NURS 330: Patho-Thermoregulation

Body Temperature Regulation

  • The human body maintains a constant temperature range of between 97 and 99 degrees Fahrenheit, with an average temperature of 98.6 degrees F.
  • Temperature regulation is accomplished primarily by the hypothalamus, a part of the brain.
      - The hypothalamus responds to information received from thermoreceptors located in the skin and internal organs.

Hypothermia

  • Definition: Body temperature below 95 degrees F (35 degrees C).
  • Mechanism of Regulation During Hypothermia:
      - Thermoreceptors detect decreased body temperature.
      - They send signals to the hypothalamus to take corrective action to increase body temperature.
      - Hormonal Response:
        - The hypothalamus increases secretion of thyrotropin releasing hormone (TRH).
        - TRH travels to the anterior pituitary gland, stimulating the secretion of thyroid stimulating hormone (TSH).
        - TSH is carried by the bloodstream to the thyroid gland, leading it to secrete thyroid hormones T3 and T4 (thyroxine).
        - These thyroid hormones accelerate the body's metabolism, helping to generate heat.
      - Effects of Thyroxine:
        - Promotes the release of epinephrine (adrenaline) from the adrenal medulla, further increasing metabolic rate and promoting heat production.
      - Other Responses:
        - The hypothalamus stimulates the sympathetic nervous system to:
          - Increase muscle tone.
          - Induce shivering, which generates additional heat.
      - Peripheral vasoconstriction occurs to maintain core body heat.
Behavioral Responses to Hypothermia
  • The cerebral cortex receives information regarding the drop in body temperature and influences behaviors to conserve heat, such as:
      - Adding more clothing.
      - Seeking warmer environments.
Risks and Consequences of Hypothermia
  • Causes depression of the central nervous and respiratory systems.
      - Vasoconstriction resulting in possible ischemic tissue damage (lack of blood supply).
  • The Lewis phenomenon: A response during hypothermia that helps keep extremities oxygenated by allowing temporary reperfusion.
  • Progression of hypothermia can lead to:
      - Shivering to stupor.
      - Decreased cardiac output.
      - Acidosis.
      - Ventricular fibrillation.
      - Potentially death.

Hyperthermia

  • Definition: An increase in body temperature above normal ranges.
  • The hypothalamus works to counter elevated body temperature by:
      - Inhibiting TRH secretion, which slows metabolism.
      - Decreasing muscle tone and shivering.
      - Increasing breathing rates to enhance heat exchange with the external environment.
      - Activating sweat glands to produce sweat, which aids in cooling through evaporation.
      - Peripheral vasodilation: Blood vessels widen, facilitating heat transfer from the core to extremities.
Mechanisms of Heat Loss
  • Heat can be lost through several transfer mechanisms:
      - Radiation: Transfer of heat from warmer to cooler areas (e.g., stepping into an air-conditioned room).
      - Conduction: Direct heat transfer from a warmer object to a cooler object (e.g., touching a cool surface).
      - Convection: Heat carried away by air or fluid currents (e.g., using a fan).
      - Evaporation: Heat is carried away as sweat evaporates from the skin.
Vulnerability to Temperature Changes
  • Infants may struggle with temperature regulation due to:
      - Small body surface area.
      - Lower levels of insulating adipose tissue.
      - Limited ability to sweat and shiver.
      - Greater peripheral vasoconstriction in cold conditions.
  • Elderly individuals may face challenges due to:
      - Lower metabolic rates.
      - Decreased blood circulation.
      - Impaired sweating ability.
      - Presence of chronic diseases.
Consequences of Hyperthermia
  • Damage to nerves and coagulation of cell proteins can occur in severe cases.
  • Temperatures reaching or exceeding 105.8 degrees F (41 degrees C) can lead to convulsions.
  • Types of Hyperthermia:
      - Heat Exhaustion:
        - Symptoms include profuse sweating and vasodilation leading to:
          - Dehydration.
          - Decreased blood pressure.
          - Electrolyte imbalances.
      - Heat Cramps:
        - Characterized by muscle cramping due to excessive sweating and sodium loss.
      - Heat Stroke:
        - Results from prolonged stress on the thermoregulatory centers, leading to:
          - CNS degeneration.
          - Confusion and coma.
          - Potentially death.