What physiological change is associated with the release of adrenaline?

The correct choice identifies that the release of adrenaline leads to an increased heart rate. When adrenaline is released, typically in response to stress or a perceived threat, it prepares the body for a 'fight or flight' response. This hormone, produced by the adrenal glands, stimulates the heart to pump faster and with more force, resulting in an increased heart rate.

This physiological change is essential for enhancing blood flow to muscles and vital organs, enabling quicker reactions and improved physical performance during stressful situations. This response not only supports immediate physical demands but also strengthens the body's overall ability to cope with danger or emergencies.

The other options do not align with the effects of adrenaline. A decrease in heart rate would contradict the action of adrenaline, as would a decrease in blood sugar levels, since adrenaline actually promotes the release of glucose into the bloodstream to provide energy. Additionally, a reduced respiratory rate does not occur; rather, the respiratory rate typically increases to supply more oxygen for heightened physical activity. Therefore, the increase in heart rate is a hallmark physiological change associated with adrenaline release.