What hormone is secreted by the adrenal medulla and is known to increase heart rate and blood pressure?

The hormone that is secreted by the adrenal medulla and is known for increasing heart rate and blood pressure is adrenaline, also known as epinephrine. This hormone plays a crucial role in the body's fight-or-flight response, preparing the body for a quick reaction in stressful situations.

When released into the bloodstream, adrenaline binds to receptors in the heart, leading to an increase in heart rate and the force of heart contractions. This process elevates cardiac output and blood pressure, which are vital responses during emergencies or moments of high physical activity. Additionally, adrenaline also causes vasodilation in some blood vessels while inducing vasoconstriction in others, further influencing blood flow and pressure dynamics.

The other choices listed do not have this specific effect on heart rate and blood pressure. Insulin primarily regulates glucose metabolism, testosterone is involved in sexual development and secondary sex characteristics, and cortisol is a stress hormone that plays roles in metabolism and immune response but does not directly increase heart and blood pressure in the same immediate manner as adrenaline.