Which of these contracts the smooth muscles in the bronchi and gut and relaxes other muscles, such as those in the walls of the fine blood vessels?

Correct option is B

Correct Answer: (b) Histamine
Explanation:
· Histamine is a biological amine released during allergic reactions and inflammatory responses.
· It contracts smooth muscles in the bronchi and gut, leading to bronchoconstriction and intestinal spasms.
· At the same time, it relaxes smooth muscles in the walls of fine blood vessels, causing vasodilation.
Information Booster:
· Effects of histamine:
· Bronchoconstriction → difficulty in breathing (seen in asthma, allergies).
· Increased gastric secretion → stimulates stomach acid.
· Vasodilation and increased capillary permeability → redness, swelling, and fall in blood pressure.
· Antihistamines (like brompheniramine) block these effects during allergic reactions.
Additional Knowledge:
· (a) Tetradotoxin: A potent neurotoxin found in pufferfish; blocks sodium channels.
· (c) Brompheniramine: An antihistamine used to treat allergies; opposes the action of histamine.
· (d) Chlordiazepoxide: A benzodiazepine used for anxiety and sedation.