ABNORMAL
THYROID FUNCTION
Inadequate
secretion of thyroid hormone during fetal and neona-tal development results in
stunted physical and mental growth (cretinism)
because of general depression of metabolic activity. In adults, hypothyroidism
manifests as lethargy, slow mentation, and generalized slowing of body
functions.
Oversecretion
of thyroid hormones (hyperthyroidism) is man-ifested by a greatly increased
metabolic rate. Many of the other characteristics of hyperthyroidism result
from the increased re-sponse to circulating catecholamines (epinephrine and
norepi-nephrine). Hypothyroidism and hyperthyroidism are discussed in detail in
the following sections.
Oversecretion
of thyroid hormones is usually associated with an enlarged thyroid gland (goiter). Goiter also commonly occurs
with iodine deficiency. In this latter condition, lack of iodine re-sults in
low levels of circulating thyroid hormones, which causes increased release of
TSH; the elevated TSH causes overproduc-tion of thyroglobulin and hypertrophy
of the thyroid gland. The term euthyroid
refers to thyroid hormone production that is within normal limits.
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