Zona reticularis

The adrenal gland is located on the upper segment of the kidney (Fig. 42-1). It consists of an outer cortex and an inner medulla. The adrenal medulla secretes the catecholamines epinephrine (also called adrenaline) and norepineprhine (also called noradrenaline), which are involved in regulation of the sympathetic nervous system. The adrenal cortex consists of three histologically distinct zones zona glomerulosa, zona fasciculata, and an innermost layer called the zona reticularis. Each zone is responsible for production of different hormones (Fig. 42-2). 

Adrenal steroid synthesis. The adrenal cortex consists of three histologically distinct zones the zona glomerulosa, zona fasciculata, and an innermost layer called the zona reticularis. Each zone is responsible for production of different hormones. (17 =... 

The zona reticularis produces the androgens androstene-dione, dehydroepiandrosterone (DHEA), and the sulfated form of dehydroepiandrosterone (DHEA-S). Only small amounts of testosterone and estrogen are produced in the adrenal glands. Androstenedione and DHEA are converted in the periphery, largely to testosterone and estrogen. 

The mammalian adrenal cortex is divided into three concentric zones the zona glomerulosa, zona fascicu-lata, and zona reticularis. The zona glomerulosa produces hormones, such as aldosterone, that are responsi-... 

Since the synthesis and release of cortisol are regulated by pituitary corticotrophin, removal of the pituitary gland results in decreased function and eventual atrophy of the zona fasciculata and zona reticularis. Infusion of supraphysiological concentrations of cortisol will suppress corticotrophin secretion from the pituitary and wUl markedly decrease circulating corticotrophin levels. This occurrence implies a negative feedback control for corticotrophin and corticosteroid release (Fig. 60.3). 

Mitotane (Lysodren) produces selective atrophy of the zona fasciculata and zona reticularis, which results in a decrease in the secretion of 17-hydroxy corticosteroids. Direct inhibition of cholesterol side-chain cleavage and 11 (3/18-hydroxylase activities has also been demonstrated. Mitotane is capable of inducing remission of Cushing s disease, but only after several weeks of therapy and at the price of severe gastrointestinal distress. Moreover, more than half of patients relapse following cessation of therapy. Other side effects include lethargy,... 

The adrenal gland, which is located at the cap of the kidney, is divided histologically into three zones the outer zone or zona glomerulosa, the middle zone or zona fasciculata, and the inner zone or zona reticularis. The adrenal cortex synthesizes cholesterol and pregnenolone through the interaction of a group of enzymatic reactions (Figure 61.1). 

The adrenal glands play an important role in pubertal development. Termed adrenarche, the maturation of a prominent zona reticularis, the innermost layer of the cortex, begins around age six to eight in girls, resulting in increased secretion of the adrenal androgens, dehydroepiandrosterone (DHEA) and DHEA sulfate (Beckman Feuston, 2003). The rise in these hormones leads to the development of pubic and axillary hair. Recent evidence suggests... 

In the adrenal cortex, the outermost zona glomerulosa secretes the mineralocorticoid aldosterone, and corticosterone. The middle zona fasciculata and the inner zona reticularis secrete predominately the glucocorticoids cortisol and corticosterone. In the human, the inner zona reticularis secretes large amounts of the adrenal androgens, DHEA and DHEAS, as well as cortisol [12]. Whereas steroidogenesis in the... 

Q1 Each adrenal gland is composed of an outer cortex and an inner medulla. The cortex consists of three layers where several steroid hormones, synthesized from cholesterol, are produced and secreted. The outer layer of the cortex, the zona glomerulosa, produces the mineralocorticoid aldosterone. The zona fasciculata lies under this layer and, together with the inner layer, the zona reticularis, secretes glucocorticoids, mainly cortisol, corticosterone and androgens. 

The zona fasciculata and zona reticularis produce and secrete 17a-hydroxypregnenolone, the main precursor of the adrenal androgens. A microsomal 17a-hydroxylase/ C-17,20-lyase (P-450ci7) enzyme converts 17a-... 

ACTH acts mainly on the cells of the zona fasciculata of the adrenal cortex to stimulate the synthesis and release of cortisol (Chapter 32). It also stimulates the secretion of adrenal androgens from the zona reticularis. Binding of ACTH to receptors activates formation of cAMP, which mediates cortisol formation and secretion and protein synthesis. Deficiency of ACTH leads to reduction in size and activity of adrenocortical cells in the inner two zones. 

DHEA sulfate (DHEAS) Cortex (zona reticularis) 200,000 100... 

The adrenal cortex, the zona reticularis in particular, daily secretes substantial amounts of DHEA and DHEAS, equaling or exceeding the amount of cortisol. Table 32-1 shows approximate blood levels of the important corticosteroids. Most of the DHEA and all of the DHEAS come from the adrenals. Negligible amounts of testosterone, dihydrotestosterone (DHT), and estradiol are secreted by the cortex however, DHEA and, to a lesser extent, DHEAS undergo conversion to estradiol in skeletal muscle and adipose tissue they also can be converted to testosterone. The adrenal cortex accounts for about two-thirds of the urinary 17-ketosteroids, which are a measure of androgen production. This steroidogenic versatility makes the adrenal cortex an important factor in certain disease states (see below). 

Cortisol is produced in the zona fasciculata and zona reticularis of the adrenal cortex, the end prixluct of a cascade of hormones which make up the hypothalamic-pituitary-adreniKortical axis (Fig. 2). Corticotrophin releasing hormone (CRH) is secreted by the hypothalamus under the influence of cerebral factors. Adrenocorticotrophic hormone (corticotrophin. orsimply ACTH) is secreted by the anterior pituitary under the control of CRH to maintain the fa.scicular and reticular zones of the adrenal cortex and to stimulate the secretion of cortisol. Ilypolhalamie secretion of CRH and pituitary secretion of ACTH are modulated by cortisol in negative feedback liwps. 

These glands are situated adjacent to the kidneys and have several distinct anatomical zones that are functionally different. The outer adrenal cortex has three distinct zones the outer zona glomerulosa, the intermediate zona fasciculate, and the inner zona reticularis, which adjoins the central adrenal medulla. 

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