Human body temperature is controlled within very narrow limits - AQA - GCSE Biology - Question 10 - 2021 - Paper 1

The temperature near the brain decreased because the blood, which is being cooled by the ingestion of ice-cold water, loses heat as it returns from the stomach and mouth. As a result, cooler blood flows to the brain, lowering its temperature.

The thermoregulatory centre sends information to the sweat glands through nerve impulses. These impulses carry electrical signals that instruct the sweat glands to either increase or decrease sweating in response to temperature changes.

As the rate of sweating increases, more sweat evaporates from the skin. This evaporation process helps to cool the body, ensuring that less heat is retained and allowing the individual's body temperature to remain stable despite external temperature fluctuations.

The skin appears red due to the dilation of blood vessels in the skin. This process increases blood flow to the skin's surface, helping to release excess heat generated during exercise.