Fever (pyrexia)

Pyrexia

Pyrexia is a rise in the body's core temperature, otherwise known as a fever. It is a mechanism developed by the immune system to reduce the severity of illness by preventing bacteria and viruses from multiplying. This activation of the immune system has worked for centuries before medicine was invented. Most individuals view a fever as something that is bad or harmful, but it is a sign that our body is working in our favor to fight disease.

An axillary temperature measures the temperature under the armpit, which tells the temperature on the surface of the skin. An oral temperature is taken by placing a thermometer under the tongue, which measures the temperature in the oral cavity (mouth).

The body's temperature actually fluctuates throughout the day and in response to activity and sleep patterns. The usual culprits - those not related to bodily injury or disease - are exercise, eating, medication, menstrual cycle, hot weather and humidity.

We have an internal thermostat called the hypothalamus, which is a small gland located in the brain. This gland functions as a part of the nervous system, sending signals out to the mechanisms that heat and cool the body. The hypothalamus responds to the presence of biochemical communicators called pyrogens, which are released into the bloodstream from injured body tissues or from the presence of disease-causing microorganisms.

The pyrogens cause the hypothalamus to increase the body temperature. This works to lower the amount of bacteria and virus in the body, because the high temperature makes it difficult for them to multiply and replicate. The heating process acts by shunting blood away from the extremities to the internal core of the body. This induces shivering that also raises temperature.