Describe the physiological control of body temperature and the pathophysiology of fever in infection

- 36 to 37.5 degrees celcius.

What is the range of healthy body temperature?

- By product of metabolism.

- Determined by basal rate of metabolism, muscle activity, thyroxine etc.

Role of heat production in controlling body temperature

- Most heat is procured in deep organs of body.

- Heat is transferred to skin where it is lost to environment.

Role of heat loss in controlling body temperature

- Radiation.

- Conduction.

- Evaporation.

What are the 3 main mechanisms of heat loss?

- Coordinated by temperature regulating centres in hypothalamus.

- Anterior hypothalamus responds to increased temperatures.

- Posterior hypothalamus responds to decreased temperatures.

Role of hypothalamus in temperature regulation

- Anterior hypothalamus is activated.

- Stimulates thermoregulatory sweat glands leading to increased sweating.

- Causes vasodilation leading to increased heat loss.

Describe what happens in regards to the hypothalamus following an increase in body temperature

- Posterior hypothalamus stimulated.

- Increased catecholamine production binds to BV's causing vasoconstriction.

- Arrestor pili muscles contract (cause hair on skin to stand up).

Describe what happens in regards to the hypothalamus following a decrease in body temperature

- When body temperature is above usual range.

- Caused by toxic substances affecting temperature regulating centres/abnormalities in the brain.

Describe fever

- Proteins, breakdown of proteins and other substances that cause body temperature set point to rise.

- They are released from toxic bacteria/degenerating tissues and hence cause fever in disease conditions.

What are pyrogens?

- Bacterial products stimulate IL-1 and TNF.

- These in turn stimulate cyclooxygenase enzymes which convert AA into prostaglandins.

- PGE2 stimulates production of neurotransmitters which increase temperature set point.

General summary of what causes fever

- Chills due to body temp being lower than that of the set point.

- Flush, when high set point is removed and body temp is suddenly higher than set point causing increased sweating and vasodilation.

- Heat stroke.

Characteristics of fever

- Cell membrane becomes unstable.

- Transport proteins cannot function effectively.

- Protein synthesis disrupted.

- RNA synthesis disrupted.

Cytotoxic effects of fever