Which set comprises the three main adrenergic receptor types in the sympathetic nervous system?

• A. Alpha One; Beta One; Beta Two
• B. Alpha One; Alpha Two; Beta One
• C. Alpha One; Beta One; Gamma
• D. Alpha Two; Beta Two; Delta

Answer: (A)

The idea being tested is which receptor subtypes are primarily responsible for mediating the classic sympathetic (adrenergic) responses. Alpha-1 receptors on vascular smooth muscle cause vasoconstriction, helping raise blood pressure and redirect blood flow. Beta-1 receptors, mainly in the heart, increase heart rate, contractility, and conduction, boosting cardiac output. Beta-2 receptors, found in bronchial and some vascular smooth muscle, produce bronchodilation and vasodilation in skeletal muscle beds, supporting airflow and muscle perfusion during stress. These three receptor types together account for the broad, systemic effects of sympathetic activation, which is why they are regarded as the main adrenergic receptors.

There are other adrenergic receptors, like Alpha-2 and Beta-3, but they have more specialized roles and are less central to the typical rapid sympathetic responses. Some options include receptors that aren’t adrenergic (such as gamma or delta), which aren’t part of the adrenergic family.