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3 Cards in this Set
- Front
- Back
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A teenage boy is seen at the office of a dental surgeon for extraction of an impacted wisdom tooth. He is so nervous that the dentist decides to administer a sedative to calm the boy. After IV administration of the sedative (promethazine), the boy relaxes and the extraction is accomplished with no complications. However, when the boy stands up from the dental chair, he turns very pale and faints. Lying on the floor, he rapidly regains consciousness, but has a rapid heart rate of 120 bpm and a blood pressure of only 110/70 mm Hg. When he sits up, his heart rate increases to
140 bpm, his pressure drops to 80/40 mm Hg, and he complains of faintness. He is helped to a couch in the reception area, where he rests for 30 minutes. At the end of this time the boy is able to sit up without symptoms and, after an additional 15 minutes, is able to stand without difficulty. What autonomic effects might promethazine have that would explain the patient’s signs and symptoms? Why did his heart rate increase when his blood pressure dropped? |
Promethazine has potent α-adrenoceptor blocking activity in addition to its sedative, antianxiety effect. As a result, the normal autonomic response to postural change (sympathetic vasoconstriction upon standing up) was temporarily lost in the patient in this case. Marked orthostatic hypotension and syncope resulted with transient recovery upon lying down. The heart rate increased when the baroreceptors detected the drop in blood pressure because promethazine blocks α
receptors (dominant in the vessels) but not β receptors (dominant in the heart). |
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What are the 2 major subdivisions of the efferent portion of the nervous system?
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Autonomic and somatic.
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What are the 2 major subdivisions of the autonomic nervous system?
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The sympathetic (thoracolumbar) division and the
parasympathetic (craniosacral) division. |
