Congenital hypothyroidism is thyroid hyposecretion present from birth; it was formerly called cretinism, now regarded as an insensitive term. Severe or prolonged adult hypothyroidism can cause myxedema (MIX-eh-DEE-muh). Both syndromes are described in table 17.8, and both can be treated with oral thyroid hormone.
A goiter is any pathological enlargement of the thyroid gland. Endemic goiter (fig. 17.25) is due to dietary
iodine deficiency. There is little iodine in soil or most foods, but seafood and iodized salt are good sources. Without iodine, the gland cannot synthesize TH. Without TH, the pituitary gland receives no feedback and acts as if the thyroid were understimulated. It produces extra TSH, which stimulates hypertrophy of the thyroid gland. In the earlier-described toxic goiter, by contrast, the overgrown thyroid produces functional TH.
Because of their location and small size, the parathyroids are sometimes accidentally removed in thyroid surgery. Without hormone replacement therapy, the resulting hypoparathyroidism causes a rapid decline in blood calcium levels and leads to fatal tetany within 3 or 4 days.
Saladin: Anatomy & I 17. The Endocrine System I Text I I © The McGraw-Hill
Physiology: The Unity of Companies, 2003 Form and Function, Third Edition
Hyperparathyroidism, excess PTH secretion, is usually caused by a parathyroid tumor. It causes the bones to become soft, deformed, and fragile; it raises the blood levels of calcium and phosphate ions; and it promotes the formation of renal calculi (kidney stones) composed of calcium phosphate. Chapter 7 further describes the relationship between parathyroid function, blood calcium, and bone tissue.
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