Which hormone acts as a vasoconstrictor and is produced by the adrenal medulla?

Norepinephrine is correct because it serves as a vasoconstrictor and is produced by the adrenal medulla. This hormone plays a crucial role in the body’s response to stress and is involved in the regulation of blood pressure by constricting blood vessels, which leads to an increase in blood pressure. Norepinephrine is part of the body's fight-or-flight response, where it helps redirect blood flow to essential organs and muscles during times of stress.

The other hormones listed do not primarily function as vasoconstrictors or are not produced by the adrenal medulla. Adrenaline (also known as epinephrine) is primarily associated with increasing heart rate and dilating air passages rather than direct vasoconstriction. While both norepinephrine and epinephrine are catecholamines, norepinephrine has a more pronounced effect on vasoconstriction. Serotonin, on the other hand, is primarily involved in mood regulation and does not have significant effects on blood vessel constriction in the way norepinephrine does.