Week 118 - Pyrexial Illness Flashcards
There are four patterns of fever, what are they?
1) Intermittent Fever- One in which the temperature returns to normal at least every 24 hours.
2) Remittent Fever- The temperature does not return to normal but fluctuates by a couple of degrees in either direction.
3) Sustained Fever - Remains above normal with only minimal variation.
4) Relapsing Fever - Periods of a couple of days when temperature is normal, followed by periods of fever.
What is the relationship between heart rate and temperature?
An elevation of 1˚C results in an increase of 15bpm.
What is the physiology of thermoregulation?
• The Hypothalamus is the body’s thermostat.
- Heat sensitive receptors are located in the preoptic area in the anterior part of the hypothalamus.
- An increased temperature (Above 37.1) causes increased signal output whilst a decreased temperature causes a decreased signal output.
- With elevations in core temperature the sympathetic nervous system is inhibited leading to vasodilation of skin vessels and stimulation of sweat glands to reduce temperature.
evaporative heat loss until body temp matches set point
There are four stages of a fever, what are they?
1) Prodromal phase.
2) Chill stage.
3) Flush Stage.
4) Defervescence.
What occurs during the Prodromal phase of a fever?
Non-specific complaints such as malaise, headaches, fatigue and aches.
What occurs during the chill stage of a fever?
There is an uncomfortable feeling of being cold, and shivering sets in. It is normally precipitated by vasoconstriction and piloerection. When shivering causes the body reach the new set-point a sensation of warmth develops.
What occurs during the flush stage of a fever?
Vasodilation occurs, causing the individual to feel warm and look flushed.
What marks the defervescence stage of a fever?
The onset of sweating.
What is the most studied exogenous pyrogen and where does it come from?
Lipopolysaccharide, it is derived from the cell walls of gram-ve cell walls.
What is the mechanism of fever?
• Exogenous or endogenous pyrogens bind to TLRs on monocytes and dendritic cells.
- This stimulates the formation of pyrogenic cytokines such as IL-1,-2 & -12, TNF-alpha and INF.
- These cytokines act on the thermoregulatory centre causing an increase in the prostaglandin, PGE2, which modifies the responsiveness of thermosensitive neurones.
Which two substances are endogenous antipyretics?
- IL-10 and glucocorticoids.
- They compete with IL-6.
How do NSAIDS and aspirin, reduce fever?
They both inhibit the production of PGE2.
- NSAIDS - Inhibits the activity of COX2, which enables the production of PGE2.
- Aspirin (and other salicylates) - As above but irreversibly inhibits COX2.
Provide some evidence as to why fever may be beneficial.
- It is widespread among animals, would not be preserved by evolution if it was not beneficial.
- IL-1 (an endogenous pyrogen) is critical for the initiation of the immune response.
- Small elevations in temperature (such as those in fever) aid the function of some immune responses.
- Many microbes function best at **normal **body temperature.
- Raised body temp. inhibits growth of bacteria and viruses.
How does Hyperthermia differ from fever?
Hyperthermia is an increase in body temperature without a change to the thermoregulatory set-point. Therefore, antipyretics are of no use.
What is the definition of Pyrexia of Unkown Origin?
A consistently increased temperature above 38.3˚C for three weeks, with no diagnosis after three days as an inpatient or 3 outpatient consultations.
What type of cell is this? What is it’s function?
Monocyte - Macrophage (In tissue)
- Recruited to sites of infection, very numerous in sites of infection.
- Mononuclear-phagocytic system.
- First contact with foreign antigen, initiate immune response through cytokines.
What type of cell is this? What cell line is it derived from? What is its function?
Neutrophil
- Polymorphonuclear leukocyte
- From the bone morrow, myeloid stem cells.
- Granules contain enzymes, responds to chemoattractants, phagocytic.
What type of cell is this? What cell line is it derived from? What is its function?
Basophil/ Mast cell(In tissue)
- Polymorphonuclear leukocyte.
- Myeloid stem cells.
- Contain histamine, have Fc receptors for IgE, important role in hypersensitivity / anaphylaxis.
What type of cell is this? What cell line is it derived from? What is its function?
Eosinophil
- Polymorphonuclear Leukocyte.
- Myeloid stem cell line.
- Produces histaminase and has an important role against helminths.
