Which physiological system mediates compensatory changes such as increased heart rate and vasoconstriction?

• A. Sympathetic Nervous System
• B. Parasympathetic Nervous System
• C. Central Nervous System
• D. Somatic Nervous System

Answer: (A)

The sympathetic branch of the autonomic nervous system drives compensatory changes such as increasing heart rate and constricting blood vessels. It acts on the heart through beta-1 receptors to raise heart rate and contractility, and on vascular smooth muscle through alpha-1 receptors to cause vasoconstriction, which raises systemic vascular resistance and helps maintain blood pressure during stress or blood loss. Catecholamines from the adrenal medulla amplify these effects. The parasympathetic system would slow heart rate and doesn’t drive vascular constriction; the central nervous system coordinates these responses but does not directly produce them, and the somatic system handles voluntary control of skeletal muscles rather than autonomic cardiovascular adjustments.