What Is Pyrexia? - Definition, Causes & Symptoms - Video & Lesson Transcript | Study.com

What Is Pyrexia? - Definition, Causes & Symptoms

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  • 0:00 Pyrexia: A Natural…
  • 0:45 How Does A Fever Work?
  • 1:49 The Body's Internal Thermostat
  • 2:45 Treatment Of Pyrexia
  • 3:35 Abnormal Symptoms Of Pyrexia
  • 4:20 Lesson Summary
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Lesson Transcript
Bethany Lieberman

Bethany is a certified OB/GYN nurse who has a master's degree in Nursing Education.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

In this lesson, you will learn about a naturally occurring response from the immune system called pyrexia, which restricts the growth of bacteria and viruses in the body. Afterward, test your knowledge with a quiz.

Pyrexia: A Natural Immune Response

Have you ever wondered how we survived before the age of medicine? With so much controversy over vaccinations and the overuse of antibiotics causing resistant strains of superbugs, what did we do before we had medicine and access to healthcare?

Fortunately, we were designed with a complex mechanism of our own immune system called 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.

How Does Fever Work?

To understand what a fever is, we first need to discuss normal temperature. For example, a goat's core temperature is 105 degrees Fahrenheit, and a human's is 98.6 degrees Fahrenheit. I bet you're wondering how the heck they got a goat to put a thermometer in its mouth. Bad news: They probably had to resort to a rectal thermometer!

The temperature varies slightly depending on where in the body it was measured. For example, a rectal thermometer measures the body's internal core temperature by inserting a thermometer into the rectum.

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).

So the temperature taken rectally (internally) will be higher and more accurate than if taken in the mouth or on the skin. Despite this, taking one's temperature rectally is far less common - it is certainly more convenient to take a temperature under the armpit or in someone's mouth as opposed to rectally at every doctor's appointment.

The Body's Internal Thermostat

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.

Treatment of Pyrexia

In most cases, fever does not need to be treated, because it is a sign that the body is working hard to defeat an infection or disease. Children usually have more fevers due to an immature immune system, and the American Academy of Pediatrics recommends easing uncomfortable symptoms as opposed to bringing a child's temperature back to a normal range. In much the same way, we don't go around medicating baby goats with fever; instead, we usually take a watch-and-see approach and let the fever run its course and fight off the bacteria or virus.

An antipyretic, such as over-the-counter ibuprofen or acetaminophen, may be given for pain or excessive crying related to a fever. Non-medical treatment for fevers include removing layers of clothing, lowering room temperature, applying a cool washcloth or soaking in a lukewarm bath.

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Additional Activities

Writing Prompts on the Definition, Causes, and Symptoms of Pyrexia

Read each scenario below and provide a brief written answer to each question. Use the given lesson as a reference.

Prompt 1

A 40-year-old woman was rushed into the emergency room in a nearby hospital. She has a continuous fever that started after returning from a one-month vacation in Hongkong. While in Hongkong, she developed knee pain from an accident, which migrated to multiple other joints. She also experienced mild nausea, decreased appetite, and chills for several weeks. Her temperature was around 107 degrees Fahrenheit. Her doctor pointed out that her rising temperature was due to her severe knee pain.

  1. Is the patient experiencing pyrexia?
  2. What could happen if her temperature rises to 107.6 degrees Fahrenheit and is left untreated?

Prompt 2

A 15-year-old boy complained about having rapid and shallow breathing and was later admitted to a medical facility. His breathing rate was about 20 breaths per minute, and his skin had a bluish-gray tint. He confessed to having traveled to Africa a couple of days ago but denied any sick contacts. His condition gradually worsened within a day of admission and he developed additional symptoms, including chest pain, shivering, vomiting, and a very high fever. To make things worse, his family, who traveled along with him, were also admitted for showing the same symptoms. Doctors found out that they have contracted a bacterial infection while in Africa.

  1. How do their bodies fight against these bacteria?
  2. Why do people shiver when having a fever?

Sample Answers

Prompt 1

  1. Yes, the patient's rise in body temperature is also referred to as pyrexia. This mechanism is developed by her immune system to fight the infection caused by her knee.
  2. Once her temperature rises above 107 degrees Fahrenheit and is left untreated, it will cause severe brain damage.

Prompt 2

  1. The hypothalamus changes the body's normal body temperature set point to hinder the growth and lower the number of bacteria.
  2. Shivering is a reaction caused by the movement of blood towards the internal core of the body. This reaction is part of the body's natural response to illness and helps in raising the temperature.

Medical Disclaimer: The information on this site is for your information only and is not a substitute for professional medical advice.

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