The _________ produces the hormone melatonin.

Correct Answer: B

Rationale: The pineal gland secretes melatonin to regulate sleep.

Correct Answer: A

Rationale: Thyroid hormone, an amine, acts on its target tissues by a steroid hormone mechanism, inducing the synthesis of new proteins. The action of antidiuretic hormone (ADH) on the collecting duct (V2 receptors) is mediated by cyclic adenosine monophosphate (cAMP), although the other action of ADH (vascular smooth muscle, V1 receptors) is mediated by inositol 1,4,5-triphosphate (IP3). Parathyroid hormone (PTH), β 1 agonists, and glucagon all act through cAMP mechanisms of action.

Correct Answer: B

Rationale: Neurosecretory neurons in the hypothalamus release hormones (e.g., ADH, oxytocin) into the blood.

Correct Answer: D

Rationale: Amines (e.g., epinephrine, thyroxine) are tyrosine-derived and secreted by thyroid and adrenal medulla.

Correct Answer: B

Rationale: Cyclic AMP is the primary second messenger for hydrophilic hormones (e.g., glucagon).