24A16: Exam Report

Temperature
(a) Define heat and temperature (15% of marks).
(b) Describe how body temperature is regulated (85% of marks).

75% of candidates passed this question.

(a) The definition of temperature and heat varies considerably in texts, so reasonable leeway was granted in marking this part.

(b) In this section the following information was expected; body temperature range; thermoneutral zone; sensors (including receptors, fibres, and tracts); central processing (the role of the hypothalamus including anterior and posterior portions); interthreshold range; and a detailed description of the efferent responses for either increasing or decreasing body temperature.

R1iii / 24A16: Temperature
(a) Define heat and temperature (15% of marks).
(b) Describe how body temperature is regulated (85% of marks).

(a)

  • Heat is kinetic energy in a system, measured in joules.
  • Temperature is a measure of the tendency of heat transfer or average kinetic energy, commonly measured in degrees or in Kelvin

(b)

  • Temperature regulation is a homeostatic function that acts to preserve normal cellular function.
  • Body temperature range is usually 36-37.4 degrees Celsius (although there is variation with menstrual cycles as well as disease states)
  • The thermoneutral zone is the ambient temperature range in which a naked human can maintain a stable core temperature without altering BMR (this range in increased for infants or people with higher BSA) – it is ~30-34degrees Celsius
  • The interthreshold range is the central temperature (37 +/- 0.2 degrees celsius) that is tightly controlled by thermoregulation – the range can be widened by anaesthesia/disease
  • The critical temperature is the temperature at which a significant change in metabolic activity can be seen to compensate for the altered temperature

Regulation occurs through;

Sensors

  • Both central / visceral peripheral thermoceptors
  • Peripheral thermoceptors in the dermis include;
    • Cold (bulbs of kraus)
    • Active between 15-30 degrees, with increased firing at lower temperatures
    • Transmission via A-delta-fibres
    • Hot (bulbs of rufini)
    • Active between 25-40 degrees, increased firing at higher temperatures
    • Transmission via unmyelinated c-fibres
  • Temperature is transmitted in the spinothalamic tract
  • →sensory fibres enter via the DRG, synapse, ascend / descend 1-2 levels via tracts of lissauer, before decussating and ascending to the thalamus in the SPT tract

Integration

Progressing occurs in the hypothalamus

  • The anterior hypothalamus is primarily responsible for detection and response to heat
  • The posterior hypothalamus integrates cold sensation/response

Effectors

Thermoregulation alter heat production/loss; (primarily mediated through autonomic control)

Response:

Cold

Heat

Behavioural
(related to heat loss via

  • Radiation
  • Evaporation
  • Convection
  • Conduction)
  • Seek shelter
  • Increased layers
  • Increased activity
  • Increased hunger
  • Seek shade
  • Reduce layers
  • Reduce activity

Sympathetic response:

  • Skin
  • Vascular
  • Vasoconstriction
  • Piloerection,
  • Shivering
  • THERMOGENESIS
  • Sweating
  • Vasodilation

Metabolic

  • Increased BMR
  • Specifically increased B3 mediated activation at brown fat → leading to uncoupled oxidation reactions releasing heat

Decreased BMR

Author: Brodie Farrow