essay 17 - fever - aetiology and pathogenesis, Fever significance. Fever stages. Metabolism with fever. Alterations in organ and system functions

and what is a fever

• an increasing body temperature due to activation of the thermal regulatory centre in hypothalamus. It is caused by pyrogens, these are fever inducing substances.

• the normal human body temperature is 37 degrees Celsius, a temperature over 38 degrees is considered a fever

describe the types of pyrogens

• exogenous Bacterial pyrogens = bacterial toxins (gram negative bacterial)

• exogenous non bacterial pyrogens = toxic elements, transfusion reactions

• Endogenous pyrogens = interleukin 1 and 6, tumor necrosis factor alpha, interferon alpha

pathogenesis of a fever

1. pyrogen release

2. hypothalamus is stimulated and released prostaglandin E2

3. PGE2 raises a set point in the Hypothalamic Thermoregulatory Centre

4. effector responses = vasoconstriction, shivering, increased metabolism to generate heat

why is a fever significant

• it enhances immune defence, restricts microbial growth (as many microbes prefer 37 degrees), and supports tissue repair, but it also places a heavy metabolic load on the body. In healthy individuals it is usually protective, whereas in vulnerable patients (infants, elderly, cardiac or pulmonary disease) or at very high temperatures, it can be harmful or life threatening

stages of fever

1. increase in body temperature ( stadium incrementi)

• onset phase

• hypothalamus raises the temperature setpoint

• consequence = chills, vasoconstriction, shivering

2. increased body temperature (stadium fastigili)

• plateau phase

• body maintains high temperature

• consequences= increased metabolism, hyperventilation, tachycardia

3. decrease body temperature ( stadium decrementi)

• heat dissipation

• set point returns to NORMAL

• consequences consequences= vasodilation, sweating

metabolism with fever

• Increased BMR = roughly 10% increase for each degree increase

• carbohydrate metabolism = increased glucose utilisation

• protein metabolism = increase Protein catabolism

• lipid metabolism = Increased lipolysis for energy supply

• water and electrolyte balance = dehydration, hyponatremia, potassium lost via sweat

alterations in organ and system functions

• cardiovascular = tachycardia, increased cardiac output, risk arrhythmia in heart disease

• respiratory = hyperventilation, Increased oxygen consumption

• nervous system = headache, delirium, seizures

• renal = decrease urine output (due to dehydration, ADH release)

• GI system= loss of appetite, nausea, Constipation