What is an expected action of epinephrine on the human body?

Epinephrine, also known as adrenaline, is a hormone and neurotransmitter that plays a critical role in the body's fight-or-flight response. One of its primary effects is to increase cardiac contractility, meaning it enhances the heart's ability to pump more blood with each beat. This results in an increase in the stroke volume, which, combined with an increase in heart rate, elevates cardiac output.

This action is particularly beneficial in emergency situations, such as anaphylaxis or severe asthma attacks, where there is a need for rapid and effective circulation to deliver oxygen and nutrients to tissues. Increased cardiac contractility also helps support blood pressure in cases where it might be dangerously low, although the primary mechanism for increasing blood pressure in epinephrine's role comes from its vasoconstrictive properties on certain blood vessels, leading to increased systemic vascular resistance.

The other options do not reflect the expected actions of epinephrine. Rather than causing blood vessels to dilate, epinephrine predominantly causes vasoconstriction in many vascular beds, which helps increase blood pressure. It does not cause bronchospasm; in fact, its action on the beta-2 adrenergic receptors leads to bronchodilation, making airways wider and easier to breathe.