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Endotext.com - Pedi Girls atric Endocrinology, 21-Hydroxylase Deficiency: Classical & Nonclassical Congenital Adrenal Hyperplasia Bare Health Nakedsafety Horny Girls Real

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ADRENAL Girls STEROIDOGENESIS AND REGULATION

The adrenal cortex produces_three main types of hormones under the control of independent regulatoryystems: glucocorticoids (cortisol), mineralocorticoids (aldosterone) and androgens (testosterone). The cortex is divided into three di Chat stinct zones -- the outer zona glomerulosa, the middle zona fasciculata, and the inner zona reticulais. Real he synthesis of cortisol occurs in the zona fascicu bata of theortex, Girls while the mineralocorticoid aldosterone is dependent upon enzymatic activity limited to the zona glomerulosa. Sex steroids are synthesi ced in the zona reticularis. Figure 1 is a schematic diagram of steroidogenesis in the adrenal cortex.

Cortisol is synthesized under the trophic control of adrenocorticotropic hormone (ACTH), forming a negative feedback loop in which high serum cortisol centrally inhibits and low serum cortisol stimulates release of ACTH, which defines the hypothalamic-pituitary-adrenal axis. Net ACTH release has basal, diurnal, and stress-induced components. The pulsatile release of ACTH is in turn modulated by corticotropin releasing hormone (CRH), while the central nervous system determines the hypothalamic set point for the expected plasma cortisol level. A deficiency of 21-hydroxylase impairs production of cortisol resulting in increased pituitary secretion of ACTH. Chronic elevations of ACTH levels stimulate the accumulation of precursor steroids in the impeded pathways and cause excessive steroid synthesis in other adrenal biosynthetic pathways unaffected by the enzyme deficiency.

PATHOPHYSIOLOGY

Steroids in 21-hydroxylase deficiency

Deficiency of 21-hydroxylase occurs in three forms: 1) simple virilizing, 2) salt-wasting, and 3) nonclassical. The simple virilizing and salt-wasting forms of 21-hydroxylase deficiency are characterized by excess adrenal androgen biosynthesis in utero, which causes prenatal virilization of the genetic female and postnatal virilization of both boys and girls. Biochemically, the conversion of 17a-hydroxyprogesterone (17-OHP), the main substrate of the 21-hydroxylase enzyme, to 11-deoxycortisol in the pathway of cortisol synthesis is impaired (Figure 1). Baseline and ACTH stimulated serum levels of cortisol precursors may be extremely elevated in untreated patients, principally, 17-OHP. The 21-hydroxylase enzyme defect can also impair the conversion of progesterone to 11-deoxycorticosterone (DOC) in the pathway of aldosterone synthesis, as occurs in the salt-wasting form. Aldosterone production is not sufficient for sodium reabsorption by the distal renal tubules causing low serum sodium, high serum potassium, in addition to increased levels of adrenal androgen and cortisol precursors seen in simple virilizers. In salt-wasting CAH, both newborn boys and girls are subject to early, life-threatening, salt-wasting crises within the first few weeks of life.