Which of the following lab data would be consistent with primary hypothyroidism?

Correct Answer: C

Rationale: Primary hypothyroidism (thyroid failure) shows low thyroid hormone production, reducing radioiodine uptake, with elevated TSH.

Correct Answer: B

Rationale: Suckling and dilation of the cervix are the physiologic stimuli for oxytocin secretion. Milk ejection is the result of oxytocin action, not the cause of its secretion. Prolactin secretion is also stimulated by suckling, but prolactin does not directly cause oxytocin secretion. Increased extracellular fluid (ECF) volume and hyperosmolarity are the stimuli for the secretion of the other posterior pituitary hormone, antidiuretic hormone (ADH).

Correct Answer: C

Rationale: Rapid external responses (e.g., reflexes) are primarily nervous system-driven, not hormonal.

Correct Answer: D

Rationale: Lipophilic hormones (steroids, thyroid hormone) bind intracellular receptors, not second messengers.

Correct Answer: C

Rationale: Lipophilic hormones (e.g., steroids) bind intracellular receptors to activate genes.