Answer: C — Posterior communicating and posterior cerebral

Question

Correct Answer: C — Posterior communicating and posterior cerebral arteries

Reasoning

• Posterior communicating artery (anterior hypothalamus)
• Posterior cerebral artery (posterior hypothalamus)
• Small branches from the anterior cerebral and anterior communicating arteries also contribute to the anterior hypothalamus, but the dominant supply relevant to this question (and combined with thalamus/subthalamus) is from the posterior communicating + posterior cerebral system.

Why the other options are wrong

Key Takeaway for FCPS

Answer: A — Inhibits Na⁺/K⁺ ATPase, increasing intracellular calcium and myocardial contractility

Question

Correct Answer: A (98% of users agreed — and they are correct)

Full Mechanism — Step by Step

Digoxin
  ↓
Inhibits Na⁺/K⁺-ATPase pump on cardiac myocytes
  ↓
Na⁺ cannot be pumped OUT of the cell
  → Intracellular Na⁺ ↑
  ↓
Na⁺/Ca²⁺ exchanger (NCX) normally uses the Na⁺ gradient
to move Ca²⁺ OUT of the cell
  → With high intracellular Na⁺, NCX works less efficiently
  → Less Ca²⁺ is expelled
  ↓
Intracellular Ca²⁺ ↑
  ↓
More Ca²⁺ available for actin-myosin cross-bridge cycling
  ↓
↑ Myocardial contractility (positive inotropy)

Why the Other Options Are Wrong

Additional Points Relevant to FCPS Anesthesia

Key Takeaway

Answer: C — Obstructive Jaundice

Question

Correct Answer: C — Obstructive Jaundice (76% agreed — correct)

Pathophysiology — Step by Step

Bile duct obstruction (e.g., biliary atresia, choledochal cyst, gallstone)
  ↓
Bile CANNOT flow into the intestine
  ↓
Two consequences:

1. Conjugated bilirubin backs up into blood
   → Excreted by kidneys into urine
   → Dark/tea-colored urine (bilirubinuria)

2. No bile reaches intestine
   → No urobilinogen/stercobilin formed
   → Stool loses its normal brown color
   → Clay/pale/acholic stools

Classic Triad of Obstructive Jaundice (Cholestasis)

Why Other Options Are Wrong

Differentiating Types of Jaundice — Quick Summary

Anesthesia Relevance (FCPS)

• Obstructive jaundice → coagulopathy (vitamin K malabsorption → ↓ clotting factors II, VII, IX, X)
• Hepatorenal syndrome risk perioperatively
• Hepatopulmonary syndrome possible
• Pre-op: give vitamin K, check PT/INR, ensure adequate hydration
• These patients have increased risk of renal failure post-surgery (especially after biliary surgery)

Answer: C — 3600 ml/min

Question

Key Formula

• V_A = Alveolar ventilation (ml/min)
• V_T = Tidal Volume = 450 ml
• V_D = Anatomical Dead Space = 150 ml
• RR = Respiratory Rate = 12/min

Calculation

Why Not the Other Options?

Bonus: Minute Ventilation vs Alveolar Ventilation

FCPS Anesthesia Relevance

• Dead space ventilation is wasted ventilation — it does not participate in gas exchange
• Anatomical dead space ≈ 2 ml/kg (or ~150 ml in a 70 kg adult) — conducting airways
• Physiological dead space = anatomical + alveolar dead space (relevant in ARDS, PE)
• Rapid shallow breathing → ↑ dead space fraction → ↓ effective alveolar ventilation even if minute ventilation appears adequate

Answer: D — Tyrosine

Question

Correct Answer: D — Tyrosine (83% agreed — correct)

Biosynthetic Pathway from Tyrosine

TYROSINE (aromatic amino acid)
  │
  ├──► CATECHOLAMINE pathway:
  │         Tyrosine
  │            ↓ (Tyrosine hydroxylase — rate-limiting step)
  │         L-DOPA
  │            ↓ (DOPA decarboxylase)
  │         DOPAMINE
  │            ↓ (Dopamine β-hydroxylase)
  │         NOREPINEPHRINE
  │            ↓ (PNMT — in adrenal medulla)
  │         EPINEPHRINE
  │
  └──► THYROID HORMONE pathway:
            Tyrosine (in thyroglobulin)
               ↓ (iodination)
            MIT (monoiodotyrosine)
            DIT (diiodotyrosine)
               ↓ (coupling)
            T3 (Triiodothyronine) — DIT + MIT
            T4 (Thyroxine) — DIT + DIT

Why Other Options Are Wrong

Complete List of Tyrosine-Derived Products

Memory Aid

"Tyrosine = Thyroid + catecholamines + melanin" One amino acid → THREE major systems

FCPS Anesthesia Relevance

• Dopamine is used as a vasopressor/inotrope in ICU/anesthesia
• Norepinephrine is the first-line vasopressor in septic shock
• Epinephrine is used in anaphylaxis, cardiac arrest, and as a local anesthetic adjunct
• Phaeochromocytoma = excess catecholamine synthesis from tyrosine → perioperative crisis risk
• Tyrosine hydroxylase inhibition by metyrosine → used pre-op in phaeochromocytoma (Ref: Lippincott's Illustrated Reviews: Biochemistry)