Thermoregulation Mechanisms
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Questions and Answers

Which of the following is a behavioral response to cold temperatures?

  • Vasodilation
  • Erection of hair (correct)
  • Hyperventilation
  • Sweating

    • What is the primary mechanism of heat transfer in a counter-current heat exchanger?

  • Conduction (correct)
  • Evaporation
  • Convection
  • Radiation

    • What is the primary site of shivering in the body?

  • Medulla oblongata
  • Posterior hypothalamus (correct)
  • Anterior hypothalamic preoptic area
  • Primary motor center

    • Which hormone stimulates glycogenolysis and lipolysis in response to cold temperatures?

    <p>Adrenaline</p> Signup and view all the answers

    What is the effect of thyroxin on the body's metabolic rate?

    <p>Increases metabolic rate</p> Signup and view all the answers

    What is the effect of cortisol on blood glucose levels?

    <p>Increases blood glucose levels</p> Signup and view all the answers

    What is the primary mechanism of heat loss in cold environments?

    <p>Conduction</p> Signup and view all the answers

    Which of the following is a physiological response to cold temperatures?

    <p>Vasoconstriction</p> Signup and view all the answers

    What is the primary mechanism by which the body reduces heat gain?

    <p>Inhibiting mechanisms that cause heat production and behavioural responses</p> Signup and view all the answers

    What is the effect of vasodilatation of skin blood vessels on heat loss?

    <p>Increased heat loss</p> Signup and view all the answers

    What is the composition of primary sweat secreted by the acini?

    <p>Isotonic secretion of NaCl</p> Signup and view all the answers

    What is the effect of evaporation of 1ml of sweat on the body's heat loss?

    <p>Removes 0.6 K Cal of heat</p> Signup and view all the answers

    What is the characteristic of sweating in acclimatization to hot weather?

    <p>Increased sweat production with decreased NaCl loss</p> Signup and view all the answers

    What is the definition of fever?

    <p>Hyperthermia caused by resetting of the setpoint of the hypothalamus to a higher level</p> Signup and view all the answers

    What is the role of aldosterone in the sweating mechanism?

    <p>Increases NaCl reabsorption</p> Signup and view all the answers

    What is the characteristic of cold sweat?

    <p>Emotional sweating with vasoconstriction</p> Signup and view all the answers

    What is the recommended treatment for sun stroke?

    <p>Immediate cooling of the body by immersion in ice cold water</p> Signup and view all the answers

    What is the primary cause of tissue degeneration in cases of heat stroke?

    <p>Loss of fluids and sweat</p> Signup and view all the answers

    What is the effect of hyperthermia on the central nervous system?

    <p>Stimulation of the CNS, leading to tremors and convulsions</p> Signup and view all the answers

    What is the effect of increased body temperature on heart rate?

    <p>It increases heart rate by 10 beats/min for each 1°C</p> Signup and view all the answers

    What is the effect of vasodilation on blood pressure?

    <p>It increases systolic blood pressure and decreases diastolic blood pressure</p> Signup and view all the answers

    What is the effect of hypothermia on heart rate?

    <p>It leads to heart stop</p> Signup and view all the answers

    What is the effect of hyperthermia on respiratory rate?

    <p>It increases respiratory rate</p> Signup and view all the answers

    What is the effect of frostbite on digits and lobes of ears?

    <p>It leads to gangrene</p> Signup and view all the answers

    Study Notes

    Regulation of Body Temperature

    • Two mechanisms to regulate body temperature:
      • Decrease heat gain: by inhibiting mechanisms that cause heat production and behavioral responses such as apathy and anorexia
      • Increase heat loss: through vasodilatation of skin blood vessels and sweating

    Sweating

    • Sweat is a hypotonic secretion of NaCl
    • Center: preoptic nuclei in the anterior hypothalamus
    • Supply: eccrine sweat glands are supplied by sympathetic cholinergic fibers (blocked by atropine)
    • Sweat secretion: an active process in which the acini secrete isotonic sweat, but NaCl is gradually reabsorbed by the ducts to make it hypotonic
    • Cooling effect of sweat: each 1ml of evaporated sweat removes 0.6 K Cal
    • Sweat starts at environmental temperature of 32°C
    • Dribbling alone without evaporation does not lead to loss

    Acclimatization of Sweating

    • Acute exposure to hot weather: a person sweats 700 ml/h and loses 15-30 gm NaCl/day
    • After exposure to hot weather for 6 weeks: a person sweats 2000 ml/h and loses 3-5 gm NaCl/day
    • Cold sweat: an emotional sweating even with cold and vasoconstriction

    Disorders of Temperature Regulation

    • Fever (pyrexia): hyperthermia caused by resetting of the setpoint of the hypothalamus to a higher level
    • Counter-current heat exchanger: directs blood to deep veins, which run parallel to the arteries, to conserve heat

    Behavioral Responses

    • Putting on heavy clothes
    • Curling the body to decrease surface area
    • Erection of hair as an insulator for cold (sympathetic effect)

    Increase in Heat Production

    • Shivering: involuntary rhythmic contractions of the skeletal muscle to produce large amounts of heat
    • Center: posterior hypothalamus in the primary motor center for shivering
    • Shivering can be prevented by curare (neuromuscular blocker)

    Hormonal Thermogenesis

    • Adrenaline:
      • Stimulates the metabolic rate
      • Causes cutaneous vasoconstriction
      • Stimulates glycogenolysis
      • Stimulates lipolysis (of depot fat)
    • Thyroxin: stimulates the Thyroid Stimulating Hormone (TSH) to secrete thyroxin hormone, which increases the basal metabolic rate (BMR)
    • Cortisol: stimulates the blood glucose and metabolic rate

    Effect of Exposure to Heat

    • Exposure to heat stimulates the hypothalamus to regulate body heat balance
    • Loss of fluids and sweat may lead to circulatory shock and tissue degeneration
    • Treated by: immediate cooling of the body, sponge with alcohol, and antipyretic drugs

    Sun Stroke

    • Beside sweating and dehydration, damage of brain tissue by direct sun rays leads to severe fever
    • Treated by immersion in ice bath and drinking saline

    Physiological Changes Associated with Hyperthermia

    • Central Nervous System:
      • At first, hyperthermia stimulates the CNS leading to tremors and convulsions
      • Above 41°C, malfunction of CNS occurs leading to loss of reflexes and coma
    • Cardio Vascular System:
      • Increase heart rate by 10 beats/min for each 1°C
      • Increase in body temperature due to direct stimulation of SAN or cardio-accelerator centre
      • Increase cardiac output due to vasodilatation of peripheral arterioles
      • Increase systolic blood pressure and decrease diastolic blood pressure
    • Respiration:
      • Increased respiratory rate by stimulation of the central and peripheral chemoreceptors

    Hypothermia

    • A drop of body temperature to a low level with slow metabolic and physiologic processes
    • Causes:
      • Exposure to extreme cold water (ice water) for 20 minutes
      • Frost bite: exposure to extreme cold weather leading to freezing in lobes of ears and digits of hands and feet
      • Impaired regulation of body temperature by the hypothalamus, leading to sleepiness and even coma

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    Related Documents

    Control Of Body Temperature PDF

    Description

    This quiz covers the mechanisms of thermoregulation, including decreasing heat gain and increasing heat loss through vasodilation and sweating.

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