Case Study: Fevers

So what happens when you have a fever? Does this mean your body is unable to maintain its homeostasis, in the same way your house will get too hot if your air conditioner is broken?

In extreme cases, a fever can be a medical emergency; but fever is an adaptive physiological response of our body to certain infectious agents. Certain chemicals called pyrogens will trigger your hypothalamus to shift the set point to a higher value. This is more like you programming the thermostat in your house to a higher temperature to save energy on a hot day when you are not going to be home during the day. These pyrogens can come from microorganisms that infect you, or they can be produced by your body cells in response to an infection of some sort.

Practice Questions

1. As the level of pyrogens increases in your blood, and the set point resets higher, chemoreceptors now stimulating the hypothalamus are responding to ________ as the variable, rather than thermoreceptors responding to body temperature as the variable.
   1. temperature
   2. pyrogens
   3. heart rate
   4. blood pressure
   Show Answer

   Option b is correct. The increase in pyrogen chemicals in the blood is stimulating the receptors that reset the upper temperature limit for a febrile response. Temperature is the variable during normal body temperature regulation, but not in this scenario. The blood carries the chemical that is stimulating the febrile response, but the heart rate won’t directly stimulate this receptor. The blood carries the chemical that is stimulating the febrile response, but the blood pressure won’t directly stimulate this receptor.
2. The control center is the _________.
   1. skeletal muscle
   2. sweat glands
   3. blood vessels
   4. hypothalamus
   Show Answer

   Answer d is correct. The hypothalamus is the control center for both normal body temperature homeostasis and febrile response.The skeletal muscle, sweat glands, and blood vessels are are all effectors.
3. Because the set point has been increased, you now feel cold even though you have what would normally be a body temperature within the healthy range. This produces the “chills” you feel when you get a fever. In response, the hypothalumus will work to increase body temperature. Which response will do this?
   1. The hypothalamus will stimulate sweat glands and dilating blood vessels as effectors to cool off the body.
   2. The hypothalamus will stimulate skeletal muscles to shiver and constricting blood vessels.
   Show Answer

   Option b is correct. This would increase the body temperature. Option a would decrease the body temperature.

Although the evidence is only indirect, fever is believed to enhance the body’s immune response. The increased temperature may actually impair the replication of infecting bacteria and viruses that are adapted to survive best at your normal homeostatic body temperature range. This can give your immune cells a chance to destroy the microorganisms before they can rapidly multiply and spread in the body. There is also some indirect evidence that increased body temperature slightly modifies several metabolic reactions in ways that also allow the immune system to function more efficiently.

Practice Questions

1. Once the new higher set point is reached, the thermoreceptors stimulate the _________ as the control center.
   1. skeletal muscle
   2. sweat glands
   3. blood vessels
   4. hypothalamus
   Show Answer

   Option d is correct. The hypothalamus is the control center for both normal body temperature homeostasis and febrile response. Muscles, sweat glands, and blood vessels are effectors; they do not serve as a control center.

2. In response, the sweat glands and blood vessels (effectors) are stimulated to _________.
   1. secrete sweat for evaporation and dilate vessels for increased heat loss from blood near the surface of the skin.
   2. shiver to create heat and constrict vessels to conserve heat by keeping blood away from the surface of the skin.
   Show Answer

   Option a is correct. This will cool the body. Option b would warm the body.

Unfortunately during some infections, pyrogen levels come in “waves.” This adjusts your temperature set point up and down. When pyrogen levels dip, you get the other part of the fever experience: “the sweats” and feeling flushed. As long as the pyrogen levels continue to increase and decrease you will feel like you are swinging back and forth.

Practice Question

1. Once the pyrogen level is reduced because the infection is under control, the ________ (control center) will reset the higher set point to normal.
   1. thermoreceptors
   2. chemoreceptors
   3. hypothalamus
   Show Answer

   Option c is correct. The hypothalamus is still the control center that responds to a stimulus from some type of receptor. Thermoreceptors and chemoreceptors stimulate the control center in response to a change in the variable they monitor, in this case body temperature.

Your body will continue to swing back and forth between the body’s normal upper and lower temperature limits, but because it is now within your “normal” temperature range, you probably won’t even notice that your body is still at work, maintaining the homoeostasis of this variable.

Practice Question

1. Patients often get a fever after an operation. Which of the following would not be a reasonable cause of such a response?
   1. Tissue trauma from the operation has stimulated body cells to release pyrogens.
   2. Despite precautions, some bacteria have infected the person during the operation.
   3. The operation has damaged the thermoreceptors
   4. Post-operative medications have impacted the immune system, causing the release of pyrogens.
   Show Answer

   Option c is correct. Thermoreceptors are located throughout the body, so it is unlikely an operation would directly damage all the receptors. All other options could be a cause of post-operative fever.