Thermoregulation Flashcards
What is the normal range for body temperature?
36ºC-37.5ºC
What is thermoregulation?
The processes involved in maintaining balance between heat production and heat loss
What is a temperature “Set Point”
The body temperature that the hypothalamus sets as “normal” and attempts to regulate body temperature around
Where are core body temperatures typically measured?
Tympanic (Ear drum) or Rectal sites
Where are surface body temperatures typically measured?
Oral or sublingual sites
What are four mechanisms of heat transfer?
Conduction, Convection, Radiation, Evaporation
How does conduction heat transfer work? What is a practical example of this?
Molecules in a substance or molecules in two objects in contact with each other transmit their kinetic energy to neighbouring molecules by colliding with them. The mediums themselves don’t move. A practical example of this would be hot and cold packs.
How does convection heat transfer work? What is a practical example of this?
The heated molecules of a medium move to other areas. When a hot medium flows into a cold medium, the hot medium will heat the cold and vice versa. A practical example of this would be blood becoming heated as it passes through our internal organs and taking that heat towards our skin to be cooled.
How does radiation heat transfer work? What are some practical examples of this?
Electromagnetic waves carrying energy from one place to another. Examples of this are the sun and light bulbs.
How does evaporation/vaporisation heat transfer work?
The change in state of water from liquid to vapour results in the loss of heat from the surrounding environment.
What are some behavioural processes of heat loss?
Staying still
Staying/moving into the shade
Turning on air conditioning if available
Wearing less clothing
What are some behavioural processes of heat retention/gaining?
Huddling
Curling into a ball (minimises surface area for heat loss)
Putting on more clothes
Using a heating device if available
What are the physiological responses to cause heat loss?
Vasodilation near skin, Decreased metabolic rate and Sweating
Is vasodilation controlled by the sympathetic or parasympathetic branch of the autonomic nervous system?
Parasympathetic autonomic nervous system
How does vasodilation in the skin promote heat loss?
Heated blood is carried to the skin, then the heat is lost through the skin, cooling the blood at the same time
What causes metabolic rate to decrease?
Reduced secretion of thyroxine
How does a decreased metabolic rate promote heat loss?
Less energy being used for metabolism produces less heat energy
Is sweating caused by the sympathetic or parasympathetic branch of the autonomic nervous system?
Sympathetic autonomic nervous system
What electrolytes and body byproducts are found in sweat?
Sodium chloride, urea, lactic acid and potassium ions
What are the physiological responses to cause heat retention and gain?
Vasoconstriction near skin, Increase in metabolic rate and Shivering
Is vasoconstriction controlled by the sympathetic or parasympathetic branch of the autonomic nervous system?
Sympathetic autonomic nervous system
How does vasoconstriction in the skin promote heat retention?
It prevents heat loss through the skin and keeps internal organs warm
What causes metabolic rate to increase?
- The hypothalamus stimulating the adrenal glands to secrete adrenaline and noradrenaline
- The hypothalamus stimulating the anterior pituitary to secrete thyroid stimulating hormone, acting on the thyroid gland to release thyroxine
Both of these cause metabolic rate to increase
How does an increased metabolic rate promote heat gain?
More energy being used for metabolism produces more heat energy
What triggers shivering?
Hypothalamus stimulates regions in brain involved in skeletal muscle toning
How does shivering promote heat gain?
Muscles contracting 10-20 times per second generates friction within the muscles and therefore heat
What is piloerection?
A vestigial bodily function which raises the hairs on our skin to make goosebumps to trap an insulating layer of still, warm air next to the skin (more useful in animals with long fur than in humans)
What is the control centre for thermoregulation?
The anterior hypothalamus
Where does the anterior hypothalamus receive thermoregulatory information?
Thermoreceptors in the hypothalamus monitoring blood temperature of blood going to the brain and thermoreceptors in the skin
What is a fever?
A bodily defence mechanism against invading microorganisms where body temperature may increase by 2-3ºC.
What are the 3 stages of a fever?
The chill phase, plateau phase and defervescence (breaking) phase
What occurs in the chill phase of a fever?
The hypothalamus sets a high temperature set point, so the body begins to feel cold and commences physiological heat production and retention responses
What occurs in the plateau phase of a fever?
Core body temperature reaches the new high temperature set point and the individual may fluctuate between feeling really hot and really cold
What occurs in the defervescence (breaking) phase of a fever?
The hypothalamus resets the temperature set point to a normal temperature, so the body commences physiological heat loss mechanisms. The individual may look red, flushed and sweaty at this time
What is the difference between pyrexia (fever) and hyperthermia (heat exhaustion/stroke)?
In pyrexia (fever), the body increases and decreases its temperature set point and its physiological thermoregulatory mechanisms are able to bring the body to the changing set point In hyperthermia, the set point doesn't change and it's the inability of the body's physiological thermoregulatory mechanisms to reduce the body's temperature to the set point.
What can result from an elevated body temperature?
Fluid loss and dehydration Electrolyte imbalances Decreased urine output Increased physiological demands Tachycardia and tachypnea Cellular/tissue damage (if temp to high or high for too long) - neurological damage Confusion/delirium - febrile convulsions (especially in children)
What is hypothermia?
When body temperature is less than or equal to 35ºC due to thermoregulatory mechanisms being insufficient to raise body temperature or impaired hypothalamic regulation, causing bodily chemical reaction rates to slow.
Can also be induced during surgery while being closely monitored
What is frostbite?
The formation of ice crystals inside cells at temperatures below 0ºC, causing permanent circulatory damage
What is the treatment for fever?
To support the physiological mechanisms for each stage of the fever (warm or cool the patient depending on the stage)
Promote comfort (e.g. antipyretic medications)
Monitor fluid, nutrition and electrolytes
- Hydration and electrolyte therapy
Remove the cause of infection
What is the treatment for heat exhaustion/stroke?
Facilitate cooling mechanisms
Rehydration
Monitor for further complications
What is the treatment for hypothermia?
Rewarming methods
Close monitoring of body temperature
What is the treatment for frostbite?
Gradual rewarming
Analgesia (pain management)
Protection of injured tissue
How does Panadol and other antipyretics reduce fever?
Acetaminophen inhibits prostaglandins, returning the temperature set point to a normal level
