CLINICAL CASES
437
D efinitions
ACTH: Adrenocorticotropin, adrenocorticotropic hormone; a polypeptide
hormone released from the anterior pituitary into the bloodstream in
response to the binding of CRH. ACTH binds to receptors in the adrenal
cortex, causing the synthesis and release of cortisol.
CRH: Corticotropin-releasing hormone; a polypeptide hormone consisting
of 41 amino acids that is released from the hypothalamus and travels to
the adrenal cortex in a closed portal system. It binds to receptors in the
adrenal cortex causing the release of ACTH and P-lipotropin.
Cortisol: Hydrocortisone; a glucocorticoid steroid hormone synthesized by
the adrenal gland in response to binding of ACTH. Cortisol binds to
cytosolic or nuclear receptors that act as transcription factors for
glucocorticoid-responsive genes. In general, cortisol is a catabolic hor-
mone that promotes the breakdown of proteins.
Corticosteroid: A class of steroid hormones that include the glucocorti-
coids
(e.g.,
cortisol) and mineralocorticoids
(e.g.,
aldosterone).
Glucocorticoids are involved in the maintenance of normal blood glu-
cose levels, whereas mineralocorticoids are involved in mineral balance.
Hypoadrenocorticism: A failure of the adrenal cortex to produce gluco-
corticoid (and in some cases mineralocorticoid) hormones.
a-MSH: Melanocyte-stimulating hormone; a polypeptide hormone derived
from the breakdown of ACTH (the ^-terminal 13-amino acid residues).
Released from the anterior pituitary, it acts on skin cells to cause skin
darkening by the dispersion of melanin.
Proopiomelanocortin: A precursor protein synthesized in the anterior
pituitary from which are generated several polypeptide hormones. It gives
rise to ACTH, P-lipotropin, y-lipotropin, a-MSH, y-MSH, CLIP, and
P-endorphin (and potentially enkephalins and P-MSH).
D ISC U SSIO N
Cortisol is a member of the glucocorticoid steroid hormone family. It acts on
almost every organ and tissue in the body in carrying out its vital role in the
body’s response to stress. Among its crucial functions, it helps maintain blood
pressure and cardiovascular function; acts as an antiinflammatory; modulates
insulin effects on glucose utilization; and regulates metabolism of protein, car-
bohydrates, and lipids. In all of its actions, cortisol interacts with intracellu-
lar receptors to trigger their binding to specific response elements in the
promoters of target genes to influence transcription of their messenger
ribonucleic acids (mRNAs).
Cortisol is produced by the adrenal gland under the precise control of the
hypothalamus and pituitary. The hypothalamus secretes corticotropin-releasing
hormone (CRH) in response to stress. CRH acts on plasma membrane receptors
in corticotrophic cells in the anterior pituitary to stimulate their release of
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