2
$\begingroup$

Background information:

According to chemistry-reference.com, there's a chemical reaction that uses up a mole of ammonium chloride/sal ammoniac, a mole of lye/sodium hydroxide, and 30.56 kilojoules of energy to produce a mole of water, a mole of salt/sodium chloride, and a mole of ammonia. In other words, I only need a single mole each of lye and ammonium chloride to cool more than a minute's worth of pumped blood by 1 degree Celsius - as a matter of fact, we can probably cool the blood as much as we want, since the reaction really doesn't need much of this stuff in order to function - the primary problem is venting the ammonia waste product.

A creature I'm working on takes advantage of this. Right before its blood vessels feed into its heart, a web of them - a rete mirabile, or, in technical terms, a cooling jacket - wraps around a biological chemical reactor within the creature's body, which is where this reaction occurs. When physically exerting itself, it triggers a valve in that chamber (a la a bombardier beetle's chemical-mixing mechanism), carries out the above chemical reaction, vents the resultant ammonia - which it can regenerate later - to the atmosphere, stores the salt in some kind of special receptacle, and pees the water out later. In exchange, the creature's blood gets heat sucked out of it, thereby reducing the rate at which it overheats.

The question: how cold can this creature make its own blood before said blood stops working? After all, as I said above, the blood can be cooled as much as I want; the unknown variable here is how much it can be cooled before bad stuff starts happening.

I recognize that the viscosity of blood increases as its temperature decreases, meaning that low-temperature blood is harder to pump, but that's not really the problem here since, after getting the heat pulled out of it, the blood will rapidly begin picking up more heat and its temperature will increase again. However, is there a temperature at which red blood cells can no longer carry oxygen, or at which they freeze so much that they can't function again - i.e. where it doesn't matter how much they get re-heated, because the sudden drop in temperature irreparably destroyed them? I'm currently thinking that that's somewhere between "freezing" and "normal body temperatures".

Don't worry about anything else related to this creature's rather unique biology - i.e. how it produces/stores ammonium chloride and lye or vents ammonia. That's not what this question is about. Moreover, this creature is, for all other aspects - including the makeup of and chemical structure of its blood - a relatively normal human being.

Inspired by Gilgamesh's answer to this question of mine.

$\endgroup$
14
  • 2
    $\begingroup$ I tried Google on "temperature hemoglobin". Lowest experimental temperature on life laboratory animals I can find for hemoglobine/oxigen functionality is 13.7 degrees Celcius. A rise of temperature from this hypotheric condition may be problematic, so the temperature is preferred to remain constant, not variable. The source may be interesting for you, I don't have the expertise for a good interpretation, so this is no answer, only a link frontiersin.org/articles/10.3389/fmed.2021.808025/full $\endgroup$
    – Goodies
    May 9 at 21:00
  • $\begingroup$ @Goodies Thanks - reading through that now. $\endgroup$
    – KEY_ABRADE
    May 9 at 21:04
  • 1
    $\begingroup$ @LoganR.Kearsley This chemical equation produces about 22.4 liters of ammonia at STP; even if it occurs over the course of a minute, that's about 1/3 of a liter per second. For reference, a human's lungs can hold about 6 liters of air at STP. Unless this critter can turn a mole of ammonia into a significantly less dense and therefore storable form within seconds, it's going to have to vent it. If you do have such a mechanism for it to do so, please let me know, because I've considered everything from converting it to urea to converting it to carbamate to converting it to ammonia water. $\endgroup$
    – KEY_ABRADE
    May 9 at 21:36
  • 2
    $\begingroup$ @Daron Reacting a mole of lye, a mole of sal ammoniac, and 30.56 kilojoules of energy outputs 1 mole of ammonia gas, 1 mole of liquid water, and 1 mole of solid salt. At standard temperature and pressure (en.wikipedia.org/wiki/Standard_temperature_and_pressure), 1 mole of ammonia takes up 22.4 liters of space. If the reaction happens over the course of a minute, it outputs 22.4 liters/60 seconds = about 1/3 of a liter per second. $\endgroup$
    – KEY_ABRADE
    May 9 at 23:16
  • 1
    $\begingroup$ If your goal is to offset overheating (presumably from muscular exertion), then it's much more practical to draw the cooling process out by controlling the rate of your endothermic reaction - you suck out the same amount of heat/energy, but over a longer time, meaning your blood never goes cold enough to impair functionality and you can control the timing of the cooling effect more precisely and you have time to vent some waste products and I suspect the reaction is more efficient. $\endgroup$
    – Ottie
    May 10 at 12:12

2 Answers 2

4
$\begingroup$

Ten Celsius

enter image description here

Lizards are cold blooded and can survive as low as 10C. For comparison a pitiful human will simply stop working if the internal temperature goes outside the 35C - 40C range for too long.

The lizard is not happy at this low temperature. In fact it can barely move. But its blood certainly still works as blood, evidenced by how the animal is not dead.

Your creature can survive at 10C if you make it more lizardy.

$\endgroup$
3
$\begingroup$

Within a degree of absolute zero.

There are many species of fish that survive in the sea below 0 C, the normal freezing point of water. Frogs and turtles can freeze solid during the winter. With the right antifreeze proteins, or other tricks like glycerol or trehalose, you humans' blood could be comparably resistant. See this paper for human blood cooled to below 1 K with less than 1% hemolysis.

Freezing blood entirely, of course, interferes with respiration and related activities. But many biological samples are kept liquid in glycerol at -80 degrees C. Glycerol would be viscous, but I doubt your organism is moving too fast at those temperatures anyway.

$\endgroup$
2
  • $\begingroup$ Would it keep working to transport oxigen via hemoglobine, or is the substance just preserved, kept intact ? This opening is about a life, functioning and moving animal. $\endgroup$
    – Goodies
    May 9 at 21:51
  • $\begingroup$ Chilled blood can be subject to special difficulties, and almost any blood will have slower gas diffusion in the cold. But so long as it can be maintained liquid, some oxygen should be transportable by it. The question suggests freezing and reheating is also allowable, and indicates the creature can reheat itself by some means. $\endgroup$ May 9 at 22:31

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .