Metabolism Question

[Some Android]

Quick question about (human) metabolism. I heard that being cold and/or exposing oneself to coldness/cold environments speeds up one's metabolism. I heard this from a source that isn't 100% trust worthy, and I would like some clarification.

Sorry if this is a dumb question.

[5a Violista]

So what I've read is that with decreasing temperature, the metabolic rate at first decreases until a comfortable temperature is reached, then increases again once it's too cold to be comfortable again. According to the chart I saw, the metabolic rate increases for temperatures below 0°C and increases for temperatures above 16°C. Between those two temperatures, however, it's fairly constant and unaffected by temperatures.

It wasn't a primary source, so it may not be completely accurate. I'll have to check its sources to say for sure.

[Dodom]

That's true.

Thermoregulation is controlled by the hypothalamus, which sends signals to the hypophysis, which releases hormones activating the thyroid. Thyronin inhibits cellular respiration: cells have a harder time using oxygen for their energy production, so they do more glycolysis instead, a much less effective way to produce energy that uses up more sugar and leaves the body with more waste heat.
And that's how cold increases base metabolism. (There are more ways to thermoregulate, but the others are autonomic or behavioral, rather than metabolic.)

[Brother Oni]

That's true.

Thermoregulation is controlled by the hypothalamus, which sends signals to the hypophysis, which releases hormones activating the thyroid. Thyronin inhibits cellular respiration: cells have a harder time using oxygen for their energy production, so they do more glycolysis instead, a much less effective way to produce energy that uses up more sugar and leaves the body with more waste heat.
And that's how cold increases base metabolism. (There are more ways to thermoregulate, but the others are autonomic or behavioral, rather than metabolic.)

I was under the impression that lower environmental temperatures increased the basal metabolism through increased thermogenesis.
The main non-exercise based thermogenesis methods are either shivering (which uses ATP) or the proton decoupling of ATP to ADP by brown adipose tissue which releases the energy as heat. Since ATP is most efficiently generated through aerobic respiration, it makes no sense that the body inhibits it (incidentally I'm having trouble working out what thyronin is - did you mean triiodothyronine?).

In humans, glycolysis ends up with various waste products that have to be oxidised, else the rising pH H+ concentration inhibits glycolysis. I'm not aware of any non-disease state mechanism that actively inhibits this oxidation, save insufficient oxygen (please correct me if I'm wrong).

[Dodom]

This is the third time I'm editing this post, this is embarrassing.
You're right about decoupling, what I was told at school was inaccurate on this matter and/or I remembered it wrong. Sorry about my poor vocabulary too, technical terms are really tricky to translate without constant googling (I settle for intermittent googling)

I would however disagree with your last paragraph, the human body does handle glycolysis by-products fairly well (even tough it turns out to be unrelated to the topic), a healthy liver will pick up lactic acid and recycle it, there's some play room before it builds up faster than it can clear.
(I'm assuming the "increasing pH" bit is merely a typo.)

[Brother Oni]

This is the third time I'm editing this post, this is embarrassing.
You're right about decoupling, what I was told at school was inaccurate on this matter and/or I remembered it wrong. Sorry about my poor vocabulary too, technical terms are really tricky to translate without constant googling (I settle for intermittent googling)

I would however disagree with your last paragraph, the human body does handle glycolysis by-products fairly well (even tough it turns out to be unrelated to the topic), a healthy liver will pick up lactic acid and recycle it, there's some play room before it builds up faster than it can clear.
(I'm assuming the "increasing pH" bit is merely a typo.)

No problem - your English is very good and technical talk in any foreign language is difficult to get right. :smallbiggrin:

With regard to my last paragraph, I concede I was thinking solely in terms of heavy exertion in the muscle, rather than a body-wide approach and I definitely agree that under moderate exertion, lactate is picked up effectively.
After heavy exertion though, I would say that the majority of the biochemical regeneration from lactate is done 'on site' in the muscle rather than the liver - it's quicker to get more oxygen to the muscle than to transport the lactate to the liver.

Derp, yes. I meant to put 'rising H+' and I autocorrected H+ to pH. :smallredface:

[Dodom]

Hey thanks by the way. I went to check my textbook to see if there was a textbook error (it happens) versus the teacher misread it versus I misheard the teacher. Anyway now I got this notion corrected thanks to you. Internet culture's confrontational attitude about discussions makes me nervous admitting a mistake but you were nice and helpful, in this day and age it's a thing to appreciate.



After heavy exertion though, I would say that the majority of the biochemical regeneration from lactate is done 'on site' in the muscle rather than the liver - it's quicker to get more oxygen to the muscle than to transport the lactate to the liver.


I only heard of it being cleared in the liver, but that doesn't sound impossible. Do you have more info on that?

[Brother Oni]

Hey thanks by the way. I went to check my textbook to see if there was a textbook error (it happens) versus the teacher misread it versus I misheard the teacher. Anyway now I got this notion corrected thanks to you. Internet culture's confrontational attitude about discussions makes me nervous admitting a mistake but you were nice and helpful, in this day and age it's a thing to appreciate.

No problem. I make it a point to communicate on the internet in the same way I would face to face and that includes giving the other person the benefit of the doubt if you think they're mistaken.

I know enough about science to understand that there's always something that I'm not aware of and as a scientist, I'm always happy to learn new things and be corrected on old ones with updated research. Neither of these are helped by being confrontational and argumentative - the intended outcome is learning, not behaving like Angry German Kid (https://www.youtube.com/watch?v=PbcctWbC8Q0).


I only heard of it being cleared in the liver, but that doesn't sound impossible. Do you have more info on that?

Sure:

Muscle lactate metabolism in recovery from intense exhaustive exercise: impact of light exercise by Bangsbo et al (http://www.ncbi.nlm.nih.gov/pubmed/7836214). They noticed oxygen consumption was increased in the leg muscle specifically after working to failure, indicating that the lactate was being metabolised there rather than being metabolised elsewhere. To double check, they made the volunteers do it with the other leg an hour later. :smallbiggrin:

Lactate Metabolism and Cardiac Muscle by Opie (http://link.springer.com/chapter/10.1007%2F978-3-642-67525-6_2). Textbook chapter, indicating that lactate is an important intermediate energy source in cardiac muscle (cardiac muscle tends to do things slightly differently to skeletal muscle).

Lactate metabolism: a new paradigm for the third millennium by Gladden (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1664920/). This one is a literature review so a bit of a hefty read but is basically 'everything you wanted to know about lactate metabolism but were afraid to ask'.

I can dig up some metabolic pathways if you like, but I think your textbook already has that covered.