Adrenal cortex zones

The adrenal cortex is functionally divided into three zones, the zona glomerulosa, fasciculata, and reticularis. Only the outermost zone, the zona glomerulosa, synthesizes aldosterone. The other zones are responsible for the generation of glucocorticoids and androgens. 

Cortisol synthesis requires three hydroxylases located in the fasciculata and reticularis zones of the adrenal cortex that act sequentially on the Cjy, C21, and Cjj positions. The first two reactions are rapid, while Cu hydroxylation is relatively slow. If the C, position is hydroxylated first, the action of 17a-hydroxylase is impeded and the mineralocorticoid pathway is followed (forming corti-... 

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 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-... 

Following short-term inhalation exposure to 160 ppm [620 mg/m ] methyl bromide (6 h per day on five days per week for up to six weeks), B6C3F, mice were found to be more sensitive than Fischer 344/N rats 50% of male mice died after eight exposures and 50% of female mice after six exposures, while similar mortality was observed in male rats only after 14 exposures. Neuronal necrosis and testicular degeneration were observed in both species nephrosis was observed in nearly all mice, while necrosis of the olfactory epithelium was more marked in rats. Myocardial degeneration occurred in rats and to a lesser degree in male mice. In the adrenal cortex, there was cytoplasmic vacuolation in rats and inner zone atrophy in female mice (Eustis et al., 1988). 

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 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. 

Mineralocorticoid refers to those steroids that regulate salt homeostasis (sodium conservation and potassium loss) and extracellular fluid volume.Aldosterone is the most potent naturally occurring mineralocorticoid and is synthesized exclusively in the zona glomerulosa region of the adrenal cortex. This zone uniquely contains the enzyme aldosterone synthase, an obligatory enzyme in the synthetic pathway to aldosterone. Other adrenocortical steroids that have mineralocorticoid properties with varying degrees of potency include DOC, 18-hydroxy-DOC, corticosterone,... 

Estriol is produced in very large amounts during the last trimester of pregnancy. The biosynthetic pathway requires three organs to be fully functioning fetal adrenal, fetal liver, and placenta (Figure 54-14). The fetal adrenal cortex possesses a unique zone for the production of steroids. The demand for estriol is so great that the fetal adrenal is massive... 

Physiology The adrenal cortex is divided into three distinct zones, each of... 

The glucocorticoid pathway is confined to the zona fasciculata of the adrenal cortex and it is catalyzed by the same CYP21 enzyme that is involved in the mineralocorticoid pathway in this zone along with CYPl IBl. The principal difference between the two pathways in the zona fasciculata is the initial substrate, and this explains... 

Adrenocorticotropic Hormone (ACTH) (Corticotropin) Anterior Pituitary (Corticotroph) 39 aa 2p25 Stimulates steroidogenesis in all three zones of the adrenal cortex, thereby increasing secretion of cortisol, DHEAS, and aldosterone. Stimulated by CRH and inhibited by cortisol. 

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. 

The adult adrenal cortex is divided into three zones histologically the outermost zona glomerulosa, the middle zona fasciculata, and the inner zo a reticularis. All three zones are exclusive steroid producers together, they can produce all classes of steroid hormones. Under normal conditions the major products are 11-hydroxylated C21... 

Formation of active corticosteroids in each zone of the adrenal cortex involves a series of transformations... 

Diagrammatic representation of zone-specific steroid synthesis in the adrenal cortex. All three zones can convert cholesterol into pregnenolone, but because of the presence/absence of certain enzymes, the flow of pregnenolone is preferentially directed to the synthesis of the steroid for which the particular zone is specific. It has not been determined whether the zona fasciculata produces dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) in physiologically significant amounts. 

The fetus can synthesize the steroid nucleus (B22, B23, R9, S24), and in this respect the fetal zone of the adrenal cortex in utero is very active. Its production is considerable and owing to a low activity of the enzyme 3/ -HSD (B23, C8, G2, G3, V6), is largely composed of 3 8-hydroxy-A steroids. There is evidence that 3j8-HSD is at least to some extent substrate specific (Bl, V5), and histochemical findings have shown that 3jS-HSD enzymes specific for certain substrates may be present and active in the fetal zone of the adrenal gland (Cl). The level of some of the 3/ -hydroxy-A steroids in fetal blood is higher than that of any other known steroid (cholesterol apart) in human blood at any time. Simmer and co-workers (S20) have indicated that about 75 mg of DHA are produced every 24 hours in late pregnancy and possibly even more 16a-OH-DHA (D9, M16). Certain of the steroids formed, notably DHA, are used by the placenta for estrogen production, but the role of many others remains to be elucidated. 

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. 

The fascicular and reticular zones of the adrenal cortex also produce andtx>gens — androstenedione. DHA (dehydroepi-androsterone) and DHA sulphate. These compounds probably owe their andro-... 

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. 

In the cat s adrenal cortex, Bennett found that yellow phenylhydra-zones and metallic silver both appeared predominantly in the outer portion of the zona fasciculata, the so-called spongy zone. These reactions failed to develop if the sections were previously extracted with acetone or ethyl alcohol at room temperature, indicating that the reactive compounds were readily soluble in such lipid solvents. In this same zone, the cells contained abundant small hpid droplets, as demonstrated with Sudan dyes or osmic acid. 

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