Advanced Dental Admission Test (ADAT)

Which adrenergic receptor is primarily associated with relaxation effects on the gastrointestinal tract?

1. A1 adrenergic receptors

2. A2 adrenergic receptors

3. B1 adrenergic receptors

4. B2 adrenergic receptors

The correct answer is: A2 adrenergic receptors

The adrenergic receptor primarily associated with relaxation effects on the gastrointestinal tract is the B2 adrenergic receptor. These receptors are found in various tissues, including the smooth muscles of the gastrointestinal tract, where their activation leads to muscle relaxation and, consequently, inhibition of peristalsis and reduced motility. This process facilitates the overall relaxation of the digestive tract during times when the body may prioritize other activities, such as the "fight or flight" response, rather than digestion. In contrast, the A1 and A2 adrenergic receptors are generally more involved in vasoconstriction and other responses that tend to stimulate or regulate different physiological activities, including those associated with the sympathetic nervous system's response. The B1 adrenergic receptors mainly regulate heart rate and contractility in cardiac tissue, with minimal direct influence on gastrointestinal motility. Therefore, the B2 receptors' role is critical for mediating gastrointestinal relaxation, highlighting their importance in the autonomic regulation of digestive functions.