Question

The primary action of Nitric oxide (NO) in the gastrointestinal tract is:

• A. Vasodilatation
• B. Vasoconstriction
• C. Gastrointestinal smooth muscle relaxation
• D. Gastrointestinal slow smooth muscle contraction

Hint:

NO is the chief NANC inhibitory transmitter of the gut wall.

Answer 1

The Correct Option is C

Nitric oxide in the digestive tract is best understood as the brake of the enteric nervous system. It is the main transmitter of the inhibitory NANC neurons, the nerves that tell gut muscle to let go rather than to squeeze.

Mechanistically, NO crosses into the smooth muscle cell and switches on soluble guanylyl cyclase. The resulting rise in cyclic GMP pulls calcium out of the cytosol, and with less calcium the contractile machinery cannot engage, so the muscle relaxes.

This relaxing action underlies several everyday gut functions: the stomach relaxing to accept a meal, the segment of bowel ahead of a bolus opening up so the bolus can advance, and sphincters like the lower oesophageal and internal anal sphincters loosening at the right moment.

The trap in the options is vasodilatation. NO certainly dilates vessels, but the stem specifically asks for its leading role inside the GI tract, which is muscle relaxation. Vasoconstriction and slow contraction describe the reverse of NO action, so both are wrong.

\[\boxed{\text{Gastrointestinal smooth muscle relaxation}}\]