🧷 Authentic Classroom Explanation by IAS Monk

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📌 The Question:

Which one of the following is synthesised in the human body that dilates blood vessels and increases blood flow?

(a) Nitric oxide
(b) Nitrous oxide
(c) Nitrogen dioxide
(d) Nitrogen pentoxide

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✅ Answer: (a) Nitric oxide

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🧑‍🏫 Classroom Explanation:

Nitric oxide (NO) is a biologically active gaseous molecule naturally produced in the human body, especially by the endothelial cells lining blood vessels.

🔹 Nitric oxide acts as a vasodilator, meaning it relaxes smooth muscles in blood vessel walls.
🔹 This relaxation causes widening of blood vessels, leading to:

• Increased blood flow
• Reduced blood pressure

Other options are incorrect:

• Nitrous oxide (N₂O) → Anaesthetic gas (“laughing gas”), not a physiological vasodilator
• Nitrogen dioxide (NO₂) → Toxic air pollutant
• Nitrogen pentoxide (N₂O₅) → Industrial chemical, not produced in the body

👉 Hence, option (a) is correct.

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🔍 Curiosity Raiser:

🫀 Did you know?
The molecule responsible for heart health is actually a gas — invisible, short-lived, yet life-saving.

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📚 Enrichment Notes (UPSC Edge):

• Nitric oxide is synthesized from L-arginine by the enzyme Nitric Oxide Synthase (NOS)
• Plays a role in:
  • Cardiovascular health
  • Neurotransmission
  • Immune response
• Discovery of NO as a signalling molecule won the 1998 Nobel Prize in Physiology or Medicine
• Drugs like nitroglycerin work by increasing nitric oxide availability

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🧘 IAS Monk Whisper:

🩺 Sometimes the smallest molecules carry the greatest power.
Health flows where vessels learn to relax.