Q1. In humans, receptors for opioids are present in __________.
A CNS (Central Nervous System)
B Gastrointestinal tract
C Respiratory tract
D Both CNS (Central Nervous System) and gastrointestinal tract Correct
Explanation
Opioid receptors are found mainly in the central nervous system and also in the gastrointestinal tract. In the central nervous system, they are linked with pain relief, sedation, dependence and changes in breathing control. In the gastrointestinal tract, they affect intestinal movement, which is why opioids often cause constipation. The respiratory tract alone is not the standard site asked in this biology fact. Since both the nervous system and the gut contain opioid receptors, the combined choice is correct.