What occurs in the human body when environmental temperature increases?

When environmental temperature increases, perspiration begins to cool the body. This physiological response is part of the body's thermoregulation system designed to maintain a stable internal temperature despite external heat. When the body's temperature rises, sweat glands become more active, producing sweat that evaporates from the skin surface, leading to cooling. This process helps to prevent overheating and maintain homeostasis.

The other choices do not accurately represent the body's immediate response to increased environmental temperatures. For instance, a decrease in heart rate or muscle relaxation would not be immediate responses to heat; rather, the body typically responds by increasing heart rate to promote blood circulation to the skin for heat dissipation. Additionally, muscle relaxation to conserve energy does not directly relate to the mechanism of cooling the body. Furthermore, the production of more glucose is linked to energy needs, not directly to temperature regulation.