Which of the following is an effect of norepinephrine binding to beta-2 adrenergic receptors?

• A. Stimulation of digestive gland secretion
• B. Bronchodilation in the lungs
• C. Increased heart rate
• D. Constriction of blood vessels in the skin

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the role of norepinephrine in the autonomic nervous system. Norepinephrine is a neurotransmitter and hormone that primarily acts on adrenergic receptors, which are divided into alpha and beta subtypes. Beta-2 adrenergic receptors are specifically involved in smooth muscle relaxation in certain tissues.
2. Step 2: Learn the physiological effects of beta-2 adrenergic receptor activation. When norepinephrine binds to beta-2 adrenergic receptors, it triggers a signaling cascade that leads to the relaxation of smooth muscles, particularly in the airways and blood vessels.
3. Step 3: Focus on the lungs. Beta-2 adrenergic receptor activation in the lungs causes bronchodilation, which is the widening of the airways. This effect helps improve airflow and is critical during the 'fight or flight' response.
4. Step 4: Eliminate incorrect options. Stimulation of digestive gland secretion is not associated with beta-2 adrenergic receptors; it is more related to parasympathetic activity. Increased heart rate is primarily mediated by beta-1 adrenergic receptors, not beta-2. Constriction of blood vessels in the skin is mediated by alpha adrenergic receptors, not beta-2.
5. Step 5: Conclude that the correct effect of norepinephrine binding to beta-2 adrenergic receptors is bronchodilation in the lungs, as this aligns with the receptor's role in smooth muscle relaxation in the airways.