What physiological changes occur during sympathetic activation?

During sympathetic activation, the body undergoes a series of physiological changes that prepare it for a "fight or flight" response. One significant change is the dilation of the bronchi. This dilation occurs because the sympathetic nervous system releases norepinephrine, which binds to beta-2 adrenergic receptors in the bronchial smooth muscle. Consequently, the airways widen, allowing for increased airflow into the lungs. This is beneficial in situations requiring heightened oxygen intake, such as during physical exertion or stress.

In contrast to this, the contraction of bronchi would lead to reduced airflow and is not aligned with the purpose of sympathetically driven physiological responses. The constriction of pupils also does not reflect sympathetic activation, as the pupil dilation is mediated by sympathetic stimulation to enhance vision in low-light or high-stress environments. Decreased heart rate is contrary to the sympathetic response; instead, sympathetic activation typically leads to an increase in heart rate to supply more oxygenated blood to the muscles and vital organs. All these considerations reinforce the understanding that dilation of bronchi is the correct answer concerning the physiological changes during sympathetic activation.