The mammalian diving reflex activates when a person is submerged in cold water and results in which primary cardiovascular change?

• A. Diverts blood centrally after going in cold water
• B. Increases heart rate
• C. Decreases blood pressure
• D. Causes vasodilation of peripheral vessels

Answer: (A)

The mammalian diving reflex preserves oxygen by redistributing blood toward the core. When the face is exposed to cold water, a reflex causes peripheral vessels to constrict, which reduces blood flow to the limbs and skin and pushes more blood back toward the heart and brain. This central redistribution of blood is the primary cardiovascular change, helping maintain perfusion to vital organs during submersion and apnea. It’s common for heart rate to slow (bradycardia) as part of the reflex, but the key feature described here is the shift of blood from the periphery to the central circulation. The other options don’t fit because they describe effects opposite to the core mechanism (for example, increasing heart rate or peripheral vasodilation would not support central blood diversion).