrenocorticotropic hormone (ACTH) and cortisol ( 7, 8), which affects sleep and memory function in the elderly ( 9, 10). ![]() Cortisol synthesis displays characteristic circadian rhythmicity, and its secretion is enhanced by a variety of stressors ( 5, 6). Cortisol synthesis is highly dynamic and tightly controlled by the hypothalamic-pituitary axis. The implications of aging on cortisol synthesis remain incompletely understood. With a reduction of the ZR and functional ZG with aging, we asked if the dimensions of the ZF are also altered across adulthood, either similarly with or disparately from its flanking zones. The evolution of the ZF across adult ages, however, has been minimally studied. The ZF is the largest cortical zone and the source of the single adrenal hormone essential for life. Age-related transformations also occur within the functional ZG: while the aldosterone synthase (CYP11B2)-expressing area is continuous in young individuals, this area decreases and becomes fragmented with aging ( 4). Reflecting these changes, the ZR displays a parallel involution with aging ( 2, 3). ![]() The most abundant adrenal androgen precursors, dehydroepiandrosterone and its sulfate, decline gradually after their peak in mid-20s, to concentrations approximately 5-fold lower by age 80 ( 1). The human adrenal cortex consists of three histologically distinct zones, each equipped with key enzymes for the productions of 3 major groups of steroid hormones: the outer zona glomerulosa (ZG) produces mineralocorticoids, such as aldosterone the intermediate zona fasciculata (ZF) produces glucocorticoids, particularly cortisol and the innermost zona reticularis (ZR) produces androgen precursors. Like other organs, the adrenal gland undergoes a series of morphological and functional changes with aging. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |