Lecture 9: Opioid Analgesics Flashcards
What is nociception
Sensory processing and transmission of noxious stimuli
What are the affective components of pain (2)
Sensation and tissue damage
Opioids are effective at addressing both ___and ___
Pain transmission and affective components (sensation and tissue damage)
Opioids are the most effective analgesics available for ___
Tx of systemic acute pain
What is the pain transmission pathway
- Spinal nerves
- Spinal cord in dorsal horn
- Release substance P and glutamate
- Spinal cord—>brain
- Descending pathway
What 3 ways do opioids block pain
Inhibit perception, transduction and modulate the spinal pathway
Where are Mu receptors found
Brain and in the spinal cord in dorsal horn
What does activation of mu receptors result in
Sedation, supraspinal and spinal analgesia, miosis, respiratory depression, euphoria, inhibition of ACh and dopamine release, decrease GI motility
Where are kappa receptors found
Cerebral cortex, spinal cord and other brain regions
What is the result of activating kappa receptors
Spinal and supraspinal analgesia, mild sedation, inhibition of vasopressin, miosis
Less respiratory depression than mu
Where are delta receptors located
Limbic system, cerebral cortex and spinal cord
What is the result of activating delta receptors
Spinal and supraspinal analgesia, inhibition of dopamine release and cardiovascular depression
What is the mechanism of action of opioids
- Act on Gi proteins
- Decrease cAMP
- Close VG Ca2+ channels
- Decrease NT release- ACh, glutamate, substance P, NE
- Open presynaptic K+ channels (mu) causing hyperpolarization
- Promote release of endogenous opioids that further inhibit pain transmission
What are the two overall effects of opioids
- Inhibition of pain transmission
- Simulation of descending inhibitory neurons
The primary use for opioids is ___
Analgesia
What are the endogenous opioids
Endorphins, enkephalins, dynorphins
Release of endorphins causes ___
Euphoria
Release of enkephalins causes ___
Decreases our sensation and reaction to pain
Drugs that stimulate __ receptors produce profound analgesia
U receptors
What is the mechanism in which opioids provide analgesia
They decrease the transmission of pain in the spinal cord and the sensation of pain in the cerebral cortex, increase release of encephalin from PAG further reducing pain transmission
Opioid receptors undergo ___ and ___ which may lead to decrease effect overtime/ tolerance
Desensitization and downregulation
What effects do opioids have on the CNS
At low doses: sedation
At high doses: excitement
Horses and cats: excitement
Dogs: sedation
Opioids may cause ___ in dogs
Dysphoria
Opioids may cause ___ and ___ in cats
Dysphoria and increased motor activity
What are the effects of opioids on the pupils
Miosis in most species
Mydriasis in cats and horses
What effects do mu receptor agonists have on respiratory system
They are respiratory depressants, increase arterial CO2 and decrease arterial O2 and pH
Result in panting in dogs and resetting hypothalamic temperature set point
What are the effects of opioids on the cardiovascular system
Bradycardia
Hypotension- vasodilation due to histamine release
What opioid is most likely to cause vasodilation from histamine release
Morphine
____ and ____ in cats from histamine may become dangerous
Pruritis and excoriation
What are the GI effects from opioids
- Stimulate CRTZ- vomiting
- Aspiration from vomiting
- Decrease GI-constipation and decrease gastric empty
- Anti-diarrhea
What receptors does morphine act on
Full mu receptor agonist
High doses stimulate kappa receptors