Which adaptation is characteristic of heat acclimation after several days of exposure?

Which adaptation is characteristic of heat acclimation after several days of exposure?

• A. Increased non-shivering thermogenesis
• B. Expanded plasma volume
• C. Decreased sweating
• D. Decreased cutaneous blood flow

Answer: (B)

Heat acclimation over several days is marked by expansion of plasma volume. This increased blood volume improves venous return and stroke volume, so the heart can maintain cardiac output during heat exposure without needing to beat as rapidly. Mechanistically, fluid and salt retention driven by hormones like aldosterone and antidiuretic hormone, along with ongoing rehydration, leads to a larger circulating volume. The practical result is better circulatory stability during heat stress: with more plasma, the body can sustain sweating and skin blood flow more effectively, delay dehydration, and keep core temperature from rising as quickly. In short, a bigger plasma volume directly enhances the body's ability to dissipate heat and maintain performance in hot conditions. Increased non-shivering thermogenesis is a cold-adaptation mechanism and isn’t a feature of heat acclimation. Decreased sweating would impair cooling, and decreased cutaneous blood flow would reduce heat loss, both of which are contrary to what heat acclimation achieves.

Heat acclimation over several days is marked by expansion of plasma volume. This increased blood volume improves venous return and stroke volume, so the heart can maintain cardiac output during heat exposure without needing to beat as rapidly. Mechanistically, fluid and salt retention driven by hormones like aldosterone and antidiuretic hormone, along with ongoing rehydration, leads to a larger circulating volume.

The practical result is better circulatory stability during heat stress: with more plasma, the body can sustain sweating and skin blood flow more effectively, delay dehydration, and keep core temperature from rising as quickly. In short, a bigger plasma volume directly enhances the body's ability to dissipate heat and maintain performance in hot conditions.

Increased non-shivering thermogenesis is a cold-adaptation mechanism and isn’t a feature of heat acclimation. Decreased sweating would impair cooling, and decreased cutaneous blood flow would reduce heat loss, both of which are contrary to what heat acclimation achieves.