What function does norepinephrine serve in the body?

Norepinephrine plays a crucial role in the body's response to stress and is a key component of the sympathetic nervous system. One of its primary functions is to cause vasoconstriction, which narrows the blood vessels and increases blood pressure. This vasoconstriction is essential during the "fight or flight" response, allowing the body to divert blood flow to vital organs and muscles. Additionally, norepinephrine increases heart rate, which helps to enhance blood circulation and oxygen delivery throughout the body, preparing it for rapid action.

This dual function of increasing blood pressure and heart rate is critical for helping the body respond effectively to stressful situations or emergencies. Thus, the option stating that norepinephrine causes vasoconstriction and increases heart rate encapsulates its role in facilitating physical responses to stress.