Figure 2022

Electron micrograph of cells in the zona fasciculata. The boundary between adjacent cells of the cord is indicated by the arrowheads. Lipid droplets (L) are numerous (the lipid has been partially extracted), x 15,000. Inset. A higher magnification of an area in the cell at the top of the micrograph reveals the extensive sER that is characteristic of steroid-secreting cells. Portions of the Golgi apparatus are also evident. x40,000.

ing interleukin-l (IL-1 ) and IL-2 production by lymphocytes and macrophages. Glucocorticoids also stimulate destruction of lymphocytes in lymph nodes and inhibit mitosis by transformed lymphoblasts. Cells of the zona fasciculata also secrete small amounts of gonadocorticoids, principally androgens.

ACTH regulates secretion of the zona fasciculata

The secretion and production of glucocorticoids and sex steroids by the zona fasciculata is under feedback control of the CRH-ACTH system. ACTH is necessary for cell growth and maintenance and also stimulates steroid synthesis and increases blood flow through the adrenal gland. Exogenous ACTH maintains the structure and function of the zona fasciculata after hypophysectomy. In animals, administration of ACTH causes hypertrophy of the zona fasciculata.

Circulating glucocorticoids may act directly on the pituitary gland, but they most commonly exert their feedback control on neurons in the arcuate nucleus of the hypothalamus, causing the release of CRH into the hypothalamo-hyophyseal portal circulation. Evidence also suggests that circulating glucocorticoids and the physiologic effects that they produce stimulate higher brain centers that, in turn, cause the hypothalamic neurons to release CRH.

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