EPO

Correct Answer: D

Rationale: Erythropoietin (EPO) production from kidneys is inhibited by theophylline (adenosine antagonist), reducing RBC stimulation in hypoxia. It increases RBC via progenitor division, but takes days, not 24 hours. Inactivation is hepatic/renal, not spleen-specific. Theophylline's suppression distinguishes it, critical for EPO regulation, unlike action, inactivation, or timing claims.

Correct Answer: D

Rationale: Prostaglandins (e.g., PGE2) increase renin secretion, enhancing RAAS in low perfusion/stress. Renin converts angiotensinogen to angiotensin I, but angiotensin II triggers aldosterone indirect. Conversion occurs in blood (renin), not lungs (ACE to angiotensin II). High Na at macula densa suppresses renin. Prostaglandin stimulation distinguishes it, critical for RAAS activation, unlike indirect, site, or Na 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.