occurs as a consequence of PREGNANCY(when the
body’s need for thyroid hormones increases) or in
EUTHYROID SICK SYNDROME(when a health crisis dis-
rupts the entire endocrine matrix). A goiter may
cause uniform enlargement of the thyroid gland
(diffuse goiter) or isolated enlargement (nodular
goiter). Though typically a goiter is visible on the
front of the neck, occasionally a nodular goiter
forms on the back of a thyroid lobe, near the end,
pressuring the airway. Among the numerous
causes of goiter are
- iodine deficiency
- HYPOTHYROIDISM(underactive thyroid)
- HYPERTHYROIDISM(overactive thyroid), including
GRAVES’S DISEASE - THYROIDITIS(INFLAMMATIONof the thyroid gland)
- radiation exposure (such as from RADIATION
THERAPYto treat CANCERof the larynx, MOUTH, or
upper chest) - thyroid nodules (noncancerous growths)
- THYROID CANCER
Hypothyroidism, hyperthyroidism, and thy-
roiditis are the most common causes of diffuse
goiter. Thyroid nodules, which are fairly common,
and thyroid cancer, which is relatively uncom-
mon, are more likely to cause nodular goiter.
Iodine deficiency is rare in the United States
because most table salt is iodized. Symptoms of
goiter may include
- visible swelling on one side or both sides of the
neck - palpable lump in the neck, especially when
swallowing - difficulty swallowing or the sensation of some-
thing being stuck in the THROAT - difficulty breathing, usually with exhalation
Many people also have symptoms of hypothy-
roidism or hyperthyroidism, when either condi-
tion is the cause of the goiter. The diagnostic path
includes blood tests to measure the level of thy-
roid hormones, ULTRASOUNDof the neck, and often
a radionuclide scan or COMPUTED TOMOGRAPHY(CT)
SCAN. Treatment depends on the findings and the
extent to which symptoms interfere with func-
tions such as swallowing or BREATHING. If surgery
to remove the thyroid gland is necessary (thy-
roidectomy), the person will need to take lifelong
thyroid supplementation (thyroid HORMONE THER-
APY). Endocrinologists typically take an approach
of watchful waiting with a goiter that causes no
symptoms and does not affect thyroid function
(thyroid hormone levels are normal).
See also AUTOIMMUNE DISORDERS; LYMPHOMA; THY-
ROID NODULE.gonadotropin-releasing hormone (GnRH) A
peptide HORMONE, also called luteinizing hormone-
releasing hormone (LHRH), the HYPOTHALAMUS
produces to stimulate the anterior lobe of the PITU-
ITARY GLANDto synthesize and release LUTEINIZING
HORMONE (LH) and FOLLICLE-STIMULATING HORMONE
(FSH). LH and FSH in turn stimulate the gonads, or
sex glands, to produce their respective hormones.
In women the effect stimulates the OVARIESto pro-
duce ESTROGENS andPROGESTERONE, and in men
stimulates the TESTESin men to produce TESTOS-
TERONE. When these sex hormones reach certain
levels in the bloodstream the hypothalamus stops
secreting GnRH, and the gonadotropic cascade
stops—a negative-feedback loop. In women these
levels fluctuate according to the menstrual cycle.
Other hormones may also influence the release of
GnRH.
Doctors sometimes use a pharmaceutical prepa-
ration of GnRH, called a GnRH analog, to treat
ENDOMETRIOSIS. Because its chemical composition is
nearly identical to that of endogenous GnRH, a
GnRH analog binds with GnRH receptors to block
endogenous GnRH binding. This prevents the
release of LH and FSH, and consequently sup-
presses the menstrual cycle and OVULATION.
For further discussion of GnRH within the con-
text of the endocrine system’s structure and func-
tion please see the overview section “The
Endocrine System.”
See also ANTIDIURETIC HORMONE(ADH); GROWTH
HORMONE (GH); INHIBIN; MENSTRUATION; OXYTOCIN;
PROLACTIN; THYROID-STIMULATING HORMONE(THS).Graves’s disease An autoimmune disorder in
which the body produces antibodies that attack
the THYROID GLAND, producing symptoms of HYPER-
THYROIDISM(overactive thyroid gland). The mostGraves’s disease 129