With respect to Ca metabolism

Correct Answer: D

Rationale: PTH inhibits PO₄ reabsorption (increases excretion) in kidneys, lowering serum PO₄ while raising Ca²⁺ dual action defines it. PTH increases Ca reabsorption, not decreases. PO₄ secretion rises, not falls. Calcitonin reduces bone resorption. PTH's PO₄ effect distinguishes it, critical for calcium-phosphate balance, unlike Ca reabsorption, secretion, or calcitonin errors.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: A

Rationale: Steroid hormones, derived from cholesterol, are lipid-soluble, enabling membrane crossing e.g., cortisol, testosterone. Peptide hormones (e.g., insulin) are water-soluble, amines (e.g., adrenaline) from tyrosine not cholesterol. The question's cutoff omits options, but 'steroid hormones' aligns with endocrine science and prior answer 'C' (likely misaligned OCR). This cholesterol origin distinguishes steroids' synthesis and action, crucial for their role in stress, reproduction, and metabolism, unlike protein-based hormones.

Correct Answer: C

Rationale: The posterior pituitary releases oxytocin (uterine contraction, milk ejection) and antidiuretic hormone (ADH, water retention), not anterior pituitary hormones like prolactin, GH, MSH, FSH, TSH, or ACTH. This neurohypophyseal role distinguishes it, key to labor and hydration, contrasting with anterior functions.

Correct Answer: D

Rationale: Thyroid hormones (T3/T4) elevate BMR by accelerating cellular metabolism, unlike insulin (glucose storage), ACTH (cortisol trigger), or glucagon (glucose release). 'D' inferred from context. This distinguishes thyroid's systemic energy role, critical for thermoregulation, contrasting with acute metabolic regulators.