Thermoregulation Flashcards
What is “set point” ?
Desired value chosen by hypothalamus for core body temperature
What is core temperature?
36.7 C
Brain and visceral temperature
(In morning range = 36.3-37.1 C)
Where are thermoreceptors?
In skin viscera and brain
What can core temperature affect?
Enzyme activity, change cellular function
Where are brain thermoreceptors?
More warm or cold ones?
Relay info to?
Pre-otic and superoptic region of hypothalamus
3x as many warm ones
Relay info to other areas of hypothalamus
What do visceral thermoreceptors sense?
Sense threat to maintenence of core temp. Thru
Ingested food that could change body temp
Etc.
Where will visceral thermoreceptors relay info to?
Hypothalamus (superoptic and pre-optic regions)
Where are cutaneous thermoreceptors?
Unimodal or bimodal?
Warm or cold sensitive?
Axons in skin
Bimodal - can sense both touch and temp.
Both but 10x more cold sensitive ones
What will cutaneous thermoreceptors do?
Tell us about environmental conditions
How does the hypothalamus act to control thermoregulation?
Thru hormones, ANS, and behavior changes
What is the role of the hypothalamus in thermoregulation?
Controller of body temperature
Decides set point
integrates received info about current temp and makes changes based on that
What does anterior hypothalamus do in re: to thermoregulation?
Responds to HEAT with heat loss behaviors
What does the posterior hypothalamus do in re: to thermoregulation?
Responds to COLD w/ heat production behaviors
What gives us insulation?
Why is this the insulation material?
Adipose tissue
Bc 1/5 the thermal conductance as compared to skin, muscles etc.
What causes babies to lose heat more than adults?
Higher surface area to size ratio
How does metabolism contribute to heat generation?
Anaerobic metabolism breaks down Glucose to lactic acid and produces 4 atp in the process
What are the mechanisms for heat production? (4)
Ans
Endocrine
Muscular activity
Non-shivering thermogenesis
How does Endocrine system contribute to heat production?
Thyroxin
Epinephrine
How does the ANS contribute to heat production?
Sympathetics contract skin, reducing heat loss
How does Muscular activity contribute to heat production?
- Shivering (increased motor neuron excitation)
2. Increased voluntary activity via cortex (running, jumping)
What part of the brain controls shivering?
Dorsomedial posterior hypothalamus
the one that responds to cold with heat production behaviors
What are the ways Non-shivering thermogenesis contributes to heat production?
Hormonal influences
Increased food intake
Brown adipose tissue
How does hormonal influence contribute to heat production?
Thyroxin will increase metabolic rate
Epinephrine contraction of BVs
How does increased food intake contribute to heat production?
Increased metabolism —> heat produced
How does Brown adipose tissue contribute to heat production?
What will need to innervate it to start it’s contribution?
Low efficiency hydrolysis of ATP via uncoupling proteins
Sympathetic fibers Circulating epinephrine (adrenergic innervation)
Who is brown adipose tissue critical in?
Infants
How do brown and white fat compare?
White fat also has uncoupling proteins and can be activated by sympathetic innervation
What are the 5 mechanisms for heat loss?
Evaporative heat loss Convection Conduction Radiation Blood to skin
What is evaporative heat loss?
What are the 2 types?
Energy lost as water evaporates
- Insensible (respiratory/ panting)
- Sweating (controlled)
What is convection?
Movement of molecules away from contact (hot air rising)
What is conduction?
What is a common form of this?
Transfer of heat between objects in physical contact with one another
Commonly b/w you and walls
What is radiation’s contribution to heat loss?
Infrared radiation transfers heat between 2 objects NOT in physical contact
How does blood to skin help heat loss?
How much blood to skin determines how much heat to environment
What will activate sweat glands?
Sympathetic cholinergic
ach to muscarinic receptor
What is the strucutre of a sweat gland?
Coiled region near lots of blood vessels w/ duct leading to skin
How is sweat produced?
- Serum filtrated, included ions
2. Fluid to skin surface w/ reabsorption of water and sodium and Cl back to blood in duct
What happens along the duct of a sweat gland if there is a high flow rate?
High water is excreted
What happens along the duct of a sweat gland if there is a low flow rate?
Low water excreted
High Na
What happens along the duct of a sweat gland if there is acclimation?
Low Na due to aldosterone action
What is a fever?
Controlled increase in set point
body temp. Following orders of hypothalamus
When will a fever occur?
Why?
With an infection
Bc immune system will release cytokines
PGE2 —> EP3 receptor —> increase hypothalamic set point for temperature
What will the increased Temperature set point from a fever cause?
Increased heat production thru shivering and non-shivering thermogenesis (thyroxin and epi)
Decreased heat loss via loss of blood to skin, decreased evap. Heat loss
When the infection is gone, what happens to the hypothalamic set point that was raised do to fever?
Returns to normal and now the body temperature is higher than T set point
When the fever has broke, and body temp is now to high, what happens?
Decreased heat production (apathy, inertia, anorexia)
Increased heat loss
Conduction, convection, EHL (Sweating), insensible EHL (panting)
What happens to your set point during sleep?
Decreased set point = decreased body temperature
What happens to your core temperature during exercise?
What temperature can it reach?
Increased set point = increased temp
Up to 40 C
What will sympathetic cholinergic innervation of sweat glands cause?
Vasodilation of blood vessels
