the gastrointestinal tract also synthesize somato-
statin. Somatostatin is an inhibitory hormone that
has numerous functions related to METABOLISMand
growth. It stops the release of GROWTH HORMONE
(GH), INSULIN, GLUCAGON, and the DIGESTIVE HOR-
MONES. Somatostatin also slows the activity of the
gastrointestinal tract by reducing the release of
acids and enzymes necessary for digestion. These
actions slow the rate with which the gastrointesti-
nal tract absorbs NUTRIENTS. Somatostatin further
blocks the LIVERfrom converting glycogen to GLU-
COSE.
Endocrinologists use an injectable pharmaceuti-
cal somatostatin preparation, octreotide, to treat
ACROMEGALY, a condition that results from exces-
sive GH production. Like endogenous somato-
statin, octreotide blocks the anterior lobe of the
PITUITARY GLANDfrom secreting GH. Type 1 DIABETES,
an autoimmune disorder that destroys islet cells,
often reduces the ability of the islets of Langer-
hans to produce somatostatin. However, the
numerous other sources within the body appear
capable of maintaining an adequate supply.
For further discussion of somatostatin within
the context of the endocrine system’s structure
and function please see the overview section “The
Endocrine System.”
See also AUTOIMMUNE DISORDERS; DIGESTIVE
ENZYMES.
stress response hormonal cascade The hor-
monal responses that occur across endocrine
structures to prepare the body to manage physio-
logic stress such as a strong increase in physical
activity (for example, running). The stress
response hormonal cascade begins when the HYPO-
THALAMUSreceives input that the body is experi-
encing stress. It releases a surge of
CORTICOTROPIN-RELEASING HORMONE (CRH), which
stimulates the anterior lobe of thePITUITARY GLAND
to produce ADRENOCORTICOTROPIN HORMONE(ACTH).
Concurrently the hypothalamus releases THY-
ROTROPIN-RELEASING HORMONE (TRH), which stimu-
lates the anterior pituitary to produce
THYROID-STIMULATING HORMONE(TSH). The hypothal-
amus further stimulates, through neurotransmit-
ters, the adrenal medulla to increase the release of
EPINEPHRINEand NOREPINEPHRINE. These hormones
stimulate NERVEcell communication such as in the
muscles.
ACTH instructs the adrenal cortex of the ADRE-
NAL GLANDSto release CORTISOL, which has numer-
ous effects on cardiovascular and pulmonary
functions. Cortisol is the body’s fight-or-flight HOR-
MONEthat increases BLOODflow to critical organs,
HEART RATE, BLOOD PRESSURE, andBREATHING rate.
Cortisol also stimulates the LIVERto convert glyco-
gen to GLUCOSE, ramping up the blood supply of
this essential energy source. The increase in blood
glucose causes the ISLETS OFLANGERHANSto release
INSULIN, which prepares cells throughout the body
to receive additional glucose. TSH directs the THY-
ROID GLANDto increase secretion of the thyroid
hormones to accelerate METABOLISM, increasing cel-
lular use of the now-available glucose supplies.
This hormonal cascade remains in action for as
long as the body needs the ability to respond to
the physiologic stress it faces. For the example of
running, this might be until the running stops and
cardiovascular and pulmonary functions return to
normal levels. When the stress passes the cascades
gradually reverse until the body’s hormone levels
also return to normal. Fear, anger, and other
intense emotions also can activate the stress
response hormonal cascade. Persistent activation
of the stress response hormonal cascade eventu-
ally becomes dysfunctional, with the potential to
cause damage to blood vessels and organ systems.
See also ALDOSTERONE; HYPERTENSION; STRESS AND
STRESS MANAGEMENT.stress response hormonal cascade 159