Pharmacology Test: Opioid Analgesia

Explanation
Miosis refers to the constriction of the pupil, and it is a well-known effect of morphine. The explanation for why significant tolerance does not develop to this action of morphine is that miosis is primarily mediated by the activation of opioid receptors in the iris sphincter muscle, which is not subject to the same degree of tolerance development as other effects of morphine. This means that even with prolonged use of morphine, the pupil-constricting effect will continue to occur consistently.

Explanation
Morphine is a potent opioid analgesic that acts on the central nervous system. It is commonly used for pain relief but also has several other effects. Vagal stimulation refers to the activation of the vagus nerve, which can cause a decrease in heart rate and blood pressure. Miosis refers to constriction of the pupil, a common side effect of morphine. Postural hypotension refers to a drop in blood pressure upon standing, which can also occur with morphine use. However, morphine is not typically used as an antiemetic, which is a medication that helps prevent or treat nausea and vomiting.

Explanation
The correct answer is "Direct cardiac depression." Morphine is known to induce a fall in blood pressure through various mechanisms, such as direct reduction of vascular tone, vasomotor centre depression, and histamine release. However, direct cardiac depression is not one of the factors involved in the morphine-induced fall in blood pressure.

Explanation
Morphine stimulates the Edinger Westphal nucleus. The Edinger Westphal nucleus is responsible for controlling the constriction of the pupil in response to light. Morphine, as an opioid, can cause pupillary constriction, also known as miosis. Therefore, the stimulation of the Edinger Westphal nucleus by morphine leads to the constriction of the pupil.

Explanation
Morphine-induced constipation involves various mechanisms, including an increase in tone and a decrease in peristalsis activity of intestinal muscles, spasm of gastrointestinal sphincters, and reduction of gastrointestinal secretions. However, antivagal action is not a mechanism involved in morphine-induced constipation.