Which one of the following is synthesised in human body that dilates blood vessels and increases blood flow?
Answer & explanation
Answer: (a) Nitric oxide
Nitric oxide (NO) is made by the cells lining our blood vessels (the endothelium). It diffuses into the surrounding smooth muscle and makes it relax, which widens the vessels and lets more blood flow; its discovery as a signalling molecule won the 1998 Nobel Prize in Physiology or Medicine.
- ✓ (a) Furchgott, Ignarro and Murad showed that the 'endothelium-derived relaxing factor' that dilates blood vessels is nitric oxide; heart drugs such as nitroglycerin work by releasing NO.
- ✗ (b) Nitrous oxide (N2O) is 'laughing gas', used as an anaesthetic and a greenhouse gas; the body does not make it to control blood vessels.
- ✗ (c) Nitrogen dioxide (NO2) is a brown, toxic air pollutant from vehicle exhausts and combustion that irritates the lungs; it is not a body signal.
Remember · Nitric oxide (NO) = body's own vasodilator, made by the endothelium; 1998 Nobel (Furchgott, Ignarro, Murad). Nitroglycerin relieves angina by releasing NO. N2O = laughing gas.
📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 11 (practise this chapter)
Sources
- The Nobel Prize in Physiology or Medicine 1998: press release ↗ “He concluded that blood vessels are dilated because the endothelial cells produce an unknown signal molecule that makes vascular smooth muscle cells relax. … He performed a brilliant series of analyses and concluded in 1986, together with and independently of Robert Furchgott, that EDRF was identical to NO.”
- NCERT Class 11 · Fundamentals of Physical Geography, Chapter 11 “The primary GHGs of concern today are carbon dioxide (CO2), Chlorofluorocarbons (CFCs), methane (CH4), nitrous oxide (N2O) and ozone (O3).”
Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·