Heat exhaustion is primarily characterized by increased body temperatures alongside hypothalamic responses. During heat exhaustion, the body struggles to regulate its temperature due to excessive heat exposure, leading to elevated core temperatures. This occurs as the hypothalamus, which helps maintain homeostasis, attempts to cool the body through mechanisms such as sweating and increased blood flow to the skin.
While severe dehydration can occur during heat exhaustion and might contribute to symptoms, it is not the defining characteristic. Decreased body temperature would indicate a different condition, such as heat stroke or hypothermia, rather than heat exhaustion. Increased heart rate is indeed a response to heat stress; however, it is more a symptom or a compensatory mechanism rather than a defining characteristic of heat exhaustion. The focus on the hypothalamic responses and temperature regulation highlights the body's effort to cope with overheating, making this the most accurate choice as a primary characteristic.