Thyroid Physiology & Regulation
Q: What transporter moves iodide into thyroid follicular cells?
A: Sodium‑iodide symporter (NIS)
Q: TSH ↑, Free T4 ↓ indicates what condition?
A: Primary hypothyroidism
Q: What is the first‑line treatment for hypothyroidism?
A: Levothyroxine (T4)
Q: Which prostate zone undergoes BPH?
A: Transitional zone
Q: Name a uroselective α‑blocker.
A: Tamsulosin or Silodosin
Q: Which enzyme catalyzes iodination and coupling of MIT/DIT?
A: Thyroid peroxidase (TPO)
Q: TSH ↓, T3/T4 ↑ indicates what condition?
A: Primary hyperthyroidism
Q: Which thionamide is preferred in the first trimester of pregnancy?
A: Propylthiouracil (PTU)
Q: What IPSS score indicates moderate symptoms?
A: 8–19
Q: Which drug class shrinks prostate size?
A: 5‑alpha reductase inhibitors (finasteride, dutasteride)
Q: Which deiodinase converts T4 → T3 in peripheral tissues?
A: D1 and D2
Q: What lab pattern suggests secondary hypothyroidism?
A: Low TSH + low T4
Q: Which hyperthyroid treatment is contraindicated in pregnancy?
A: Radioactive iodine (RAI)
Q: Why does bladder hypertrophy occur in BPH?
A: Increased resistance → detrusor overwork → hypertrophy.
A patient on doxazosin reports dizziness and nearly fainting when standing. What is the cause?
A: Orthostatic hypotension from non‑selective alpha‑1 blockade.
Q: Why is T4 considered a “prohormone”?
A: It has low intrinsic activity and must be converted to T3 to exert full physiologic effects.
Q: What condition presents with hypothermia, altered mental status, and severe hypothyroid labs?
A: Myxedema coma
Q: Why do iodides worsen hyperthyroidism if used alone long‑term?
A: Escape phenomenon (Jod‑Basedow effect)
Q: Name a medication class that worsens LUTS.
A: Antihistamines (1st gen), decongestants, testosterone, diuretics.
Q: Which PDE5 inhibitor treats both ED and BPH?
A: Tadalafil (Cialis)
Q: Explain how negative feedback regulates TRH and TSH release.
A: High T3/T4 suppress TRH (hypothalamus) and TSH (pituitary), reducing further thyroid hormone production.
Q: A patient presents with fatigue, weight gain, and cold intolerance. Labs show:
TSH: 0.2 mIU/L (low)
Free T4: 0.3 ng/dL (low)
Free T3: low‑normal
Prolactin: mildly elevated
MRI: pituitary mass
What is the diagnosis, and why does this lab pattern occur?
Secondary hypothyroidism
Q: A patient develops jaundice and dark urine 3 weeks after starting PTU. What is the concern and what action is required?
A: PTU‑induced hepatotoxicity (BBW) → discontinue immediately and evaluate liver function.
Q13: A patient with BPH has an IPSS of 22, prostate volume 45 mL, and no ED. What is the best therapy?
A: Combination therapy: alpha‑blocker + 5‑ARI
Q: Which drug class is contraindicated in narrow‑angle glaucoma?
A: Anticholinergics