Fever: Study with Video Lessons, Practice Problems & Examples

Fever, defined as a body temperature above 37.8°C, is an innate immune response that helps eliminate pathogens. The hypothalamus regulates body temperature, and elevated temperatures inhibit bacterial growth while enhancing inflammatory responses through increased enzymatic activity. Pyrogens, which can be endogenous or exogenous, induce fever. Although fever can cause discomfort, it is a protective mechanism that accelerates the body's ability to fight infections, making it a crucial aspect of innate immunity.

Fever

This video we're going to begin our lesson on fever. And so fever is an innate effector action or an innate immune response, and it is characterized by an abnormally high body temperature. Body temperatures that are above 37.8 degrees Celsius are referred to as a fever. And so once again, this fever, this abnormally high body temperature above 37.8 degrees Celsius is part of the second line of defense in innate immunity. And so it is an innate effector action that is designed to help eliminate microbes. Now a region in the brain known as the hypothalamus is known as the body's temperature regulating center. And again normal body temperature is right around 37 degrees Celsius, And once again high body temperatures above 37.8 degrees Celsius are referred to as a fever. And these high body temperatures above 37.8 degrees can actually inhibit most bacteria from growing. And so that is a protective mechanism to help prevent and eliminate infections. Also these higher body temperatures above 37.8 degrees Celsius that are associated with fevers can also enhance protective functions of the body. For example, they can enhance the inflammatory response and enhance the release of inflammatory cytokines, which is all going to help eliminate the microbes even better in the presence of a fever. And so these enhanced protective functions of the body are really due to the increased rates of enzymatic reactions in the body's higher temperatures. And so higher temperatures will allow for enzymatic reactions to proceed at an even faster rate than what they otherwise usually would. Now, the term pyrogens refers specifically to fever-inducing cytokines. So these are going to be cytokines that are going to be released by cells that can induce fever. And so endogenous pyrogens are going to be made inside of the body, whereas exogenous pyrogens are made externally outside of the body. And so if we take a look at our image down below, notice on the left-hand side, we have this little cartoon, and notice doctor Klutch over here says he's feeling great. Let's study microbiome because he has a normal body temperature and he does not have an infection. And so his body temperature is 37 degrees Celsius or about 98 degrees Fahrenheit, which is normal body temperature. Now notice over here on the right-hand side doctor Klutch has gotten some kind of bacterial infection. And so doctor Klutch now has a fever. And so notice that his body temperature is elevated. And it is greater than 37 degrees Celsius, which is greater than 98 degrees Fahrenheit. And so notice that he's not feeling so good. And so although fevers, you do not feel very well with a fever, it is good to know that the fever is really just a response that your body is generating to help eliminate the microbes faster. And so over here on the right-hand side, we're showing you our map of the lesson on innate immunity. And once again here in this video we're talking about the second line of defense, specifically the innate effector actions, and we're specifically focusing on fever here in this lesson. And so this here concludes our brief introduction to fever. And we'll be able to get some practice applying these concepts as we move forward in our course. And so I'll see you all in our next video.

Lipopolysaccharide (LPS) is an endotoxin created by some gram-negative (-) bacteria that commonly causes fever in humans. Lipopolysaccharide is what type of molecule?

• A. Endogenous pyrogen.
• B. Exogenous pyrogen.
• C. Pathogenic pyrogen.
• D. External pyrogen.

Fever can have positive effects on the process of fighting an infection. Which of these answers is not a positive effect fever can have during an infection?

• A. High body temperatures inhibiting the growth of many pathogenic bacteria.
• B. High body temperatures increase the enzymatic reactions associated with the immune system.
• C. High body temperatures enhance the inflammatory response and release of inflammatory signals.
• D. High body temperatures constrict the blood vessels ensuring the infection does not spread throughout the body.

Here’s what students ask on this topic:

What is the role of the hypothalamus in regulating body temperature during a fever?

The hypothalamus acts as the body's temperature-regulating center. During a fever, pyrogens (fever-inducing cytokines) signal the hypothalamus to raise the body's set point temperature above the normal 37°C. This elevated set point leads to an increase in body temperature, which helps inhibit bacterial growth and enhances the body's immune response. The higher temperature accelerates enzymatic reactions, boosting the inflammatory response and the release of cytokines, thereby aiding in the elimination of pathogens.

How do pyrogens induce fever, and what are the differences between endogenous and exogenous pyrogens?

Pyrogens are substances that induce fever by signaling the hypothalamus to raise the body's temperature set point. Endogenous pyrogens are produced within the body, typically by immune cells in response to infection. Examples include cytokines like interleukin-1 (IL-1) and tumor necrosis factor (TNF). Exogenous pyrogens originate outside the body, such as bacterial toxins. Both types of pyrogens trigger the hypothalamus to increase body temperature, aiding in the immune response by inhibiting pathogen growth and enhancing immune functions.

Why is fever considered a beneficial response in the immune system?

Fever is beneficial because it creates an environment less favorable for bacterial growth and enhances the body's immune response. Elevated temperatures inhibit the replication of many pathogens and increase the rate of enzymatic reactions, which boosts the inflammatory response and the release of cytokines. This accelerated immune activity helps the body eliminate infections more efficiently. Although fever can cause discomfort, it is a protective mechanism that supports the body's efforts to fight off pathogens.

What are the potential risks associated with high fever?

While fever is generally a protective response, excessively high body temperatures can be dangerous. Prolonged high fever can lead to dehydration, electrolyte imbalances, and in severe cases, febrile seizures, especially in young children. Extremely high fevers (above 40°C or 104°F) can cause damage to body tissues and organs, leading to complications such as brain damage. Therefore, it is important to monitor fever and seek medical attention if it becomes excessively high or persistent.

How does fever enhance the inflammatory response?

Fever enhances the inflammatory response by increasing the rate of enzymatic reactions in the body. Higher temperatures accelerate the production and activity of inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF). These cytokines promote the recruitment of immune cells to the site of infection, increase vascular permeability, and stimulate the production of acute-phase proteins. This heightened inflammatory response helps to contain and eliminate pathogens more effectively.