The cardiovascular system's response to epinephrine is determined by

• A. Blood glucose level
• B. Age of patient
• C. Receptor availability
• D. Vascular resistance

Answer: (C)

The cardiovascular response to epinephrine is determined by receptor availability. Epinephrine works by binding to adrenergic receptors on heart and blood vessels, and the exact hemodynamic effect depends on which receptors are present and responsive in those tissues. Beta-1 receptors in the heart raise heart rate and contractility, alpha-1 receptors on vessels cause vasoconstriction and increase systemic vascular resistance, and beta-2 receptors in certain beds can cause vasodilation. If a tissue has more of a particular receptor type or higher receptor sensitivity, the corresponding effect will dominate, shaping the overall response. Blood glucose level and age can influence other effects of epinephrine or affect receptor dynamics indirectly, but they do not determine the immediate cardiovascular response. Vascular resistance is part of the outcome produced by receptor actions, not the factor that dictates which response occurs.