750
chapter32
Endocrine Metabolism III: Adrenal Glands
TABLE 32-1
Secretion of Hormones by the Human Adrenal Glands
Hormone
Approximate Basal
(Unstimulated) Concentration
Major Site of Synthesis
in Blood*(ng/dL)
Approximate Percent
due to Adrenal
Contribution
Cortisol
Cortex (zona fasciculata)
14,000
1 0 0
Corticosterone
Cortex (zona fasciculata)
500
1 0 0
Aldosterone
Cortex (zona glomerulosa)
6
1 0 0
11-Deoxycorticosterone (DOC)
Cortex (zona glomerulosa)
6
95-100
Dehydroepiandrosterone (DHEA)
Cortex (zona reticularis)
500
85
DHEA sulfate (DHEAS)
Cortex (zona reticularis)
2 0 0 , 0 0 0
1 0 0
A4-Androstenedione
Cortex (zona reticularis)
135
30
Dopamine (DA)
Medulla
5
50
Norepinephrine (NE)
Medulla
19
2 0
Epinephrine (E)
Medulla
2
1 0 0
Total concentration (includes protein-bound fraction).
originate mainly from the zona fasciculata. The sodium-
retaining action of DOC is normally obscured by the pro-
nounced effect of aldosterone; however, in certain disease
states (e.g., CYP17 deficiency), the levels of DOC can re-
sult in hypokalemia and hypertension in the absence of
aldosterone.
Synthesis of Corticosteroids (See Chapter 30)
Formation of active corticosteroids in each zone of
the adrenal cortex involves a series of transformations
of
the
cholesterol
molecule
(steroidogenesis).
The
enzymes for steroidogenesis are distributed in mito-
chondria
and
endoplasmic
reticulum
(Figure
32-2).
Conversion of cholesterol to pregnenolone, the initial
step, is regulated by ACTH and angiotensin II (see
below). Pregnenolone in the zona glomerulosa is con-
verted to aldosterone by transformations that involve
formation of DOC (Figure 32-1). In the zona fasci-
culate pregnenolone is directed mainly at formation of
cortisol and involves 17a-hydroxylation (Figures 30-2
and 32-1).
In
the zona reticularis,
pregnenolone is
FIGURE 32-1
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 déhydroépiandrostérone (DHEA) and dehydroepiandrosterone
sulphate (DHEAS) in physiologically significant amounts.
