Hot Flashcards
Where are central warm receptors located?
Primarily in the hypothalamus but some in great vessels.
What is the upper degree of the TMZ?
31˚C
What causes ‘disturbance’’ to body at temperatures >31˚C?
Heat gain from environment and metabolic processes exceeds heat loss resulting in increased core temperature.
How much energy is used to transform water into water vapour (sweat stuff)?
2400kJ/litre
What is the most efficient mode of heat loss?
Evaporation
Clinical definition of hyperthermia?
Temperature of the body gets above 41 degrees (proteins will start to denature above this, thus can be fatal)
What are the two ways in which the body responds to high temperatures?
Increase heat loss
Decrease heat gain
What is the only way the body has to immediately decrease heat gain?
Behavioural Choices: reducing activity, Inertia, apathy, decrease skeletal muscle use.
Eat less
What is aestivation?
Some mammals reduce their activity to zero in the summer months & remain dormant in their burrows, thereby reducing the costs of staying cool. = reduces metabolic needs and BMR to survive heat with minimal food and work.
Which animals aestivate?
Bees, snails, crocodiles, frogs, snakes, lemurs, lungfish, cane toads
What physiological changes allow an animal to aestivate?
- metabolic rate is reduced, water can be retained
- problem then is the buildup of nitrogenous waste
2 main mechanisms to increase heat loss
Evaporative cooling: (sweating and panting)
Peripheral vasodialtion
How are body shape and heat loss related?
Large surface area for low weight increases abilty of body to lose body heat via evaporative cooling.
What form of body heat loss does being leans specifically facillitate?
Conduction of heat from deep tissues to periphery (less distance to travel).
What are the two population of people Phil mentioned in relation to being really tall and living in a hot place?What is their average height?
Nilotic people of Sudan and the Masai of Kenya.
Average male 2.14m tall.
Average amount of sweat glands per cm2?
Total body averages 120 sweat glands per cm2 but this is not evenly distributed.
What % of sweat comes from glands on chest and back on humans?
50%
What is maximum sweat rate in man? What is this equivalent to in kj/hr and xBMR?
3L/hr but this is not sustainable.
7000kJ.hr
20x BMR
What is the average sweat rate for a man working in hot dry conditions per day?
12 litre/day.
Do men or women have higher average sweat rates?
Men
Physiology of sweating:
- SNS stimulation causes the eccrine sweat glands to secrete aqueous solution to the skins surface
- There are also apocrine glands that are adrenergically innervated and secrete during excitement and anticipation
Physiological difference between sweating at high an low rates (composition of sweat etc).
- Sweating slowly will produce diluted sweat as there is more time for absorbtion of ions from sweat in the glands. Very hypotonic
- Sweating profusely the secretion is much closer to isotonic as there isnt as much time for ions to move back into the glands.
What is the main disadvantage of sweating and how can this be offset?
Loss of water and electrolytes.
Consume water with electrolytes lol
What environmental factor grossly affects effectiveness of sweat? Why?
Humidity - The air is already somewhat saturated with water, thus it cant take more on and evaporative heat loss cant occur like usual.
What feature of the body facilitates sweat use?
Hairlessness of body
How long does it take for someone to fully acclimate to desert environments?
1-2 Weeks
What does acclimation to a desert environment entail?
Increased sweat rate
Lower sweating threshold
Decrease in salt concentration in sweat
What is hyperhydrosis? Cause?
Excessive sweating unrelated to heat or exercise.
Unknown cause but rumoured to be SNS activity. Can be triggered by some foods and medications.
What was sweating sickness?
Random epidemic that occured in europe over the late 15th century
they had bad sweating symptoms which would lead to death within 3-18 hours.
cause is unknown, may be linked to bacterial infection as a result of poor sanitation.
How do animals lose heat via evaporative cooling? How does this work?
Panting
Increase evaporation from upper respiratory tract.
Advantages of panting over sweating?
- Panting provides own air currents to facilitate evaporation
- Does not result in loss of sodium in the way sweating does
Disadvantages of panting over sweating?
Increased ventilation → Increases work of breathing and alkalosis.
Underlying physiology of countercurrent heat exchanger?
The heat from warm arterial blood is passed onto the cooler venous blood (via conduction).
Examples of countercurrent heat exchanger?
- Testes
- African Antelopes have them at the base of the brain and nasal passages to keep the brain cool
- Seals, dolphins, whales all have heat exchangers on their fins (don’t have blubber on their fins, thus need it there)
- Tuna (generate a lot of heat due to speed, thus have heat exchangers to cool them down)
At what ºC does a camel start to thermoregulate to prevent hyperthermia?
41˚C
At what ºC does a African gazelle start to thermoregulate to prevent hyperthermia?
46˚C
How do camels cope with hyperthermia
- Allow their body temp to increase during the day, have temperature gradients in nasal passages to protect the brain from overheating
- store a lot of the heat they gain in the day in the fat in their humps then offload that during the night.
- Camel urine really stinks as they have much longer loops of henle, thus they can concentrate their urine much better than we can.
For a camel weighing 500kg, a rise in 4˚C corresponds to an increase in heat storage by …? This is the equivalent of saving how much sweat?
7000kJ
3L sweat
Kangaroo rats and thermoregulation…
- They do not drink water, instead get their water from O2 oxidation from food.
- They store a lot of food in their burrows, the grains absorb some moisture from the atmosphere and then they eat them
What are the three types of heat stress?
Heat stroke
Heat exhaustion
Heat collapse
What is heat stroke?
- Body overheating as a result of prolonged exposure to high temperature (exceeding 40 degrees core temperature)
- Loss of thermoregulatory control → sweating starts to fail, thus decreases (very bad sign)
Physiology and consequences of heat stroke:
- Loss of sweating ability
- Causes
- Rising of core temperature
- Denaturing of proteins
- Destabilising of phospholipids and lipoproteins
- CVS collapse
- Can lead to a coma then death
What is heat exhaustion?
Heavy sweating and elevated pulse as a result of overheating
Physiology and consequences of heat exhaustion:
Effects the ECF volume which thereby affects ICF volume
Causes nausea and vomiting:
- Causes fatigue and weakness
- Poor mental function
What is heat collapse?
- loss of consciousness due to heat and humidity exposure
- fatigue and dizziness as a result of increased heat
Physiology and consequences of heat collapse:
- excessive sweating and shunting of blood to the skin leading to decreased BF to the brain
- also if someone is standing their already impaired due to gravity → pooling of blood in the lower limbs
What is malignant hyperthermia?
Severe reaction to anaesthetics.
Causes severe muscle contractions, high fever, elevated HR
Physiology and consequences of malignant hyperthermia?
- Ryanodine receptor in skeletal muscles is abnormal, interferes with calcium regulation
- Treated using dantrolene
- Medication stops release of calcium
