American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Which receptor types are activated by norepinephrine?

1. Alpha 1 and 2 only

2. Beta 1 only

3. Alpha 1, 2, and Beta 1

4. Beta 1 and Beta 2 only

The correct answer is: Alpha 1, 2, and Beta 1

Norepinephrine is a key neurotransmitter in the sympathetic nervous system and primarily acts on adrenergic receptors. The correct choice involves both alpha and beta receptors, specifically Alpha 1, Alpha 2, and Beta 1. Alpha 1 receptors are located on vascular smooth muscle and their activation leads to vasoconstriction, increasing blood pressure. Alpha 2 receptors are inhibitory and primarily found on presynaptic terminals; their activation can diminish further release of norepinephrine, serving a modulating role in neurotransmission. Beta 1 receptors are found primarily in the heart, and activation of these receptors increases heart rate and contractility, ultimately elevating cardiac output. Norepinephrine does not activate only one type of receptor; it engages multiple receptors which work together to produce the physiological responses associated with the "fight or flight" response. This broad action facilitates the body’s ability to respond to stressors. In contrast, the other options, which limit the action to fewer receptor types, fail to encompass the full range of norepinephrine's effects in the body. Thus, recognizing the different types of receptors it interacts with is crucial for understanding its role in physiological processes.