Rigor, or rigors, are caused by the presence of pyrogens in the blood, which essentially reset the body's internal thermostat to a higher temperature.
Here's a more detailed breakdown:
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Pyrogens and the Thermostat: Think of your body as having a thermostat that regulates your core temperature. Pyrogens are chemicals that act on the hypothalamus (the temperature control center in the brain) to increase the body's "set point."
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Source of Pyrogens: These pyrogens are often produced by your own immune system in response to various triggers. The most common trigger is an infection, such as a bacterial or viral infection. They can also be released from damaged tissues during trauma or surgery.
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The Body's Response: When the body's thermostat is set higher, it initiates mechanisms to reach that new, higher temperature. These mechanisms include:
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Shivering: This generates heat through muscle contractions. Shivering is the hallmark of a rigor.
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Vasoconstriction: Blood vessels near the skin's surface constrict, reducing heat loss to the environment. This is why someone experiencing rigors often feels cold and has pale skin.
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Increased Metabolism: The body increases its metabolic rate to generate more heat.
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In summary, rigors are a physical manifestation of the body attempting to raise its core temperature in response to pyrogens circulating in the bloodstream, most often due to an infection.
