Feedback Control: Temperature and other vital signs Flashcards
What is core body temperature?
The core body temperature is the temperature of the blood and internal organs
What is normothermia?
The optimum temperature for cellular activity and metabolism. Core body temperature is kept at this temperature by negative feedback control.
At what temperatures are fevers, hypothermia and hyperthermia classified?
Fever- 38-40 degrees
Hyperthermia- above 40 degrees
Hypothermia- below 35 degrees
What do you use to obtain an indirect core body temperature estimate?
Infrared tympanic (ear drum) thermometer or infrared forehead strips
What do you use to obtain a direct core body temperature estimate?
Rectal or oesophageal thermometer
What is diurnal variation?
The variation of body temperature throughout the day. For example, the CBT is at its lowest in morning and highest in evening.
How does the body lose heat?
- radiation
- conduction
- convection
- evaporation
How does the body gain heat?
- Metabolic heat gain
- radiation
- some convection and conduction
- muscle activity
What is the basal metabolic rate?
The minimum amount of energy required to sustain vital body functions which leads to heat production
What are the sensors in the maintenance of CBT?
Thermoreceptors
What are the two types of thermoreceptors?
- Central Thermoreceptors (found in hypothalamus, abdominal organs)
- Peripheral thermoreceptors (found in skin)
What is the control centre of the maintenance of CBT?
Hypothalamus
What part of the hypothalamus is activated by cold?
Posterior hypothalamic centre
What part of the hypothalamus is activated by warmth?
Anterior hypothalamic centre
What are the effectors in the maintenance of the CBT?
- Skeletal muscles
- Skin arterioles
- Sweat glands
What happens in the cold response?
- Vasoconstriction
- Skeletal muscles- Increase shivering, muscle tone and voluntary movement
- Other behavioural adaptations e.g. postural change and warm clothing
What happens in the hot response?
- Vasodilation
- Sweating (evaporation of sweat) by sympathetic
- Skeletal muscles- Decrease muscle tone and voluntary movement
- Other behavioural adaptations e.g. cool clothing
What is the pathway of a fever?
•infection or inflammation occurs
Chemicals (cytokines) released from macrophages act as an endogenous pyrogen
• Endogenous pyrogen stimulate the release of prostaglandins in the hypothalamus
• The prostaglandins act on the hypothalamic thermo-regulatory centre to “reset” the thermostat at a higher temperature
• The hypothalamus initiate mechanisms to heat the body “cold response” to raise the body temperature to the new set point
•The body temperature increases to reach the new set point resulting in “fever”
After a fever, how is the hypothalamic set point restored?
If the pyrogen release is reduced/stopped or the prostaglandins synthesis is decreased/ceased. The hypothalamus then initiates mechanisms to cool the body “hot response” to reduce the body temperature to the normal hypothalamic set point.
