Thermoregulation Flashcards
What is normal body temp?
36.7 (98.06)
Normal range - 36.3 - 37.1
Core temperature:
Temp of brain and viscera. Maintained over a range of environmental temperature (controlled variable)
Oral, hands and feet are variable
How does core temp change?
Core temperature varies throughout the day (1-2 degrees over 24 hour period
Low point at 6 in the morning
How do we know our core temp?
Thermoreceptors (skin, viscera and brain)
Different locations tell brain about different temps
What do the thermoreceptors watch out for?
Body temperature (Change in temperature affects enzyme activity, Change cellular function) Environmental temperature (threat to my temperature)
What type of thermoreceptors are sensing core temperature?
Brain (hypothalamic)
Viscera (tells you core temp as well as threats to your core temp)
What are cutaneous thermoreceptors?
Located on the skin.
Bimodal - temperature and touch sensitive
May be hot or cold sensitive (lots more cold sensitive)
tells us about environmental conditions
Why are there thermoreceptors in the viscera (e.g. gut)?
Need to sense threats to temp maintenance (food ingested can change body temp and need to tell hypothalamus about this)
Are there thermoreceptors in the brain?
Yes, on the pre-optic and superoptic region of hypothalamus
Sensitive to changes in temp, Lots more warm sensitive, relay info to other parts of hypothalamus about the temp of brain
Where do the thermoreceptors “report” their findings?
Hypothalamus (tells it hey this is the situation right now!)
Acts as the controller = thermostat
Why is the hypothalamus important for thermoregulation?
Has the connections to control hormonal (e.g. metabolism), autonomic (e.g. sweating) and behavioral (e.g. do things to keep you warm etc.) changes that are part of thermoregulation
What specific roles does the hypothalamus have on thermoregulation?
- determines the set point (has set point for core temperature - can be changed depending on circumstances - circadian influences etc.)
- receives info about current temp
- decides what to do
How does the hypothalamus know/set the temperature is at set point?
The firing rate of the thermoreceptors (tell you what the temp is) and the set point neurons (what temp you wanna be in) are the same
What happens to core temperature during….
Sleeping
Exercise
- decreases (set point is decreased)
- increases (set point is increased)
Which part of the hypothalamus is active when….
Its cold
Its hot
- posterior (make more heat)
- anterior (lose some heat)
Why do babies have so much adipose tissue?
Adipose tissue is a good insulator. But high surface area compared to their size = losing heat better than adults
What is the role of anaerobic and aerobic metabolism in regulating temperature?
ATP production = heat production
*What are the mechanisms the body uses to generate heat?
ANS (especially via sympathetic)
Endocrine system (thyroxine and epi)
Muscular activity (shivering, increasing voluntary activity)
Non-shivering thermogenesis
What causes shivering?
- Dorsomedial posterior hypothalamus sends axons to the motor neurons and increases their excitation = shiver
- Shivering does not occur by itself, but related to other motions (e.g. breathing). Thus shivering is intermittent
How does the hypothalamus cause voluntary activity for heat production?
Has connections with cortex that sends info down your motor neurons to move
*What are the mechanisms used by non-shivering thermogenesis to produce heat?
Uses hormones like thyroxine and epinephrine to increase metabolic rate = heat production
Increases food intake to increase metabolism
Utilize brown adipose tissue
*How is brown adipose tissue contributing to heat production?
Release of epi/norepi activates the sympathetics (adrenergic) on the brown adipose tissue and hydrolyze ATP
Uncoupling of proteins = hydrolysis of ATP = heat production (very important in infants, also happens in adults in white fat)
What are the two kinds of evaporative heat loss?
Insensible (via the respiratory system, evaporating fluid in the respiratory tract)
Controlled (via sweating, we can still release energy even if the environmental temperature is higher than core)
What is convection?
Conduction?
Heat loss mechanisms.
Convection is when cooler molecules contact the skin/body and carry some of the heat away
Conduction is when physical contact with an object causes the object to take some heat from you
What is radiation?
Heat loss mechanism. Radiation transfers heat between objects not in contact (e.g. you sitting in a room, walls taking some heat from you so you feel cold)
*How can you control heat loss via convection/conduction/radiation?
Controlling the vasculature. If you wanna lose more heat = send a lot of blood to the skin (flushing). If you wanna keep the heat = send less blood to the skin (pale)
Structure of sweat glands
Sweat glands have coiled regions near blood vessels and a duct to transport sweat to the skin surface.
How do sweat glands/sweating work?
Coiled region is innervated by cholinergic neurons that release Ach and bind to the muscarinic receptors on it. Vasodilates the blood vessel around the coiled region causing diffusion of plasma ions (Na, Cl) into the sweat gland. Fluid travels up the duct while Na and Cl is reabsorbed back into the blood. This creates an osmotic gradient as water will follow it back to the bloodstream. The flow of fluid is regulated by how badly you need to sweat.
If I don’t need to sweat a lot…
Low flow rate. Little water is released on the surface and lots more reabsorbed. You release concentrated sweat (high sodium, less water) since you don’t need to lose a lot of water at this time.
If you need to sweat a lot….
High flow rate. Lots of concentrated water released (salty sweat) since you don’t have time and energy to reabsorb since you need to sweat badly
What is acclimation and how does it work?
Adaptation to hot environment. Use aldosterone to reabsorb the sodium (but not the water)
What is fever and how is it produced?
- Change in set point (increased), hypothalamus wants to increase temp.
- Infection produces endotoxins > immune cells are activated and release prostaglandins that increase the set point. Body is trying to keep the heat in and the heat production mechanisms are active (chills when you have fever)
How is fever vanquished?
No more infection = no more endotoxins/prostaglandins = set point returns to normal. Heat loss mechanisms are activated (sweat when the fever breaks)
