Choose all that describe a beta-adrenergic receptor.
A. It uses a calcium second messenger system.
B. It inhibits smooth muscle of the bronchioles, enhancing airflow.
C. It uses a cAMP second messenger system.
D. It is usually inhibitory.
The Correct Answer and Explanation is :
The correct options that describe a beta-adrenergic receptor are B and C.
Explanation:
Beta-adrenergic receptors are part of the G protein-coupled receptor (GPCR) family and primarily respond to catecholamines such as epinephrine (adrenaline) and norepinephrine (noradrenaline). These receptors are classified into three main types: β1, β2, and β3, each with distinct physiological roles.
B. It inhibits smooth muscle of the bronchioles, enhancing airflow.
This statement is true for β2-adrenergic receptors, which are found in the smooth muscle lining the bronchioles of the lungs. When activated by catecholamines, these receptors induce bronchodilation, which relaxes the smooth muscle, leading to the widening of the airways and improved airflow. This is particularly important in the treatment of asthma and chronic obstructive pulmonary disease (COPD), where bronchodilators (like albuterol) target β2 receptors to relieve constricted airways.
C. It uses a cAMP second messenger system.
Beta-adrenergic receptors are primarily linked to the activation of adenylate cyclase through the Gs protein pathway, which increases intracellular levels of cyclic adenosine monophosphate (cAMP). Elevated cAMP levels result in various physiological responses, including increased heart rate (positive chronotropic effect), increased force of cardiac contraction (positive inotropic effect), and smooth muscle relaxation (as seen in bronchodilation). This second messenger system is critical in mediating the effects of beta-adrenergic stimulation on target tissues.
A. It uses a calcium second messenger system.
This statement is incorrect. Calcium second messenger systems are primarily associated with other types of receptors, like alpha-adrenergic receptors, which often lead to muscle contraction through calcium mobilization.
D. It is usually inhibitory.
This statement is also incorrect. While some responses mediated by beta-adrenergic receptors can be inhibitory, such as the inhibition of certain smooth muscle contractions, overall, the predominant effects are excitatory (such as increased heart rate and bronchodilation).
In summary, beta-adrenergic receptors primarily enhance physiological functions through the cAMP signaling pathway and are particularly important in managing conditions like asthma and heart failure.