AEMCA Practice Exam

What effects do alpha 1 receptors produce and where are they located?

1. Vasodilation; located in the CNS

2. Vasoconstriction; located on postsynaptic sites

3. Inhibition of neurotransmitter release; located on presynaptic sites

4. Muscle contraction; located in the heart

The correct answer is: Vasoconstriction; located on postsynaptic sites

Alpha 1 receptors primarily produce vasoconstriction and are located on postsynaptic sites. This is crucial for understanding their role in the sympathetic nervous system, where, upon activation, they lead to the contraction of vascular smooth muscle. This results in increased peripheral resistance and subsequently raises blood pressure, making them vital in the body's response to stress and maintaining blood flow during emergencies. By being located on postsynaptic sites, alpha 1 receptors facilitate the action of norepinephrine released from sympathetic nerve endings. When norepinephrine binds to these receptors, it triggers a series of intracellular events that culminate in the contraction of smooth muscle cells surrounding blood vessels. This physiological action is essential for various functions, including regulating blood pressure and redistributing blood flow during the fight-or-flight response. The other options describe effects or receptor locations that are associated with different types of adrenergic receptors or physiological responses. For instance, options involving vasodilation rather than vasoconstriction and those that refer to presynaptic sites or the heart do not accurately capture the primary characteristics of alpha 1 receptors. Understanding these distinctions is key in pharmacology and physiology, as it influences therapeutic strategies targeting the adrenergic system.