Which statements about thyroid hormones are true?

• A. II, III
• B. III, IV
• C. I, IV
• D. I, II

Answer: (B)

Thyroid hormones set the pace of metabolism. They are produced by the thyroid gland as iodine-containing molecules (T3 and T4) and release is regulated by TSH from the pituitary through negative feedback. Once in cells, they travel to the nucleus and bind to receptors, altering gene transcription to boost metabolic processes, heat production, and overall energy use. They require iodine for synthesis, and their effects include increasing basal metabolic rate and promoting protein synthesis and mitochondrial activity.

The two statements that align with these well-established facts are the ones that describe their role in increasing metabolic rate and their iodine dependence for synthesis. Together, those reflect how thyroid hormones function and why these specific points are true. The other statements would conflict with how these hormones are produced or how they act, so they don’t fit as true descriptions.