Cold Lecture Flashcards
What are the 3 types of environmental temperature variations and what do they mean?
- Circadian: The internal regulatory cycle occuring over a 24 hour period
- Circannual: Occuring over the period of a year
- Geographic: Changing with location
What is the body core temperature range?
- 36-38 degrees celcius
Where does most of the heat in the body come from?
Metabolic heat production
What is the definition of the thermoneutral zone
“The range of ambient temperature in which normal metabolism provides enough heat to maintain an essentially constant body temperature in homeothermic animals” Essentially its the ambient temperature that the body only requiers basal metabolic rate (BMR) in order to thermoregulate
How does the body thermoregulate in the TNZ?
- Basal Metabolic Rate (BMR)
- Body temp is regulated by altering heat loss through the skin
How does peripheral vasoconstriction/dilation affect the TNZ?
- Vasoconstriction: Reduces the amount of blood moving from deep (warm) areas of the body to the skin, therefore less heat will be lost to the environment
- Vasodilation: The damn opposite
What is the lowest temperature within the TNZ known as? how does the body combat this?
The Critical temperature (technically the Lower Critical Temperature)
- Below this temperature, metabolic heat production has to be raised to offset heat losses
What are the two types of temperature-sensitive receptors? Where are they located?
Peripheral receptors:
- Skin and some mucous membranes
Central receptors:
- Hypothalamus, spinal cord, around central great vessels
What are the two types of peripheral receptors? What stimulates each and what fibres are utilized?
COLD:
- Simulated by a “lower range of temperature” - wowie
- between about 15-30 degrees celcius (below this its accompanied by pain)
- A-Delta fibres
HOT:- Stimulates by a “higher range of temperatures” - double wowie
- between about 30 -45 degrees celcius (above this the signal is accompainied by pain)
- C Fibres
What temperature range do cold receptors detect?
15-30
What temperature range do warm receptors detect?
30-45
What type of afferent nerve fibre is a cold receptor
A-Delta
What type of afferent nerve fibre is a hot receptor?
C Fibre
Which temperature receptors do we have more of (Between hot and cold)? Why?
Cold.
From an evolutionary POV, modern man came from the warmer areas of Africa, thus it was much hotter.
Thus we have less receptors to deal with heat as we were more sensitive to cold.
Where are warm thermoreceptors usually located?
Hypothalamus
Which regions of the hypothalamus are concerned with heat loss? Associated mechanism?
Anterior hypothalamus (Pre-Optic area) (Vasodilation)
What 4 body mechanisms increase heat production?
- Increased Activity
- Non-Shivering Thermogenesis
- Metabolic Acclimatisation and Adaptation
- Increased Feeding
What are the four mechanisms of decreased heat loss?
- Behaviour
- Insulation
- Cutaneous vasoconstriction
Vascular acclimatisation and adaption
Main body mechanisms in cold thermoregulation
Redistribution of blood to or away from periphery
What region of hypothalamus is concerned with heat gain? What is the associated mechanism?
The posterior hypothalamus.
Shivering and vasoconstriction
Clinical definition of hypothermia?
Any core body temperature lower than or equal to 35 degrees. That is mild, moderate is anything below 33, then severe is anything below 28.
What is shivering?
- Autonomic and continuous conctractile muscles of the skeletal muscles.
- The uncoordinated pattern of activity in which muscle fibres contract and relax out of phase of each other
- Usually in extensor muscles, proximal muscles of the upper limbs and trunk.
Why do peoples teeth chatter in cold?
The jaw muscles start to shiver; masseater + temporalis.
Why is brown adipose tissue significant?
Heat producing tissue.
Which animals have is Brown adipose tissue and where is it located?
Hibernating animals.
Usually in neck, paravertebral and mediastinal regions
How does brown adipose tissue increase heat production?
Skeletal muscle is 2 watts per kg, BAT is 300 watts per kg if broken down
BAT has a lot of mitochondria that actually don’t produce ATP, instead just produces A LOT of heat.
What stimulates activation of brown adipose metabolism?
Extreme cold -> physiology it has to do with noradrenaline, more a SNS response
Target cell responses to thyroid hormones
- increase the production of mitochondria
- increase number of Na-K ATPases, essentially lifting the basal metabolic rate
By how much does shivering increase body heat production in humans?
5x
What provides main stimulus for shivering?
Skin receptors
What hormones can increase heat production?
T3 T4,
cortisol
glucagon
adrenaline
insulin
ACTH
Target cell response of thyroid hormones (heat gain)
Increase production of mitochondria
Increase number of Na-K ATPases, essentially lifting the basal metabolic rate.
What happened to the Australian Antarctic team ?
Before departure, cold chamber test in melbourne -> core temperature test decreased core temperature.
After 6 months in antarctic, c
What is the underlying mechanism of long term adaptation to cold climates in humans.
Increased metabolic response to cold temperatures due to enhanced non-shivering thermogenesis.
What are 2 cold-dwelling populations?
Eskimos and Akaluf Indians of Tierra del Fuego.
How do Alakaluf Indians traditionally sleep?
Naked in simple shelters at 2-5 degrees C (No shivering)
Describe the basal metabolic rate of Alakaluf Indians?
30-40% high than other populations
Describe Eskimo lifestyle?
High protein/fat diet.
Lots of Vit D from fish eyes.
High body fat w/ short stature.
How does increased feeding and high protein diet increase heat production?
Digestion of protein requires more energy which in turn increases metabolism when consumes. This subsequently means heat production in increased. (Cold increases apetite).
What physiological mechanism accompanies increased metabolism when feeding? What is the consequence of this?
Increased blood flow to the peripheral regions of the body.
Inevitably increases heat loss to environment -> reduces thermoregulatory contribution of feeding
How can behaviour decrease heat loss?
By reducing surface area exposed to cold. i.e, more clothing, hugging self
What do animals have that we don’t which assists with insulation?
Fur. (Insulation layer of warm air)
What evolutionary adaption do humans have to make up for hairlessness?
Goosebumps
Mechanism of goosebumps:
Erector pillae muscles of hair follicles contracting to bring up hair = increases insulation
What is CLO?
A uniform unit which helps describe insulation factor of clothing. (1 CLO = business suit)
Why must outer garments not be completely impermeable to water when trying to reduce heat loss?
Insulation value of clothing decreases due to condensation and possible freezing of evaporated sweat.
What is the primary physiological response to environmental temperature decrease?
Peripheral vasoconstriction
What is the Hunting Reaction?
That is, at very cold temperatures, our blood vessels dilate, they bathe our poor, vulnerable skin in nice, warm blood arriving from our warm innards. This process prevents our skin from freezing and being damaged.
Why is the Hunting reaction called Hunting reaction?
The hands are essential for hunting/surviving, thus the need for BF to them overrides heat conservation driven vasoconstriction
Example of vascular acclimatisation and adaption?
Local acclimatisation in those frequently expose to cold in extremities: Less severe vasoconstrictor response
Eskimos exhibit higher than normal rate of peripheral blood flow
What is Topor?
Behavioural and physiological state of inactivity and reduced metabolic rate.
In a way is sort of like hibernation but less extreme and for shorter periods of time; only lasts for a few days.
What is hibernation?
Overall reduction of core body temperature to almost ambient levels -> reduces metabolic rate and thus keeps them alive when food is scarce in cold areas
Which animals hibernate?
Bears
Squirrels
Bats
Wood chucks
How does hibernation work physiologically?
Very Precise:
- Brown adipose tissue thought to have hormonal component
Changing temperature/light switches on hormonal stimulation of BAT.
Water loss reduces heat storage of body and freezing of tissue.
Arousal from hibernation description:
Arousal from this state is quick, about 90 min, using shivering and non-shivering thermogenic processes. The stimulus for arousal is thought to be temperature driven.
Reduced temperature of icefish - why and how?
They live in an extremely cold environment (-1.8-2 degrees C underwater).
- O2 carried around in the plasma. Fish has very low metabolic rate
- O2 has much higher solubility in water at the lower temperatures present here
- CVS: Compensation for lack of Hb, they have larger BV’s, greater blood volume, larger hearts and greater CO. No coronary arteries, they absorb O2 from the blood they pump.
- Low viscosity blood prevents a lot of problems brought about by an increase in BV.
- Only vertebrates known to lack Hb as adults (part of that fish group)
Describe supercooling in insects? Mechanism, issues and solutions
Grasshoppers have sphericles: little holes in the exoskeleton that allow air in, kind of like gas capillaries
How they get rid of O2 and get CO2
Problem with cooling insects is that the liquid in their systems can form ice which damages body membranes.
Their strategy is freeze avoidance or freeze tolerance
Freeze avoidance they attempt to lower the freezing point of body fluids by having liquids inside the body that prevent water freezing e.g. by having ethylene glycol in there or glycerol
European vs Aboriginal Persons response to cold:
Why?
Cold exposure =
Europeans: cor maintained at 36˚C.
Aboriginals: Core temperature fell below 35˚Cw without heat loss compensatory mechanism activation.
Aboriginal people can afford to cold down during night as Aus sun will warm them up in the morn.
What occurs to body at core temp <35˚C?
Core below 35˚= muscular weakness -> decreased mobility (and shivering) thus core temp rapidly falls.
What occurs to body at core temp <34˚C?
Mental confusion and visual disturbance.
At what (cold) core temperature would one lose consciousness?
32-30˚C
Most important effect of hypothermia? Why?
Effect on heart:
Core <28˚C = cardiac arrhytmias and v-fib .
Slows pacemaker and decreases cardiac output. Thus coronary/cerebral circulation affected.
Why is being physically fit good in preventing hypothermia?
Muscle metabolism increased = better heat production to offset heat loss. Maintained longer without fatigue.
Human survival stories in cold.
Anna Bågenholm core body temp reached 14˚C brought back from dead
What is Raynaud’s Phenomenon?
When extremities of the body have reduced BF (fingers, nose, ears, etc.) and they feel very cold. Exaggerated vascular response to stress or cold.
What are chillblains?
Painful inflammation of small BV’s that occurs when exposed to cold but not freezing air. Blisters and painful (lol I know right, Jacs toes get absolutely rekt in winter)
What is frostbite?
Freezing of peripheral tissues -> necrosis.
Pathophysiology of frostbite:
Damage results from mechanical action of ice crystals and cell dehydration..
-> Ice forming in cells reduces water content thus increased osmolarity.
BV permeability also increases.
Thawing = loss of fluid from circulation into tissue space
Cold what hypothermia? Explain
Heat conduction of water is increased. Thus it sucks the heat from you way faster than air does. Being fatter is better for survival.
Cryosurgery: Minor and cosmetic procedure:
Wart removal, mole removal, skin tag removal
Cryosurgery major procedures (list)
Cancer therapy, heart surgery (cryopreservation).
