Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow?
Contents10
- ANitric oxide
- BNitrous oxide
- CNitrogen dioxide
- DNitrogen pentoxide
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Answer: (A) Nitric oxide
Correct Answer: (a) Nitric oxide.
Nitric oxide (NO) is naturally produced in the human body and acts as a vasodilator — it relaxes the walls of blood vessels, widening them to increase blood flow and lower blood pressure.
The other options:
- Nitrous oxide (N₂O) — 'laughing gas,' used in anaesthesia. NOT a vasodilator in the body.
- Nitrogen dioxide (NO₂) — a toxic air pollutant. NOT produced by the body for this purpose.
- Nitrogen pentoxide (N₅O₅) — a reactive chemical compound. Not relevant to human biology.
Fun fact: The discovery that nitric oxide is a signalling molecule in the cardiovascular system won the Nobel Prize in Medicine in 1998.
Nitric oxide is the only nitrogen compound naturally produced by human cells to regulate blood pressure and circulation.
UPSC is testing whether students can distinguish between similar-sounding nitrogen compounds and identify which one has biological function versus industrial/chemical uses.
Nitric Oxide as Vasodilator
Science And Technology Nitric oxide dilates blood vessels increases blood flow
Nitric Oxide (NO): Body's Natural Vasodilator
Nitric oxide (NO) is naturally synthesized in human body and acts as vasodilator
Relaxes smooth muscles in blood vessel walls, causing vasodilation
Discovery of NO as cardiovascular signaling molecule won Nobel Prize in Medicine 1998
Produced by endothelial cells lining blood vessels
What is Vasodilation
Vasodilation means widening of blood vessels when smooth muscles in vessel walls relax. This increases blood flow and reduces blood pressure — exactly what nitric oxide (NO) does naturally in our body.
How NO Works
Endothelial cells (inner lining of blood vessels) produce NO from amino acid L-arginine
NO diffuses into smooth muscle cells surrounding blood vessels
Activates enzyme guanylate cyclase, leading to muscle relaxation
Result: vessel diameter increases, blood flow improves, blood pressure drops
Medical Applications
Application | Mechanism | Example |
|---|---|---|
Heart disease treatment | Improves coronary blood flow | Nitroglycerin releases NO |
Erectile dysfunction | Increases penile blood flow | Sildenafil (Viagra) enhances NO pathway |
Pulmonary hypertension | Dilates lung blood vessels | Inhaled NO therapy |
Wound healing | Promotes tissue blood supply | NO donors in medical research |
Trap: Nitrous oxide (N₂O) is laughing gas used in anesthesia — NOT the vasodilator
Trap: Nitrogen dioxide (NO₂) is toxic air pollutant — NOT produced by human body
Trap: Don't confuse NO with other nitrogen compounds — only nitric oxide has this biological function
Nitrogen Oxides: Medical vs Industrial
Science And Technology Nitrous oxide Nitrogen dioxide Nitrogen pentoxide
Nitrogen Oxides: Distinguishing Medical, Industrial & Toxic Forms
Only nitric oxide (NO) acts as natural vasodilator in human body
Nitrous oxide (N₂O) is medical anesthetic gas, not a vasodilator
Nitrogen dioxide (NO₂) is toxic air pollutant from vehicle emissions
Key Nitrogen Oxides
Compound | Formula | Primary Use/Source | Biological Effect |
|---|---|---|---|
Nitric oxide | NO | Body's natural signaling molecule | Vasodilator - increases blood flow |
Nitrous oxide | N₂O | Medical anesthesia, dental procedures | Anesthetic - 'laughing gas' |
Nitrogen dioxide | NO₂ | Vehicle exhaust, industrial emissions | Toxic - respiratory irritant |
Nitrogen pentoxide | N₂O₅ | Laboratory chemical synthesis | Reactive - not biologically relevant |
Why This Matters
UPSC tests precise knowledge of chemical compounds. While all these contain nitrogen and oxygen, only NO has the specific biological role of vasodilation. The others serve completely different purposes.
Trap: All options contain nitrogen and oxygen — read carefully for exact chemical formulas
Trap: N₂O sounds medical but it's anesthetic, not vasodilator
Trap: Don't associate air pollution (NO₂) with beneficial body functions
Cardiovascular Signaling Molecules
Science And Technology
Key Signaling Molecules in Cardiovascular System
Nitric oxide (NO) - primary vasodilator, Nobel Prize discovery 1998
Endothelin - potent vasoconstrictor, opposes NO action
Prostaglandins - diverse effects on blood vessels and platelets
Major Cardiovascular Signaling Molecules
Molecule | Source | Primary Effect | Clinical Relevance |
|---|---|---|---|
Nitric oxide (NO) | Endothelial cells | Vasodilation, antiplatelet | Heart disease, hypertension treatment |
Endothelin-1 | Endothelial cells | Vasoconstriction | Pulmonary hypertension, heart failure |
Prostacyclin (PGI₂) | Endothelial cells | Vasodilation, antiplatelet | Prevents thrombosis |
Angiotensin II | Renin-angiotensin system | Vasoconstriction | Blood pressure regulation |
Adenosine | Cardiac cells | Coronary vasodilation | Cardiac stress testing |
Clinical Significance
Endothelial dysfunction (reduced NO production) is early sign of cardiovascular disease
Many heart medications work by enhancing NO pathway or blocking vasoconstrictors
Balance between vasodilators (NO, prostacyclin) and vasoconstrictors (endothelin, angiotensin II) maintains blood pressure
NO measurement in breath is used as biomarker for airway inflammation
Trap: Endothelin constricts vessels while NO dilates — opposite effects from same cell type
Trap: Don't confuse prostaglandins (various effects) with NO (primarily vasodilation)