Questions and Answers
What is the primary mechanism by which morphine causes nausea and vomiting?
Which of the following is NOT a direct effect of morphine on the heart?
What is the effect of morphine on the release of GH and prolactin?
Which of the following is a Neuro-endocrine response to morphine?
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What is the effect of morphine on the vasomotor centre?
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What is the primary cause of postural hypotension and fainting in morphine-treated patients?
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What is the primary cause of death in morphine poisoning?
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Which of the following is NOT a CNS effect of morphine?
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What is the effect of morphine on the vasomotor centre?
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What is the effect of morphine on certain cortical areas and hippocampal cells?
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What is the effect of morphine on the temperature regulating centre?
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What is the effect of morphine on the cough centre?
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What is the characteristic of sedation caused by morphine?
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What is the effect of morphine on the respiratory centre in an otherwise healthy individual?
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What is the effect of morphine on mood and subjective effects?
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Why do patients in pain or anxiety perceive the effect of morphine as pleasurable?
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What is a primary contributor to constipation induced by morphine?
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How does morphine affect the cardiovascular system?
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Which of the following is a potential adverse effect of morphine on the respiratory system?
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What is a common neuroendocrine response to morphine administration?
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What is the primary mechanism by which morphine causes opioid-induced nausea?
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Which of the following statements regarding morphine's effect on the biliary tract is correct?
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Which of the following statements is TRUE about morphine's pharmacokinetics?
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What is the primary reason for morphine's unreliable oral absorption?
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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.
