Epinephrine is best described as which of the following?

• A. Neurotransmitter released by sympathetic nerves; lowers heart rate.
• B. Hormone secreted by adrenal glands. Raises rate of blood circulation, breathing rate and carbohydrate metabolism in preparation for muscle exertion.
• C. Neurotransmitter released by adrenal medulla; increases metabolism.
• D. Hormone produced by the pituitary gland; regulates cortisol.

Answer: (D)

Epinephrine acts as a circulating hormone produced by the adrenal medulla that readies the body for intense activity. Its effects include increasing heart rate and the force of heart contractions, raising blood circulation and, through various pathways, increasing respiration and carbohydrate metabolism to provide quick energy for muscle exertion. In the body, epinephrine is released into the bloodstream, not primarily as a neurotransmitter from sympathetic nerves, and it is not produced by the pituitary gland. So the best description is that epinephrine is a hormone secreted by the adrenal glands, producing the systemic changes listed.