STRESS RESPONSE HORMONAL CASCADEand stimulates
the anterior lobe of the PITUITARY GLANDto produce
ADRENOCORTICOTROPIC HORMONE (ACTH). ACTH in
turn stimulates the ADRENAL GLANDSto release COR-
TISOL, a steroid hormone that has numerous
actions in the body. The level of cortisol in the
bloodstream is one of the endocrine signals that
determines the release of CRH. The hypothalamus
also releases CRH in a rhythmic pattern that coin-
cides with the body’s circadian cycle of sleep and
wake. CRH levels peak just before dawn and
trough just before dusk, establishing higher ACTH
and cortisol levels during the waking hours.
For further discussion of CRH within the con-
text of the endocrine system’s structure and func-
tion, please see the overview section “The
Endocrine System.”
See also GONADOTROPIN-RELEASING HORMONE
(GNRH); GROWTH HORMONE–RELEASING HORMONE
(GHRH); THYROTROPIN-RELEASING HORMONE(TRH).
cortisol A HORMONEthe adrenal cortex of the
ADRENAL GLANDSproduces. Chemically cortisol is a
glucocorticosteroid, a type of steroid (cholesterol-
based structure) that influences carbohydrate and
fat METABOLISM(GLUCOSEbalance) in the body. Cor-
tisol is the main player in the STRESS RESPONSE HOR-
MONAL CASCADE, essential for activating other
hormones and chemical processes required for
many vital functions within the body. All cells in
the body have receptors for cortisol. The body
requires a minimum level of cortisol in the blood-
stream, as well as increased amounts of cortisol to
respond to stress by raising BLOOD PRESSURE, HEART
RATE, BREATHING, and metabolic rate. Cortisol also
counters the body’s IMMUNE RESPONSE, helping to
subdue areas of INFLAMMATIONafter they develop.
Cortisol levels fluctuate in a rhythmic pattern
over the course of 24 hours, being highest during
waking hours when the body is most active and
lowest a few hours after falling asleep. To main-
tain this pattern the HYPOTHALAMUSinitiates a cas-
cade of hormonal activity by releasing
CORTICOTROPIN-RELEASING HORMONE (CRH) in syn-
chronization with the body’s circadian rhythm
(cycle of wake and sleep). CRH stimulates the
anterior lobe of the PITUITARY GLAND to release
ADRENOCORTICOTROPIN HORMONE (ACTH). ACTH in
turn causes the adrenal cortex to produce and
release cortisol. When the BLOODlevel of cortisol is
adequate, the hypothalamus ceases release of
CRH, the pituitary gland ends release of ACTH,
and the adrenal cortex stops cortisol production.
When the cortisol level in the blood drops or
physiologic sensors (such as barosensors that
detect changes in blood pressure) indicate a need
to respond to stress the hypothalamus again
boosts CRH output.
Cortisol production increases in response to
physiologic stress such as intense physical exer-
cise, as well as to emotional stress such as fear or
anger. Research suggests that persistently elevated
cortisol levels result in long-term damage to the
cardiovascular system, notably contributing to
HYPERTENSION (high blood pressure) and ARTE-
RIOSCLEROSIS(stiffening of the arteries). Chronically
insufficient levels of cortisol in the blood result in
ADDISON’S DISEASE; chronically excessive levels of
cortisol in the blood result in Cushing’s syndrome.
People who take long-term CORTICOSTEROID MEDICA-
TIONS to treat chronic inflammatory conditions
may develop acquired Cushing’s syndrome, also
called hyperadrenocorticism. Pharmaceutical
preparations of cortisol commonly used as anti-
inflammatory medications are cortisone and
hydrocortisone.
For further discussion of cortisol within the
context of the endocrine system’s structure and
function please see the overview section “The
Endocrine System.”
See also ALDOSTERONE; DOPAMINE; EPINEPHRINE;
NOREPINEPHRINE; STRESS AND STRESS MANAGEMENT;
WORKPLACE STRESS.Cushing’s syndrome A constellation of symp-
toms that occur as a consequence of high levels of
CORTISOLin the bloodstream. Cushing’s syndrome
may result from long-term CORTICOSTEROID MEDICA-
TIONS(exogenous Cushing’s syndrome) or from
excessive cortisol production within the body
(endogenous Cushing’s syndrome). Untreated
Cushing’s syndrome affects many vital functions
including BLOOD PRESSUREand HEART RATE, and can
be fatal.Exogenous Cushing’s Syndrome
Exogenous Cushing’s syndrome is the more com-
mon form of this condition and typically occurs in116 The Endocrine System