What is the mechanism for keeping the testes colder than the body ?
From what I know about refrigeration cooling can be achieved either by adiabatic expansion (like a gas expanding), by evaporation (like rubbing alcohol on your skin) or by chemical dissolution (Sodium Nitrate in Dissolving in water).
So I assume that the body must be using eiher of the above methods. Since expansion does’nt seem feasible here (pun not intended), it has to be either evaporation or dissolution.
Evaporation does’nt seem likely (?) because they testes are mostly covered by underwear (in humans atleast). So does the body make some thing similar to a Concentrated solution of Sodium Nitrate which is diluted near the testes ?
Radiation. The testes are outside the main mass of the body. The extremeties of your body (nose, ears, fingertips) are always cooler than the central mass. Same with the testes.
Wearing tight underwear does cause the testes to stay at a higher temperature than they would otherwise. This is why men with fertility problems who are trying to reproduce are advised not to wear tight pants and underwear.
Radiation ??? :smack: With all due respect, Andrew, Radiation effects are significant only when temperatures are in the range of 1000°C. And for cooled bodies Radiation effects are significant below -50°C (thats why your refrigerator has no shiny lining to reflect it - and pipes carrying liquid ethylene have aluminum foils on them).
** My Question is not about why the testes are outside of the body and why you should’nt wear tight jeans.**
CoderSlave, The temperature of blood is equal or more than the body temperature (mammals are warm blooded). So more blood flowing through the testes will make them warmer ! not cooler.
Transfer of heat doesn’t require “refrigeration.”
Don’t forget the basics: conduction, radiation, and convection. By dangling the goodies away from the body, transfer of heat from the body by conduction is reduced while (depending on the undergarment) increasing convection and radiation through increased surface area. Evaporation on hot days may also help.
You shouldn’t insult someone who’s just given you a correct answer, kiddo. The body radiates heat (this can easily be seen on infra-red). And the dangly bits don’t need to be 1000 degrees, either. Posterchild has answered the question nicely.
Qadgop the Mercotan - I did’nt insult anyone, infact i was more respectful.
Everything (which is above 0K) radiates heat. But it is not significant to cool down things at ambient temperatures in reasonable amount of time.
And merely dangling it away from the body, reduces heat transfer from the body, but for anything to cool down below ambient temperature u’ll need either evaporation or a colder souce.
I’d appreciate if someone can give some cites on this.
There are many situations where radiative cooling makes a big difference even at room temperature or below. On a clear night, frost may form on the ground due to radiative cooling even when the air is several degrees above freezing. The inside surface of a thermos bottle (i.e. the two surfaces of the vacuum cavity) is coated with metal (aluminum, I think) because otherwise, radiative transfer will ruin the insulation.
However in case of the testicles, conduction/convection is the major method of cooling. Especially when wearing pants. (Conduction and convection are basically the same thing - it’s heat transfer by contact. If it’s in contact with moving fluid it’s convection, if it’s stationary fluid or solid it’s conduction.)
The testicles don’t need to be at room temperature. They just need to be a couple of degrees below body temperature. By dangling them outside the body (so to speak) the surface area is increased, and temperature is lowered just enough. On cold days they retract closer to the body to make sure they don’t get too cool.
There are various things animals do to control temperature, but an endothermic chemical reaction is not one of them.
Also, let’s not forget that there’s plenty of evaporation going on, too. Ball sweat is an every day thing. Take a reach down there and see if things aren’t a bit moist.
But yeah, the boys aren’t at “ambient temperature” most of the time, at least mine aren’t. If I had to guess, I’d say they were at 94 or so right now, while the room is at closer to 70. If my testes were 70 degrees, I sure as hell wouldn’t be posting here.
Evaporative cooling is the main form of cooling in the human body. The hypothalmus has the control mechanism to control the temperature and also the key temperature sensors. Sweating begins almost precisely at a skin temperature of 37°C and increases rapidly as the skin temperature rises above this value.
If the skin temperature drops below 37°C a variety of responses are initiated to conserve the heat in the body : Vasoconstriction,
stopped sweating, Shivering to increase heat production in the muscles, Secretion of norepinephrine, epinephrine, and thyroxine to increase heat production, etc.
I can understand the obvious conduction, convection and radiation heat transfer. But does the hypothalmus have a special control mechanism for the testes ?? I appreciate all your help, but, I need Cites to back up all your claims.
The testicles and scotum have special muscles, the cremaster and the tunica dartos, that control their position and surface area in response to temperature. They also have a special network of blood vessels called the pampiniform plexus that act as a countercurrent heat exchanger (where arteries lose heat to veins) to cool the blood going into the testicles. (You guys can argue about whether this constitutes radiative cooling or not, but it seems to me that cooling something by varying the ratio of surface area to volume has to be radiative.)
Somewhere in your nervous system is a place where temperature information from your testicles is processed, and a decision is made to raise and lower them via the cremaster and/or spread them out or contract them via the tunica dartos to adjust the temperature. There may also be changes in the diameter of arteries/veins in the pampiniform plexus. I don’t know if that decision is made in the hypothalamus or not, since it seems like a simple reflex that isn’t tied to the rest of the body’s temperature.
Thanks Bob Scene. That was a great answer. The countercurrent heat transfer between blood from arteries and blood from viens make sense. But even using countercurrent heat transfer, the lowest temperature the testes could get is the temperature of the inlet blood in the arteries. So, I assume the arterial blood temperature is indeed below body temperature (?) Can you please confirm that ?
No, the blood in the arteries in this case starts out warmer than the venous blood because it’s been inside the abdomen. The blood in the veins is returning to the body from the testicles, and it’s a little cooler than the arterial blood because it’s been outside the abdomen. The heat exchanger lets some of the heat from the arterial blood pass to the venous blood so that the testicles are getting cooler blood than they would if it came straight from the abdomen.
Venous blood cools off when it circulates through parts of the body closer to the outside where it’s cooler - you radiated off body heat which cools blood in those areas more. Your internal body temperature is different than your skin temperature; I’m sitting here holding a thermometer in my hand for the past 5 minutes and it reads 34.5C… that ain’t the temp inside me though.
Check the temp of your hands, nose, ears, face… well anything next time you’re out throwing snowballs or in the cold - those peices of you still have blood flowing through them but it’s no longer at 37C.
The venous blood is colder because it’s been flowing through the testicles, which are already at a lower temperature than the abdomen. All of the mechanisms your body has to shed heat are surface-based, of course, and your testicles have much more surface area per volume than your abdomen, so they normally stay cooler, even without extra mechanisms like the heat exchanger.