Certified Registered Nurse Anesthetist (CRNA) Practice Exam

Which receptor is specifically stimulated by phenylephrine?

1. Beta 1

2. Beta 2

3. Alpha 1

4. Alpha 2

The correct answer is: Alpha 1

Phenylephrine specifically stimulates alpha-1 adrenergic receptors. When phenylephrine binds to these receptors, it leads to vasoconstriction, which can elevate blood pressure and reduce nasal congestion. This effect is particularly beneficial in clinical scenarios where a rapid increase in vascular tone is needed, such as in cases of hypotension. Alpha-1 receptors are primarily located on vascular smooth muscle, and their stimulation leads to smooth muscle contraction and resultant vasoconstriction. This mechanism underpins the therapeutic uses of phenylephrine in managing conditions like hypotension during anesthesia and in decongestants. In contrast, stimulation of beta-1 receptors primarily impacts the heart and can result in increased heart rate and contractility, while beta-2 receptors mediate relaxation of smooth muscle in the bronchial passages and vascular beds. Alpha-2 receptors have a different role, mainly being inhibitory and primarily found in the central nervous system, where they modulate neurotransmitter release. Therefore, the specificity of phenylephrine for alpha-1 receptors supports its clinical applications in anesthesia and acute care management.