A 61-year-old woman with hyperthyroidism is treated with propylthiouracil. The drug reduces the synthesis of thyroid hormones because it inhibits oxidation of

Correct Answer: D

Rationale: For iodide (I-) to be 'organified' (incorporated into thyroid hormone), it must be oxidized to I2, which is accomplished by a peroxidase enzyme in the thyroid follicular cell membrane. Propylthiouracil inhibits peroxidase and, therefore, halts the synthesis of thyroid hormones.

Correct Answer: B

Rationale: Catecholamines (e.g., epinephrine) use second messengers like cAMP.

Correct Answer: D

Rationale: Only hydrophilic hormones use second messengers; both types use plasma proteins.

Correct Answer: B

Rationale: The posterior pituitary connects to the hypothalamus via the infundibulum.

Correct Answer: B

Rationale: Prolactin (PRL) directly affects mammary glands, not other endocrine glands.