14) Control of Body temperature

• When core temperature increases above normal, heat loss mechanisms such as sweating, vasodilation, and radiation increase to cool down the body.
• Thermoregulation engages multiple physiological systems:

  1. circulatory
  2. Endocrine
  3. integumentary (skin)
  4. Musculoskeletal
  5. Nervous

  
• Homeotherms:

  • Maintain constant body temp regardless of external conditions
  • High energy and inefficient

  Poikilotherms:

  • Body temp fluctuates with environment
  • Uses less energy but unable to adapt to new environments
• Some homeotherms hibernate to generate heat without using much ATP.

  • This builds brown fat which generates 10x more energy than white fat

  
• The hypothalamus plays a key role in body temp regulation:

  • 37c is the optimal temp for catabolic and anabolic enzymatic reactions
• Anabolic: Building up molecules and structures, requires energy.

  Catabolic: Breaking down molecules for energy, releases energy.
• Core temp can be measured accurately with a thermometer in the

  • Tympanic membrane (Ear canal)
  • sublingual area (Under the tongue)
  • rectum
• Blood vessels play a critical part in regulating body temperature:

  • blood vessels are lined by smooth muscle
  • recieve signals from nerves that regulate their contraction (Vasoconstriction) and regulation (Vasodilation)
  • Controlling blood flow and heat exchange with the environment.
• Heat gain:

  • Exothermic enzymatic reactions (eg: Breaking down food)
  • Skeletal muscle activity
  • Radiation
  • Artifical Heating
• Heat loss:

  • Convection (to air)
  • Conduction (if objects are cooler than us)
  • Evaporation
• Core body temperature is maintained by:

  1. Sensors (neural)
  2. Hypothalamus
  3. Effectors
• • The Hypothalamus has neurons that monitor core temp
  • It recieves additional input from other sensors (such as walls of great veins, skin, abdominal viscera) which all goes through the spinal cord
• Effectors include:

  • Skin arterioles
  • Sweat glands
  • Involuntary and Voluntary Skeletal muscles (eg: shivering/behaviour)
• The autonomic nervous system maintains homeostasis by co-ordinating organs:

  • Sympathetic promotes stress
  • Parasympathetic promotes relaxation
• Temperature is sensed in the skin by:

  • Naked nerve endings
  • Cold sensing fibres
• When the body is cold we ”Shiver”

  • This stimulates blood circulation
  • Increases heat loss through convection
• At 0<35C thermoregulatory responses are inactivated and marks the start of hypothermia