Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow ?
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Answer: A. The body makes nitric oxide (NO) in the lining of blood vessels. It relaxes the smooth muscle of vessel walls, widening the vessels (vasodilation) and increasing blood flow. Drugs like nitroglycerine work by releasing nitric oxide.
Watch for: Nitric oxide and nitrous oxide sound alike; nitrous oxide is laughing gas.
Why the other options are wrong
- B. Wrong because nitrous oxide (laughing gas) is an anaesthetic, not made by the body to widen vessels.
- C. Wrong because nitrogen dioxide is a toxic air pollutant.
- D. Wrong because nitrogen pentoxide is not produced in the human body.
Source to check: NIH National Library of Medicine, 'Nitric oxide' (MedlinePlus / StatPearls); Nobel Prize in Physiology or Medicine 1998 press release
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.