How is body temperature regulated during fever?

During a fever, body temperature is regulated by the hypothalamus, which raises the body's set point temperature.

The hypothalamus, a small region in the brain, is responsible for maintaining the body's internal balance, or homeostasis, which includes body temperature. When the immune system detects a foreign substance such as bacteria or viruses, it releases chemicals called pyrogens. These pyrogens signal the hypothalamus to increase the body's set point temperature, leading to a fever.

The process begins with the immune system's detection of an invader. The immune cells produce and release pyrogens into the bloodstream. These pyrogens then travel to the brain and interact with the hypothalamus. The hypothalamus responds by producing prostaglandins, which are substances that can reset the body's thermostat to a higher temperature. This is why you feel hot and may start shivering during a fever - your body is trying to reach this new set point.

Once the new set point is reached, the body works to maintain this higher temperature until the immune system signals that the infection has been dealt with. This is done through various mechanisms such as shivering to generate heat, vasoconstriction to reduce heat loss through the skin, and increased metabolic rate to produce more heat.

The fever breaks when the immune system has dealt with the infection and stops producing pyrogens. The hypothalamus then stops producing prostaglandins, and the body's set point temperature returns to normal. The body cools down through mechanisms such as sweating and vasodilation, where blood vessels near the skin surface expand to allow more heat to escape.

In summary, the regulation of body temperature during a fever is a complex process involving the immune system and the hypothalamus. It is a part of the body's defence mechanism against infection, helping to create an environment that is less favourable for the growth and reproduction of pathogens.