Biology of Disease

7.9 Disorders of the Adrenal Cortex

Adrenal glands each weigh about 5 g and are found on the upper surfaces
of the kidneys. They consist of an outer cortex and an inner medulla. The
cortex consists of three layers: the zona glomerulosa, zona fasciculata and
zona reticularis (Figure 7.27). The adrenal cortex is essential for life since it
produces three groups of steroid hormones. The glucocorticoids, such as
cortisol, and adrenal androgens, for example testosterone, are produced
by the zona reticularis and zona fasciculata and mineralocorticoids, such
as aldosterone, from the zona glomerulosa. Adrenal cortex cells have many
low density lipoprotein receptors on their surfaces enabling them to take up
precursor cholesterol rapidly from the plasma.

Cortisol (Figure 7.28 (A)) is released in response to adrenocorticotrophic
hormone (ACTH) from the anterior pituitary that, in turn, is controlled by
the release of corticotrophin releasing factor (CRF) from the hypothalamus.
Cortisol exerts a negative feedback effect on the anterior pituitary and
hypothalamus (Figure 7.28 (B)). The secretion of cortisol shows a diurnal
variation: highest in the morning, lowest at night. Cortisol stimulates an
increase in protein catabolism, hepatic glycogenolysis and gluconeogenesis
and a redistribution of adipose tissue but suppresses inflammation. About
90% of blood cortisol is bound to a cortisol binding globulin called transcortin
whilst the remaining 10% is free.

The major mineralocorticoid, aldosterone (Figure 7.29 (A)), is released in
response to hypotension, Na+ depletion or hyperkalemia (Chapter 8). A group
of cells in the kidneys called juxtaglomerular cells detect a fall in blood pressure
and secrete renin which circulates in the blood and catalyzes the conversion
of the plasma protein angiotensinogen to angiotensin I. A converting enzyme
in the lungs converts angiotensin I to angiotensin II that stimulates the release
of aldosterone from the adrenal cortex and ADH from the posterior pituitary
(Figure 7.29 (B)). Aldosterone stimulates the retention of Na+ in exchange
for K+ and H+ in the kidney tubules increasing the osmolality of the ECF and
the retention of water raising the blood pressure or the ECF volume back to

DISORDERS OF THE ADRENAL CORTEX

CZhhVg6]bZY!BVjgZZc9Vlhdc!8]g^hHb^i]:YLddY &-(

Medulla

Capsule

Zona glomerulosa

Zona fasciculata

Zona reticularis

Figure 7.27 The histological structure of the adrenal cortex.

Courtesy of Dr A.L. Bell, University of New England, College of

Osteopathic Medicine, USA.

Figure 7.28 (A) Structure of cortisol and (B) the

regulation of its secretion.

C = O

CH 2 OH

CH 3

HO CH^3 OH

O

A)

Hypothalamus

CRF

Anterior

pituitary

ACTH

Adrenal

cortex

Cortisol

B)