Question:hard
The \(\mu\) (Mu) opioid receptor is responsible for the following effects except
The \(\mu\) (Mu) opioid receptor is responsible for the following effects except
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Mu receptor activation gives miosis, bradycardia, and hypothermia; airway smooth muscle is not relaxed by opioids, and morphine can even trigger bronchospasm through histamine release.
Updated On: Jul 8, 2026
- Miosis
- Bradycardia
- Hypothermia
- Bronchodilation
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: List the well known opioid side effects one by one.
When a mu receptor agonist like morphine is given, the pupils get small, this is miosis. The heart rate drops, this is bradycardia. The core temperature falls a little, this is hypothermia. These three are taught together as classic mu effects across pharmacology texts.
Step 2: Ask what opioids do to the airway instead.
Rather than opening the airway, opioids are more often linked to the opposite problem. Morphine can release histamine from mast cells, and histamine narrows the bronchi. In an asthmatic or histamine sensitive patient this can bring on wheeze, not relief of it.
Step 3: Weigh this against the option list.
Three of the four options, miosis, bradycardia, and hypothermia, fit cleanly with textbook mu receptor pharmacology. The fourth, bronchodilation, does not fit at all, and the real risk with opioids runs the other way.
Step 4: Conclude.
The effect that mu receptors are not responsible for is bronchodilation.
\[ \boxed{\text{Bronchodilation}} \]
When a mu receptor agonist like morphine is given, the pupils get small, this is miosis. The heart rate drops, this is bradycardia. The core temperature falls a little, this is hypothermia. These three are taught together as classic mu effects across pharmacology texts.
Step 2: Ask what opioids do to the airway instead.
Rather than opening the airway, opioids are more often linked to the opposite problem. Morphine can release histamine from mast cells, and histamine narrows the bronchi. In an asthmatic or histamine sensitive patient this can bring on wheeze, not relief of it.
Step 3: Weigh this against the option list.
Three of the four options, miosis, bradycardia, and hypothermia, fit cleanly with textbook mu receptor pharmacology. The fourth, bronchodilation, does not fit at all, and the real risk with opioids runs the other way.
Step 4: Conclude.
The effect that mu receptors are not responsible for is bronchodilation.
\[ \boxed{\text{Bronchodilation}} \]
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