GasGasGas - The FRCA Primary Exam Podcast GasGasGas - Opioids Quiz, the second attempt
Oct 13, 2025
This quiz dives deep into the fascinating world of opioids. Discover how opioids work at a cellular level and explore different receptor subtypes. Learn why diamorphine is both rapid and potent, and understand the significance of pKa for drug onset. The podcast also compares the onset of alfentanil and fentanyl while discussing the critical topic of context-sensitive half-times. Key insights into morphine metabolism and the risks of respiratory depression add to the rich educational content.
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Cellular Mechanism Of Opioid Analgesia
- Opioid analgesia works via Gi-protein coupled mu receptors in CNS pain pathways.
- Activation lowers cAMP, increases K+ efflux and reduces Ca2+ influx, making neurons harder to depolarise.
Receptor Subtypes Drive Different Effects
- Different opioid receptors produce distinct clinical effects beyond analgesia.
- Mu causes respiratory depression and euphoria, kappa gives sedation and miosis, delta modulates mood, nociceptin can cause hyperalgesia or analgesia.
Why Diamorphine Acts Fast
- Diamorphine (heroin) is a lipophilic prodrug rapidly crossing membranes then converted to active 6‑monoacetylmorphine and morphine.
- High lipid solubility explains very fast CNS uptake and intense euphoria.