Tapering exogenous glucocorticoid has a dual function. Another well-accepted method of preventing long-term suppression of the HPA axis following glucocorticoid therapy is to slowly taper the dosage of exogenous glucocorticoids.
While there are no useful predictors to facilitate determining which patients are at risk for prolonged adrenal insufficiency, there is some evidence that alternate-day glucocorticoid treatment tends to preserve some adrenal function. Moreover, there are significant interindividual differences in these parameters. The time to recovery to full physiological function of the HPA axis is dependent on duration and dose of glucocorticoid treatment.
Such adrenal insufficiency after abrupt glucocorticoid withdrawal can be life threatening. Chronic suppression of the HPA axis by exogenous glucocorticoids also impacts on hypothalamic CRH and pituitary ACTH secretion and it may take some time to recover after cessation of glucocorticoid treatment. When prolonged corticosteroid treatment is stopped, the adrenal is atrophic and unresponsive and the patient is at risk for acute adrenal insufficiency. + +ĪCTH and CRH secretion are also inhibited by chronic pharmacologic treatment with exogenous corticosteroids in proportion to their glucocorticoid potency. These steroid hormones are low-molecular-weight lipid-soluble molecules able to diffuse freely across cell membranes. Zona fasciculata and zona reticularis cells secrete both glucocorticoids, primarily cortisol and corticosterone, and androgens such as dehydroepiandrosterone.
Zona reticularis cells are smaller than the other two types and are arranged in irregular cords or interlaced in a network. The zona reticularis, the innermost layer of the cortex, lies between the zona fasciculata and the adrenal medulla, accounting for only 7% of the mass of the adrenal gland. Zona fasciculata cells are polyhedral in shape and arranged in straight cords or columns, one or two cells thick, running at right angles to the capsule with capillaries between them. The zona fasciculata is the middle layer of the cortex. They secrete mineralocorticoids, primarily aldosterone. Zona glomerulosa cells are columnar or pyramidal in appearance and are arranged in closely packed, rounded, or arched clusters surrounded by capillaries. The zona glomerulosa is the outermost layer, situated immediately beneath the capsule.
The adrenal cortex can be subdivided into three concentric layers: zona glomerulosa, zona fasciculata, and zona reticularis ( Figure 21–2).
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