Activation of sympathetic nerves that innervate lung tissue results in which of the following effects?

• A. Increased mucus secretion
• B. Decreased respiratory rate
• C. Bronchodilation
• D. Bronchoconstriction

Answer: (C)

Verified step by step guidance

1. Understand the role of the sympathetic nervous system: The sympathetic nervous system is part of the autonomic nervous system and is responsible for the 'fight or flight' response. It generally prepares the body for action by increasing heart rate, dilating airways, and redirecting blood flow to essential organs.
2. Focus on the lungs: Sympathetic activation in the lungs primarily affects the smooth muscle in the bronchioles. The neurotransmitter released by sympathetic nerves is norepinephrine, which binds to beta-2 adrenergic receptors on the smooth muscle cells.
3. Explain bronchodilation: When norepinephrine binds to beta-2 adrenergic receptors, it causes relaxation of the smooth muscle in the bronchioles. This relaxation leads to bronchodilation, which increases the diameter of the airways and facilitates airflow, making breathing easier during a 'fight or flight' response.
4. Rule out other options: Increased mucus secretion is typically associated with parasympathetic activation, not sympathetic activation. Decreased respiratory rate is also not a sympathetic effect; instead, the respiratory rate often increases during sympathetic activation. Bronchoconstriction is the opposite of bronchodilation and occurs during parasympathetic activation or allergic reactions.
5. Conclude the correct effect: Based on the physiological mechanisms, activation of sympathetic nerves that innervate lung tissue results in bronchodilation, which is the correct answer.