Zona fasciculata

Glucocorticoids are secreted by the cells of the zona fasciculata in the adrenal cortex. Hydrocortisone is the most important, and regulates intermediary metabo-... 

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 =... 

Other Systemic Effects. Mild nonspecific endocrine lesions were observed after inhalation exposure to 1,2-dibromoethane. After subchronic exposure to 75 ppm, rats had adrenal lesions consisting of swelling and/or cytoplasmic vacuolization of cells in the zona fasciculata of the cortex and thyroid lesions consisting of slight decreases in follicular size. Degenerative changes in the adrenal cortex occurred at elevated incidence in female Fischer 344 rats after chronic exposure to 40 ppm... 

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,... 

Adrenals Rat Atrophic zona fasciculata 0.05% in drinking-water 21-60 days Szabo etal. (1976)... 

Silver is cleared from the system via the liver (Furchner et al. 1968 Scott and Hamilton 1950). Deposition of uncleared silver can occur along the renal glomerular basement membrane (Creasey and Moffat 1973 Danscher 1981 Ham and Tange 1972 Moffat and Creasey 1972) and mesangium (Day et al. 1976), and in the Kupffer cells and the sinusoid endothelium cells of the liver (Danscher 1981). Silver has also been detected intra- and extracellularly in the skin and mucosa of the tongue, in the chromaffin cells, cells of the zona glomerulosa, and zona fasciculata of the adrenal glands, and in the exocrine and endocrine sections of the pancreas (Danscher 1981). 

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). 

Steroid hormones are produced in the adrenal cortex and the sex glands. All such hormones originate from cholesterol. Figure 16.4 shows the overall scheme for steroid hormone biosynthesis that is applicable to all tissues. The final products may be divided into the following groups mineralocorticoids (e.g., aldosterone), produced by the zona glomerulosa of the adrenal cortex glucocorticoids (e.g., cortisol), produced by the zona fasciculata of the adrenal cortex and the... 

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... 

Calcium, via calmodulin, also activates cyclic AMP phosphodiesterases which inactivate cyclic AMP by metabolism to AMP. Inhibition of phosphodiesterase yields a small increase in ACTH-stimulated steroidogenesis [2], This is relatively slight in the adrenocortical zona fasciculata-reticularis cell, which has a low phosphodiesterase level the zona glomerulosa cell has a higher activity [60,61], which may result from higher level of activation of the calcium/calmodulin intracellular messenger system in the zona glomerulosa. 

The adrenal cortex (AC) produces the glucocorticoid cortisol (hydrocortisone) in the zona fasciculata and the mineralocorticoid aldosterone in the zona glomerulosa. Both steroid hormones are vitally important in adaptation responses to stress situations, such as disease, trauma, or surgery. Cortisol secretion is stimulated by hypophyseal ACTH aldosterone secretion by angiotensin II in particular (p. 128). In AC failure (primary adrenocortical insuf ciency, Addison disease), both cortisol and aldosterone must be replaced when ACTH production is deficient (secondary adrenocortical insuf ciency), cortisol alone needs to be replaced. Cortisol is effective when given orally (30 mg/day, 2/3 a.m 1 /3 p.m.). In stress situations, the dose is raised 5- to 10-fold. Aldosterone is poorly effective via the oral route instead, the mineralocorticoid fludrocortisone (0.1 mg/day) is given. 

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 paraventricular nucleus of the hypothalamus releases corticotrophin-releasing hormone, which stimulates the pituitary gland to release adrenocorticotropin (ACTH). ACTH travels via the blood to the adrenal gland, where it stimulates the release of cortisol. Cortisol is secreted by the cortex of the adrenal gland from a region called the zona fasciculata in response to ACTH. Elevated levels of cortisol exert negative feedback on the pituitary, which decreases the amount of ACTH released from the pituitary gland. 

Two neuropeptides, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) are released from parvoceUular neurons in the hypothalamic PVN to initiate a stress response. The terminal endings of these neurons, located in the median eminence of the hypothalamus, release CRH and AVP into the hypothalamic-hypophysial portal vessel system, where they travel to the anterior pituitary. The two neuropeptides act syn-ergistically on pituitary corticotrophs to activate the synthesis of pro-opiomelanocortin (POMC). This peptide, discussed in detail below, is processed to produce several peptides including adrenocorticotrophic hormone (ACTH), or corticotropin. ACTH released from corticotrophs travels via the bloodstream to act on cells in the zona fasciculata layer of the adrenal cortex, stimulating the synthesis and release of the glucocorticoids, cortisol (in humans) or corticosterone (in rodents). 

The human adrenal cortex secretes a number of steroid hormones that are involved with a wide range of metabolic processes from three discrete anatomical zones the zona fasciculata, the mna reticularis, and the zona glomerulosa. 

The zona glomerulosa also secretes 18-hydroxy-corticosterone, a precursor steroid in the aldosterone biosynthetic pathway. This steroid also has mineralocorticoid properties, but is usually present in the circulation in extremely low concentrations. Mineralocorticoids are also synthesized in the zona fasciculata DOC is the most potent, but corticosterone and cortisol also have weak mineralo-corticoid activity. All of these steroids are synthesized as products of the glucocorticoid pathway. 

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-... 

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