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4.6.11 How an infectious disease can interfere with the body’s negative feedback mechanisms for the thermoregulation

Homeostasis is the maintenance of the body’s internal environment. This is carefully controlled by a series of systems, which aim to keep conditions at a stable controlled level.

Body Tempereature

Body temperature is carefully regulated to maintain a steady 37.5˚C, which is the optimum temperature for human enzymes. Sensors (thermoreceptors) in the hypothalamus continually monitor blood temperature and activate warming / cooling processes to keep  the temperature as stable as possible.

Tuberculosis bacterium (Mycobacterium tuberculosis) causes fever.

How does fever work?

All white blood cells communicate with each other and the rest of the immune system using a class of hormones called cytokines. The cytokines have hundreds of different roles and many more are yet to be discovered. One class of cytokine is the hormone interleukin,  which causes fever.

 

Fever can be induced by many factors. The general class of hormones that lead to fever are called pyrogens (interleukin is a natural pyrogen). However, bacterial toxins, viral proteins and substances produced by necrotic tissue may also trigger fever.

 

Pyrogens travel in the blood to the hypothalamus in the brain. They bind to receptors there and trigger a complex set of reactions that lead to the production of PGE2 hormone, which

 

elevates the thermoregulatory set point, i.e. it re-sets the body’s natural thermostat to a higher temperature.

 

The hypothalamus now thinks body temperature is too low and triggers a system of responses which aim to generate heat (thermogenesis) and raise body temperature. These mechanisms include; shivering, increased muscle tone, vasoconstriction and the production of thyroxine hormone (which makes respiration less efficient, therefore producing more heat).