JBL EMT Complete Practice Exam 2025

An increase in heart rate and contractility occurs due to the stimulation of alpha-1 receptors. Alpha-1 receptors are located in various tissues, including blood vessels and the heart. When these receptors are stimulated, they cause the heart to beat faster (increase in heart rate) and with more force (increase in contractility). This response is part of the body's sympathetic nervous system activation, where the fight-or-flight response is triggered to prepare the body for action.

The other options are not correct because:

- Alpha-2 receptors are more involved in inhibiting the release of norepinephrine, leading to a decrease in sympathetic activity.

- Beta-1 receptors are primarily found in the heart and are responsible for increasing heart rate and contractility when stimulated.

- Beta-2 receptors are mainly located in the lungs and blood vessels, and their stimulation leads to bronchodilation and vasodilation, not an increase in heart rate and contractility.