Morphine's Effects on CTZ and Edinger Westphal Nucleus
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Questions and Answers

What is the primary mechanism by which morphine causes nausea and vomiting?

  • Direct depression of the vomiting centre
  • Activation of the vagal centre
  • Stimulation of the CTZ to vestibular and other impulses (correct)
  • Release of histamine in the gut
  • Which of the following is NOT a direct effect of morphine on the heart?

  • No direct effect (correct)
  • Vasodilatation
  • Increase in heart rate
  • Decrease in blood pressure
  • What is the effect of morphine on the release of GH and prolactin?

  • Decreased release
  • Variable response
  • Increased release (correct)
  • No effect
  • Which of the following is a Neuro-endocrine response to morphine?

    <p>Decreased release of FSH and LH</p> Signup and view all the answers

    What is the effect of morphine on the vasomotor centre?

    <p>Depression</p> Signup and view all the answers

    What is the primary cause of postural hypotension and fainting in morphine-treated patients?

    <p>Vasodilatation and impairment of vascular reflexes</p> Signup and view all the answers

    What is the primary cause of death in morphine poisoning?

    <p>Respiratory failure</p> Signup and view all the answers

    Which of the following is NOT a CNS effect of morphine?

    <p>Stimulation of the vagal centre</p> Signup and view all the answers

    What is the effect of morphine on the vasomotor centre?

    <p>It is depressed at higher doses</p> Signup and view all the answers

    What is the effect of morphine on certain cortical areas and hippocampal cells?

    <p>Stimulation</p> Signup and view all the answers

    What is the effect of morphine on the temperature regulating centre?

    <p>It is depressed</p> Signup and view all the answers

    What is the effect of morphine on the cough centre?

    <p>It is depressed</p> Signup and view all the answers

    What is the characteristic of sedation caused by morphine?

    <p>Drowsiness without motor incoordination</p> Signup and view all the answers

    What is the effect of morphine on the respiratory centre in an otherwise healthy individual?

    <p>No cognizable respiratory depression</p> Signup and view all the answers

    What is the effect of morphine on mood and subjective effects?

    <p>It has a calming effect</p> Signup and view all the answers

    Why do patients in pain or anxiety perceive the effect of morphine as pleasurable?

    <p>Because it relieves their pain and anxiety</p> Signup and view all the answers

    What is a primary contributor to constipation induced by morphine?

    <p>Increased tone and segmentation in the intestines</p> Signup and view all the answers

    How does morphine affect the cardiovascular system?

    <p>Decreases peripheral resistance, leading to increased cardiac work.</p> Signup and view all the answers

    Which of the following is a potential adverse effect of morphine on the respiratory system?

    <p>Respiratory depression</p> Signup and view all the answers

    What is a common neuroendocrine response to morphine administration?

    <p>Increased cortisol levels</p> Signup and view all the answers

    What is the primary mechanism by which morphine causes opioid-induced nausea?

    <p>Stimulation of the chemoreceptor trigger zone (CTZ) in the medulla</p> Signup and view all the answers

    Which of the following statements regarding morphine's effect on the biliary tract is correct?

    <p>Morphine causes spasm of the sphincter of Oddi, leading to increased intrabiliary pressure.</p> Signup and view all the answers

    Which of the following statements is TRUE about morphine's pharmacokinetics?

    <p>Morphine is primarily metabolized in the liver by glucuronide conjugation.</p> Signup and view all the answers

    What is the primary reason for morphine's unreliable oral absorption?

    <p>Morphine undergoes significant first-pass metabolism.</p> Signup and view all the answers

    Study Notes

    Morphine Pharmacology

    Central Nervous System Effects

    • Nausea and Vomiting: Triggered by stimulation of the Chemoreceptor Trigger Zone (CTZ). Symptoms worsen with movement, especially in a full stomach.
    • Miosis: Stimulation of Edinger-Westphal nucleus from central action, not from direct topical application of morphine to the eye.
    • Cardiac Effects: Morphine stimulates the vagal center, leading to bradycardia.
    • Cortical Stimulation: Higher doses can cause muscular rigidity, immobility, and potential convulsions due to inhibition of GABA release.
    • Mood Effects: Promotes calming sensations; perceived as euphoric by patients in pain or addicts, while normal individuals may find it unpleasant.
    • Respiratory Depression: Dose-dependent decrease in respiratory rate and tidal volume, particularly harmful in patients with preexisting conditions.
    • Cough Centre: More sensitive to morphine than the respiratory center, leading to depression.
    • Temperature Regulation: Depresses the temperature regulating centre causing potential hypothermia.

    Neuro-Endocrine Actions

    • Hormonal Influence: Reduces hypothalamic control over the pituitary; leads to decreased levels of ACTH, FSH, and LH, yet an increase in GH and prolactin.
    • Sex Hormones: Clinical impacts are insignificant, except for heavy users who may experience reproductive issues.
    • Anti-diuretic Hormone: Increases ADH release, reducing urine volume.
    • Metabolic Effects: Can lead to mild hyperglycemia due to central sympathetic stimulation.

    Cardiovascular Effects

    • Vasodilation: Caused by histamine release, vasomotor center depression, and direct blood vessel action.
    • Blood Redistribution: Shifts blood from the pulmonary to systemic circulation; therapeutic doses have minimal effect on blood pressure in normovolaemic patients.
    • Postural Hypotension: May occur due to impaired vascular reflexes.

    Gastrointestinal Effects

    • Constipation: Resulting from various actions: decreased propulsive movements, increased segmentation, and sphincter spasms.
    • Inability to Tolerate Defecation: Central action decreases attention to the defecation reflex, causing chronic constipation.

    Actions on Smooth Muscles

    • Biliary Tract: Spasm of the sphincter of Oddi may lead to increased intrabiliary pressure and biliary colic.
    • Urinary Bladder: Increased tone in detrusor and sphincter causes difficulties in urination.
    • Bronchoconstriction: Histamine release can cause bronchoconstriction, posing risks for asthmatics.

    Pharmacokinetics

    • Absorption: Oral bioavailability is low (1/6 to 1/4) due to first-pass metabolism; reliable parenteral administration is preferred.
    • Plasma Protein Binding: Approximately 30% binds to plasma proteins, leading to a slow brain entry.
    • Placental Transfer: Morphine crosses the placenta, potentially affecting the fetus more than the mother.
    • Liver Metabolism: Primarily metabolized in the liver through glucuronide conjugation.
    • Half-Life: Average plasma half-life is 2–3 hours, with the effect lasting 4–6 hours; almost complete elimination occurs within 24 hours.

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    Description

    This quiz explores the effects of morphine on the chemoreceptor trigger zone (CTZ) and the Edinger Westphal nucleus of the third nerve, including symptoms and reactions.

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