Temperature and Other Vital Signs

Body temperature

Core body temperature

  • The temperature of the structures deep within the body
  • Homeostatically maintained at about 37.8 ℃

Normothermia

  • Optimum temperature for cellular metabolism and function
  • Shows diurnal variation
  • Altered by activity, emotions, exercise, exposure
  • Varies during menstrual cycle

Heat gain

  • Metabolic heat
    • Basal Metabolic Rate: basic level of heat production
      • Can be increased by hormones
    • Muscle activity - shivering
  • Radiation, conduction, convection, conduction

Heat loss

  • Radiation: emission of heat energy as electromagnetic waves
    • ½ body heat loss
  • Conduction: transfer of heat between objects in contact (warmer → cooler)
    • Depends on temperature gradient and thermal conductivity
    • Combines with convection
  • Convection: air next to skin warmed by conduction, warmed air is less dense and will rise while cooler air moves next to the skin
  • Evaporation
    • Passive: water passively diffuses from the surface of the skin and the linings of the respiratory airways
    • Active: sweating controlled by SNS

Maintenance of core body temperature

  1. Sensor detects change - central thermoreceptors, peripheral thermoreceptors
  1. Sends signal to hypothalamus
  1. Effectors (e.g. skeletal muscles, skin arterioles, sweat glands) triggered to respond and restore variable to normal

Hypothalamus

  • Temperature control centre
  • Posterior hypothalamic centre = activated by cold
  • Anterior hypothalamic centre = activated by warmth

Abnormal body temperature

Fever

  • The set point of the body’s core temperature has been raised (38-40℃)
 
  1. Macrophages release chemicals which act as an endogenous pyrogen
  1. Stimulates hypothalamus to release prostaglandins
  1. This ‘resets’ the thermostat to a higher temperature
  1. Hypothalamus initiates mechanism to heat body – cold response
  1. Thermostat reset to normal if pyrogen release reduced/stopped

Hyperthermia

  • Extreme uncontrolled increase in body temperature (due to failure of heat regulating mechanisms)
  • >40℃

Hypothermia

  • Drop in body temperature below that required for cellular metabolism and function
  • At or below 35℃