Comments
SirDuke6 OP t1_j29kxgp wrote
Sometimes the transfer of heat almost seems instantaneous, is that really how fast the blood travels through the body on a regular basis?
ThePhoenixBird2022 t1_j29njw6 wrote
If you look at your foot, you can see more veins near the surface of the skin than you would if you look at your lower leg because there is far less fat or muscle. With all those blood vessels near the surface of the skin to help transfer heat/cool between the blood and skin surface, feet are great temperature regulators.
Akward_Tortoise t1_j29oquk wrote
It's instant because of the temperature difference between under the covers she outside the covers. You haven't lost a whole lot of heat, but you can feel the temperature difference in your foot immediately.
SirDuke6 OP t1_j29p22z wrote
Sorry, I should've been more descriptive. I meant an instantaneous change in parts under the blanket still. Not the foot out of the sheet.
I'm pretty dumb but I'm not THAT dumb lol.
SirDuke6 OP t1_j29p7tt wrote
So would it be pretty much anywhere that has blood vessels close to the skin? Pretty much anywhere that doesnt have much fat/muscle underneath the skin?
macedonianmoper t1_j29qsl7 wrote
Keep in mind that if you have one foot out the blankets are most likely not perfectly closed so air from outside can come in so it's not just the cooler blood circulating in your veins, it's also that the moment you put your foot outside the entire air below the blankets also cooled
KnitYourOwnSpaceship t1_j29r6jk wrote
I've sondered the same, and my theory is that you're also disturbing the air under the blanket when you move your foot. Sticking part of yourself outside the blanket gives the chance for colder air from the room to move under the blanket. It's not a complete change of all the trapped air, but enough to make a difference pretty quickly.
Veritas3333 t1_j29xitj wrote
Also, it's called a radiator foot!
AsoHYPO t1_j29y1ih wrote
Do you mean a feeling of instant relief like how you instantly feel less thirsty after drinking some water despite it needing a little while to enter your bloodstream?
[deleted] t1_j2a15sl wrote
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jerpha t1_j2a1qhd wrote
It is about the flux. If you are storing heat, you will feel hot. If you are loosing heat, you will feel cold. Temperatures almost don't matter.
Take a steaming hot shower, when you're done get away from it, you will feel cold even though your place is ar room temperature. You're actually loosing some heat.
Take a very cold shower, you will feel hot because you're storing it.
If you're close to not loosing neither storing, you will just feel neat.
Putting your foot outside the blanket just makes you store less heat. Plus yes feet have a lot of blood flows that helps the thing.
SirDuke6 OP t1_j2a3u8g wrote
Kind of but more of a physical feeling in other parts of the body like the other leg or torso being cooler as opposed to a psychological feeling of being less thirsty.
SirDuke6 OP t1_j2a3y4a wrote
Makes sense, especially because if you were to lift your leg at all, the blanket rising would create a vaccuum that sucks in colder air.
nstickels t1_j2a53d3 wrote
Blood moves at roughly 3 feet per second through the body. So assuming average height, it’s approximately 1.5 seconds for blood from the foot to go back to the heart, where it is pumped out again throughout the body. This is repeated every single beat your heart is making. Now that cooled blood will be mixing with warmer blood in the heart, but each and every beat after that first 1.5 seconds will be mixing in slightly cooled blood from your foot over and over.
SirDuke6 OP t1_j2a70yg wrote
That's awesome. I had no idea how fast blood moved but that's pretty incredible.
I mean, I know how powerful it was based off of things like how far blood squirts out of an artery/vein when cut but didn't have an actual speed to comprehend it at.
Nyaos t1_j2abntf wrote
That’s interesting. I probably have under appreciated how much sandals can help keep you cool.
biff64gc t1_j2aj08v wrote
While a round trip can take nearly a minute, your foot is at one extreme. It's only path available is back towards your core so it does happen within a couple of seconds.
The effect happens similar to a coolant line with a radiator. Your foot expels a lot of heat quickly because of the temperature difference, cooling the blood off. That now cool blood travels back up to your core, immediately absorbing heat from your much warmer core area. So what happens to your foot, the reverse happens in your core with the same blood.
The greater the difference in temp at your foot, the faster it expels heat, the cooler the blood, the faster it absorbs heat from your core once it gets back up there.
So you don't need to wait for the blood in your core to reach your foot to feel cooler. You just need cooler blood to enter your core.
ImReverse_Giraffe t1_j2akyis wrote
Yes. If you're ever really hot, run cold water on the inside of your wrists. Those veins are near the surface and lead directly to your heart. It'll cool you down so fast it's crazy.
ImReverse_Giraffe t1_j2al66t wrote
It's a psychological effect. Just like the drinking water provides "immediate" relief even though it really doesn't. It's your brain rewarding itself for doing something it decided it needed to do to survive. The brain is funny like that.
SirDuke6 OP t1_j2ano69 wrote
Life pro tip for free? Thank you!
SpectralMagic t1_j2auzzn wrote
The soles of your feet have plenty of blood circulating through them, this combined with our feet's double-water pores and increased amount of pores per cm^2 makes it easier to shed heat through perspiration. Water is incredibly good at temperature regulation because of the energy required to heat and cool it to different states
Our palms and soles have an increased amount of sweat glands to provide greater friction with surfaces, our soles with ~600-700 pores per cm^2.
Edit: can't find a source for the "double water sweat glands", but I recall seeing something about it in a PBS documentary comparing humans to other primates, more specifically how sweating more efficiently may have given us the evolutionary advantage
abat6294 t1_j2avb17 wrote
People talking about heat transfer at your foot, but I think the bigger affect is how when you stick your foot out, you've created an opening in the blanket that allows warm out to leave and for cooler air to enter.
iNd3xed t1_j2avjsv wrote
Although the above comment is not wrong about the high speed of blood this is only the case close to the heart.
In smaller blood vessels, and especially in veins, blood flows much slower, as low as a couple of centimeters per second in the index finger [https://pubmed.ncbi.nlm.nih.gov/11284002/]
Not that this helps answer the original question by much, but this adds some nuance to the answer
fiendishrabbit t1_j2ay0ih wrote
If I remember my biology right, on average it takes 45 seconds for blood to make a full round-trip. Very fast in the aorta, much slower elsewhere.
cherrybounce t1_j2ayzsz wrote
The feet are ideally suited to helping us keep a stable body temperature, for a few reasons.
They - like the hands - have a large surface area as well as specialised blood vessels which can be opened up to pass high volumes of blood through them and therefore offload heat quickly when required.
When not required, the blood vessels are constricted.
This, coupled with the fact that the feet (and hands) are at the end of our limbs and don't have much muscle (which produces heat) means that they cool down much more than other regions of the body.
BuildANavy t1_j2b2fzb wrote
100% this. Heat transfer from the foot itself is definitely a factor, but I don't think it's the biggest one. While by no means sealed, the air within the blanket becomes pretty stagnant and holds heat while you're underneath it. When you stick your foot out you are creating a significant opening as well as air currents and turbulence from the movement that allows a large exchange of warm air under the blanket with cold air from the room.
You can easily test this by very gently poking your foot out of the covers while keeping them tightly wrapped around your ankle. You don't get the same cooling effect (I just tried it while I was writing this).
P.s. if I'm hot in bed I just kick my leg up high, which lifts the covers and lets all the warm air out/cold air in. Don't need to leave my foot stuck out to be quickly cooled down.
BuildANavy t1_j2b32fa wrote
Not really. When you get out of a hot shower and move into another room you feel cold because there's a lot of water evaporating off your skin, taking latent heat with it. Also, if you have ever been very cold you will know that just sitting in front of a fire doesn't immediately make you feel warm; even though you are warming up straight away it takes time for you to feel warm.
quitegonegenie t1_j2b39hl wrote
To quote Moby-Dick:
"We felt very nice and snug, the more so since it was so chilly out of doors; indeed out of bed-clothes too, seeing that there was no fire in the room. The more so, I say, because truly to enjoy bodily warmth, some small part of you must be cold, for there is no quality in this world that is not what it is merely by contrast. Nothing exists in itself."
Fat_Doinks408 t1_j2b45zj wrote
3ft per second?! Thats a lil hard to belive, ima have to look that one up.
d4nowar t1_j2bqmbb wrote
You've seen the squirting blood trope in movies, right?
[deleted] t1_j2byma9 wrote
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lazerdab t1_j2bz9m8 wrote
Most of the skin on you're body fluctuates how much blood is near the surface to regulate temperature. The bottom of your feet doesn't do that so much so blood stays relatively close the the skin surface so your feet are great out sending out heat.
Fat_Doinks408 t1_j2c2j8o wrote
Yeah ive also seen exploding cars in movies.
[deleted] t1_j2c8dbq wrote
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rusty-lewis t1_j2c8tvz wrote
Your blood makes a complete circulation three times every minute. This includes your extremities. I have always attributed the instant cool feeling to this fact coupled with the blood vessels close to the surface. It’s also the reason you can cool down really quickly by putting you hands in cold water in the summer time.
Scoobysmith44 t1_j2c9jv1 wrote
Just to piggy-back, basic first aid to quickly cool someone suffering from heat stress/exhaustion, use ice packs or cold, wet towels on the head, neck, groin, trunk and under armpits.
More info from OSHA
FcBe88 t1_j2cagkk wrote
What a wonderful excerpt of the human experience of sticking your foot out of the bed when it’s cold.
Taverdi84 t1_j2cb2ia wrote
What I THINK you may be referring to is an inner-thermostat connected to your nervous system event. The sensation of relief from temperature change has a lot to do with the mind and expectations. A good little experiment is to hold one hand onto a cool surface (wooden table works best) hold that one hand there for about 20-30 seconds. Then switch hands in that exact same spot. The spot where your first hand felt cool on the table the whole time will now feel warm to the other hand. This is especially sensitive with hands and feet because they’re like little probes for the world around you.
[deleted] t1_j2ce0yw wrote
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[deleted] t1_j2ce3u7 wrote
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cbeck23 t1_j2cpie2 wrote
Correct. That is why when it is hot , I put rubbing alcohol on the tops of my feet, sides of my neck, and back/inside of my knees
Inphearian t1_j2cr07q wrote
Well what are the results.
DonutCola t1_j2cur1m wrote
That’s silly dude there is no fan circulating air out of your blanket besides your asshole
DonutCola t1_j2cuszs wrote
How tf does cooler air magically enter? You’re not really creating a viable convection current dude. It’s just like a brain illusion thing.
Fat_Doinks408 t1_j2cwad8 wrote
Hes right! Lol
tempusfudgeit t1_j2cwadl wrote
Tell me you've never been camping and slept in a sleeping bag
LandoChronus t1_j2cwcga wrote
Ok, I threw some icepacks in the back of their car, now what?
DonutCola t1_j2cwhrd wrote
That’s radiant heat
[deleted] t1_j2cyoh9 wrote
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sheevum t1_j2d18gq wrote
This is the right answer. It’s not just about draining heat, but the key is that they can drain and regulate temperature very effectively. So sticking one foot out is enough to regulate your temperature, which it can’t do effectively when your whole body is hot. It’s an adaptive radiator when stuck out.
CanISellYouABridge t1_j2d1oo8 wrote
Well you warmed the table up by pressing your palm into it for 20-30 seconds, of course the spot will feel warm to your other hand.
jpwanabe t1_j2d53it wrote
Holy shit. Did not know it moved that fast
wee-g-19 t1_j2d58cf wrote
I enjoy doing this it feels good. I work outside so most times wrap up warm, when overheating I pull my beanie up over my ears and I start to cool down without removing layers. Still warm I then roll up sleeves. Do whatever before removing a layer.
Adonis0 t1_j2d59br wrote
It’s perception
Your brain goes, I’m too hot right now but that will be fixed in a few moments so we’re going to make it feel fixed now so we don’t go overboard
If you only felt comfortable when everything was right you’d be stuck in a yo-yo of toss blankets off, get too cold, rug up, get too hot. So your brain makes it feel fine when you’ve done enough to fix it
Adonis0 t1_j2d5c8a wrote
Also, your foot is the furthest from your heart, and so cooling there helps it radiate a lot of heat from the body as in the return trip it cools your leg and torso a little
Tobirama4374 t1_j2d6vta wrote
Coz they are literal heat sink. Think of hairless skin patches on body like foot soles, palms and facial area that don't grow hair as heat sinks in machine that need to throw away extra heat. Body is never not burning calories and thus constantly creates heat which is also why balls are outside so sperm don't die of heat.
courageous_salmon t1_j2d82op wrote
Forget the scientific explanations, it’s about tension and release. It’s the same reason a foot outside of the covers going back in also feels great.
jolloholoday t1_j2dggsx wrote
Just tried this, now my bed is soaked. Thanks for nothing.
Spiritual_Worker3062 t1_j2dhfq9 wrote
Because blanket provides a kind of safety and the leg controls the temperature, so you feel safe and comfortable.
Blankets are warm, soft, cover(“protect”) you. By being under a blanket you feel safety, comfort. And it separates you from the outside world, making it easier to fall asleep. But despite all the positive effects of being under a blanket, temperature can’t be controlled.
MalleableCurmudgeon t1_j2dhns2 wrote
I served in Iraq during the ‘00’s and on particularly hot days, after patrols and convoys, we’d go to the medics for a bag of IV fluid they’d keep slightly chilled. Holy holy! The relief of cool fluid directly into the veins and feeling it move from my arm throughout my whole body was awesome!
royalsilk t1_j2dnabx wrote
3 main heat dump locations on your body, your palms, your upper cheeks and forehead, and your bottoms of your feet. Combine that with venting an already hot and contained area and you get immediate relief.
4tehlulzez t1_j2dp6m3 wrote
Now put them basically everywhere besides the feet like the commenter said.
[deleted] t1_j2dpjcq wrote
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abat6294 t1_j2dviq9 wrote
It doesn't rush in, but now there is an interface where cold/warm air can exchange. Having 1 small opening for air to flow is significantly different than having 0.
tryinadosomethingher t1_j2dwddw wrote
Don’t need a fan.. do you o own what happens when hot and cold air touch? When a cold front hits a hot front? It’s creates rapid air movement :) this can be felt when opening a bathroom door after a hot shower
tryinadosomethingher t1_j2dwugh wrote
Heat rises. When hot air from the blanket open and touch the cold air.. we’ll you know what happens when a cold and a hot front meet. Ever open the door after a steamy shower and see the air move fast? Same principle with the hot air under your blanket just not as drastic
DonkeySilver6051 t1_j2dysvv wrote
But isn't that very fleeting? Or is it enough to cool down? Apologies for my ignorance.
DonkeySilver6051 t1_j2dzwey wrote
This begs the question though, if said live sperm enters the female body it must be extremely hot in the uterus area during eg a heat wave. Just wondering.
Conflucius t1_j2e4zjs wrote
It said on, not in. Quit being weird and strap them to a tree like the rest of us.
bkydx t1_j2e5yqb wrote
Glabrous skin is located in 3 parts of your body, the sole of the foot, palms of your hands and forehead.
It lacks the hair and pigmentation and has extra pores for heat transfer.
The skin on the rest of your body is thick and well insulated and designed to keep heat in and everything else out.
borg286 t1_j2e6cvc wrote
Where is this trunk on a person? Honest question.
bkydx t1_j2e6ucd wrote
Palms and feet and forehead all work better.
Glabrous skin is designed for heat transfer and only located in these 3 spots.
The skin on your wrist does not transfer cold as effectively beneath the skin surface.
Other suggested locations are Neck/arm pits because they are thinner cutaneous skin similar to wrist but the blood flow is direct to your brain.
De-oxyginated blood from your wrist goes to your heart and not your brain and there would be little cooling effect and less benefit then using any of the medically recommended cooling areas.
bkydx t1_j2e6wvh wrote
Except its wrong.
bkydx t1_j2e7pse wrote
Incorrect.
Soles and palms are made of glaborous skin design to let heat out.
Cutaneous skin keeps heat in.
A fan or creating airflow is airflow has absolutely nothing to do with biology.
bkydx t1_j2e845c wrote
No.
You have 2 types of skin.
Cutaneous - Thick, harry, pigmented, less pores, Doesn't transfer heat in or out of your body well.
Glabrous skin - Hairless, pigment less, Lots of pores. Transfers heat well.
​
Glabrous skin is located on your palms/soles and forehead.
bkydx t1_j2e8bul wrote
Glabrous skin vs cutaneous skin.
bkydx t1_j2e8mxy wrote
It's biology
Cutaneous skin is bad at heat transfer.
Glabrous skin is good at heat transfer.
Any other explanation is wrong.
bkydx t1_j2e97by wrote
Science has the exact unarguable answer but lets just ignore it and be idiots.
Glabrous skin is good at transferring heat.
Cutaneous skin is bad at transferring heat.
peanutbutterwife t1_j2eamoj wrote
The chest and abdomen. Everything that isn't your head and limbs.
cbeck23 t1_j2elr1n wrote
When it is that hot, any relief, however fleeting, is appreciated. Alcohol will flash off, but takes some of your body heat with it. It is enough to help if you are having problems falling asleep, and if you're awake, slather on some more Alcohol when it dries.
Crepuscular_Oreo t1_j2fdd4p wrote
>I had no idea how fast blood moved but that's pretty incredible.
The speeds of various bodily processes are interesting. I have nerve damage. I was lying on the table at the doctor's office while they were testing the speed that signals travel from one part of my body to another. Being bored while the tests were going on, I did the math and calculated that the runners in the 100-meter dash at the Olympics run faster than my nerves send signals through my body. That seemed strange to me; I always thought of nerve signals being instant. It was several years ago so I don't remember the exact numbers.
krammark12 t1_j29k2q2 wrote
The veins in your foot are relatively close to the surface, making heat transfer from your inner body to the outside temperature much easier. The blanket (or socks) are isolating your feet, making this transfer more difficult.