Which of the following physiological responses is increased when beta 1 receptors are stimulated?

When beta 1 receptors are stimulated, one of the primary physiological responses is an increase in heart rate. Beta 1 receptors are primarily located in the heart, where their stimulation leads to an increase in the rate at which the heart beats, known as chronotropy. This is a crucial response, especially during stress or physical activity, as it helps ensure that more blood is pumped to tissues that require increased oxygen and nutrients.

In contrast, other options like respiratory rate, vascular resistance, and bronchial secretions are more closely associated with different receptor types or physiological mechanisms. For instance, an increase in respiratory rate is typically influenced by other factors like carbon dioxide levels or directly by stimulation of different receptors found in the respiratory centers of the brain. Likewise, beta 2 receptors, rather than beta 1 receptors, are more responsive for changes related to vascular resistance and bronchial secretions. Therefore, the increase in heart rate is the direct and significant outcome of beta 1 receptor stimulation.