Which statement best describes norepinephrine?

Which statement best describes norepinephrine?

• A. It decreases heart rate.
• B. It causes vasodilation.
• C. It is produced by the adrenal cortex.
• D. It increases heart rate and causes vasoconstriction.

Answer: (D)

Norepinephrine acts as a sympathetic transmitter that increases heart activity and constricts blood vessels. It binds to alpha-1 receptors on vascular smooth muscle, causing vasoconstriction and higher peripheral resistance, which raises blood pressure. It also stimulates beta-1 receptors in the heart to boost heart rate and contractility. This combination explains why the correct statement describes both an increase in heart rate and vasoconstriction. It does not cause vasodilation, and it is not produced by the adrenal cortex (cortex hormones are produced there; norepinephrine is released by sympathetic nerves and the adrenal medulla).

Norepinephrine acts as a sympathetic transmitter that increases heart activity and constricts blood vessels. It binds to alpha-1 receptors on vascular smooth muscle, causing vasoconstriction and higher peripheral resistance, which raises blood pressure. It also stimulates beta-1 receptors in the heart to boost heart rate and contractility. This combination explains why the correct statement describes both an increase in heart rate and vasoconstriction. It does not cause vasodilation, and it is not produced by the adrenal cortex (cortex hormones are produced there; norepinephrine is released by sympathetic nerves and the adrenal medulla).