Encyclopedia of Health and Medicine

growth hormone–releasing hormone (GHRH) 131
permanent damage to the eyes and vision. No
known preventive measures exist for Graves’s disease.
See also IMMUNE RESPONSE; LYMPHOCYTE; THYROIDI-
TIS; THYROID STORM; VISION HEALTH.
growth hormone (GH) A peptide HORMONE the
PITUITARY GLAND produces in response to secretion
of GROWTH HORMONE–RELEASING HORMONE (GHRH) by
the HYPOTHALAMUS. GH affects growth directly by
initiating an increase in cell division and indirectly
by stimulating the production of insulinlike
growth factors (IGFs), proteins that affect cell
METABOLISM and other functions. GH levels are
highest in childhood, then taper off in early adulthood
to maintain a stable level. GH remains essential
in adulthood to maintain appropriate cell
metabolism, notably in BRAIN, MUSCLE, and fat cells.
GROWTH HORMONE DEFICIENCY in childhood results in
stunted growth, and in adulthood can result in
diminished cognitive function, decreased muscle
mass, and increased body fat. Some researchers
believe the decline in GH in adulthood contributes
to the aging process, though the mechanisms
through which this occurs remain unknown.
Excessive GH secretion, such as may occur with a
pituitary ADENOMA, results in ACROMEGALY.
For further discussion of growth hormone
within the context of the endocrine system’s
structure and function please see the overview
section “The Endocrine System.”
See also ADRENOCORTICOTROPIN HORMONE (SCTH);
ANABOLIC STEROIDS AND STEROID PRECURSORS; ANTIDI-
URETIC HORMONE (ADH); FOLLICLE-STIMULATING HOR-
MONE (FSH); HUMAN GROWTH HORMONE (HGH)
SUPPLEMENT; LUTEINIZING HORMONE (LH); OXYTOCIN;
PROLACTIN; THYROID-STIMULATING HORMONE (TSH).
growth hormone deficiency An endocrine disorder
in which the anterior lobe of the PITUITARY
GLAND produces an inadequate amount of GROWTH
HORMONE (GH). GH is fundamental for proper
growth and development in childhood and
remains essential for appropriate metabolic function
in adulthood. In childhood GH binds to
receptors in BONE cells that increases the rate at
which they divide, causing bone growth that
results in increased height. In adulthood GH deficiency
can affect cognitive functions and memory,
body mass and fat distribution, and numerous
aspects of cell METABOLISM.
It is important to distinguish between abnormal
growth and a child who is simply short in stature.
The average rate of growth for children is about
two inches a year. Many factors influence a child’s
ultimate height. Indications in addition to short
stature that a child may have GH deficiency
include accumulations of body fat in the abdomen
and the face (giving a rounded, chubby appearance),
delayed eruption of TEETH, and in an older
child, delayed PUBERTY. The diagnostic path
includes
• BLOOD tests to measure thyroid hormones
(HYPOTHYROIDISM can cause slowed growth) and
insulinlike growth factors (IGFs)
• measuring height and weight over a period of
time to detect growth patterns
• X-rays and sometimes COMPUTED TOMOGRAPHY
(CT) SCAN to evaluate bone structure
• a GROWTH HORMONE–RELEASING HORMONE (GHRH)
challenge test to measure the ability of the
pituitary gland to respond to stimulation by
GHRH
Treatment for confirmed GH deficiency in children
is injections of recombinant human growth
hormone (hGH), a genetically engineered substance
that has the precise configuration of
endogenous GH, continued until the child reaches
appropriate growth. Some people develop antibodies
to the recombinant hGH, decreasing its
effectiveness. When the pituitary gland is congenitally
absent (a birth defect) or permanently damaged,
long-term hGH therapy may be necessary.
Whether treatment continues into adulthood
depends on symptoms and the cause of the deficiency.
Doctors do not agree on the definition or
the need for treatment of adult growth hormone
deficiency that does not begin in childhood.
See also ACROMEGALY; ADRENAL INSUFFICIENCY;
HUMAN GROWTH HORMONE (HGH) SUPPLEMENT; POLY-
GLANDULAR DEFICIENCY SYNDROME; TURNER’S SYNDROME.
growth hormone–releasing hormone (GHRH)
A peptide HORMONE the HYPOTHALAMUS produces to
stimulate the PITUITARY GLAND to synthesize and