Thyroid and Parathyroid Hormones Clinical Chemistry Review 110
HORMONE REGULATES COMMENTS
Thyroid
Thyroxine (T 4 )
Triiodothyronine (T 3 )
Calcitonin
Parathyroid
Parathyroid hormone (PTH)
Principle thyroid hormone. 50 × more concentrated than
T 3. Contains 4 atoms of I. Regulated by TSH. Most bound
to thyroxine-binding globulin (TBG). ↑in hyperthy-
roidism, ↓in hypothyroidism
Most formed from deiodination of T 4 by tissues. Contains
3 atoms of I.4×–5× more potent than T 4. Regulated
by TSH. ↑in hyperthyroidism, ↓in hypothyroidism
Important in diagnosis of thyroid cancer
Primary hyperthyroidism = ↑PTH, ↑Ca2+, ↓phosphate
Hypoparathyroidism = ↓PTH, ↓Ca2+, ↑phosphate
Metabolism, growth, & development
Metabolism, growth, & development
Inhibition of Ca2+resorption
Regulation of Ca2+& phosphate
