Vasodilation occurs when it is hot

[biophysics]

I understand that vasodilation occurs when it is hot (to evolve heat away) and vasoconstriction when its cold (to retain heat)

1) What is the mechanism through which heat causes vasodilation?

2) How hot is our blood (temperature). Is it hotter than 98.2 F because of glycolysis?

Thanks

 

[jim mcnamara]

Hmm maybe this should be in the homework section.

1 - the body's thermoregulation (homeostasis is the topic you'd start with) system dilates
"local" blood vessels near the skin when the body's core temperture rises due to high ambient temperature, exercise, or sometimes illness. The trigger is the level of intracellular calcium and phosphorylation of mysosin (MLC mysosin light chain molecule).

2. Your core temperature (the warmest blood) varies in a diurnal rhythm and across individuals and physical exertion levels and age. Withe regard to age: Brand new newborn infants do not thermoregulate the way us big people do. You have to keep them warm and dry for several hours, and not let peripeheral blood temps go below guidelines. For example, nurses will defer bathing until the baby's axillary temperature is stable and above 36.4 deg C, and keep the baby's head covered with a cap minimally for the first twelve hours.

Peripheral blood tempatures can vary even more due to environmental factors.

Temperature readings on one person measured at the same time at different places also vary. Temperature (the 98.6 deg F you probably know as "normal", or oral temperature) will be slightly higher when taken rectally or taken from the tympanic membrane - about 0.5 deg F to 1.0 deg F higher. Axillary temp (armpit) will be lower.

So there isn't a one 'temperature'. And I don't think glycolysis per se is a massive contributor, because I've read that consumption of oxygen correlates well with core temperature readings - the basic metabolic rate - and glycolysis is anaerobic.

One digression - there is a hypothesis that one contributor to obesity in developed nations is central AC and heat. Because the body does not spend a lot of extra calories cooling off or staying warm. You decide if you like this idea. I find it interesting.

 

[biophysics]

thanks for your reply, very interesting

I've heard that fermentive cells produce more heat than those cells which use aerobic respiration.

I understand that fermentation produces 2ATP/glucose while aerobic respiration produces about 30ATP/glucose.

Thus more energy is given off as heat in fermentation, but what is the mechanism for how heat is produced here?

How does temperature affect Calcium/MLCK?

 

[biophysics]

Any ideas will be appreciated

My question: I understand how friction produces heat. How does a biological process like cellular respiration produce heat?

 

[jim mcnamara]

It is chemically produced heat - a tiny bit like like oxidizing paper in a flame -
slowly.

Mitochondria at work:

Some of the energy released by electron transport does no useful work at all (that law of thermodynamics is at work again). That is, each exchange of electrons results in a loss of some energy as heat.

Also, dissipation of the chemiosmotic gradient without doing work results in the transformation of more energy to heat. Respiratory control can be 'exploited' to increase heat production by dissipating the gradient at a faster rate, or to slow heat production by making the ETS more efficient. This kind of regulation is effected by the hormone thyroxine - the thyroid hormone.

 

[biophysics]

thanks, that make sense: The redox reactions of metabolism are exothermic and use some of the heat released to establish a proton gradient while the rest is released as heat.
My next question:

How can heat (exothermicity) be used to do useful work?

I know you said that glycolysis isn't a big predictor of heat. However RBCs don't have mitochondria and use fermentation only. This is causes a lot of heat. Any ideas why?