What compensatory mechanism does the body use to maintain normal blood pressure in the early phase of hypovolemic shock?

• A. Decreased heart rate
• B. Vasoconstriction of arterioles
• C. Increased production of RBCs from bone marrow
• D. Shift fluid from the interstitial to cellular spaces

Answer: (B)

In the early phase of hypovolemic shock the body relies on the baroreceptor reflex to preserve arterial pressure. Signals that blood pressure has fallen trigger the sympathetic nervous system to constrict small arteries and arterioles throughout the body, increasing systemic vascular resistance. This rise in resistance helps keep mean arterial pressure from dropping despite the reduced blood volume. Venoconstriction also helps push blood back toward the heart, supporting preload and cardiac output. This rapid vasoconstrictive response is the most effective way to maintain normal blood pressure early on. Longer-term adaptations, like producing more red blood cells, take time and won’t prevent the immediate BP drop. Shifting fluid from interstitial to cellular spaces wouldn’t increase intravascular volume and wouldn’t help stabilize blood pressure in the moment.