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I recently ran into a bio-physical paradox while trying to solve an engineering problem, using nature's way as a guide; namely the brain.

I'm working on designing a totally new system of liquid/gas cooling for a project. In Normal systems, the coolant is first cooled at a point, then sent along to the target areas; however, the coolant gets too hot along the way and cannot meet my target at one of the end components. Additional external cooling fins along the path still do not compensate.

I took biology classes in college and recall some mechanisms of the brain and pictures too (usually depicting the brain as all white internally). So, I theorized that maybe the coolant (blood) was not in direct contact with the brain in a substantial volume; however that was debunked: Why is the brain white?

From what I gather from the major answer, the brain's way of achieving homeostasis might present the answer to my problems. There is a lot of blood in the brain. This blood comes from the carotid arteries, which means it comes from the main circulation, and is hence at body temperature {considering homeostasis of all the body organs i.e. the lungs in this case}. By connotation, the brain should be the hottest organ in the body!

Considering the volume of blood in the brain, how does it regulate its temperature?

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  • $\begingroup$ Great question, thanks for posting it as a new question. +1 $\endgroup$
    – AliceD ♦
    Commented Aug 21, 2015 at 1:21
  • $\begingroup$ Well, blood is highly toxic to the brain, which is why there is a blood brain barrier and there are astrocytes and glial cells that interface between blood vessels and the central nervous system. Homeostasis is maintained chemically much more than mechanically and it is more the task of the glial cells to maintain homeostasis in the CNS. As for heat dissipation, the majority of that happens through the enormous surface area of the skin. Basically the entire body acts as a radiator. And no, core body temperature is 37°C, barring an infection or inflammation. There is no hotter or colder organ. $\endgroup$
    – AMR
    Commented Aug 21, 2015 at 5:42
  • $\begingroup$ What you saw in the post that you linked to is the amount of vasculature that is circulating around the cranium, but that is hardly any different from the amount of vasculature in the rest of the body. Yes the body is able to shunt blood flow to different areas under different conditions using hormones, but the network of blood vessels is still there. If you really want to compare that to a cooling system then calculate the volume and surface area of of all of those blood vessels to the volume and surface area of the brain, then compare that to the cooling components in your project,... $\endgroup$
    – AMR
    Commented Aug 21, 2015 at 5:52
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    $\begingroup$ Amazing! I believe I just got my answer. The chemical cooling you mentioned. All I need is to find an intermediate coolant fluid whose volume at any component along the path will regulate the amount of heat removed along that path before the end component. Though that is easier said than done. Thanks. $\endgroup$
    – haxkalibrr
    Commented Aug 21, 2015 at 12:59
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    $\begingroup$ @AliceD Yes it absolutely is. Just think of the effects the Complement proteins would have if the got anywhere near the tissue of the brain. $\endgroup$
    – AMR
    Commented Aug 21, 2015 at 13:47

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From what I can make up from your question is that you assume the blood in the brain is a bad thing in terms of temperature control. It is not. On the contrary, blood circulation is crucial in maintaining brain temperature.

Under conditions where the brain is heating up, which seems the focus of your question, there are mechanisms in place to extract this heat and dissipate it. Ambient temperature is often lower than body temperature, and even in hot climates, transpiration and water evaporation may cool the skin nonetheless.

Indeed, during hyperthermia, venous blood flow from the skin of the face and scalp fed to the dura mater (the brain's membranes) is enhanced and cools the brain (Brinnel et al., 1989). Moreover, blood from the nasal and paranasal mucous membranes flowing to the dura mater cools the brain due to the evaporative cooling of sweat or mucus. The dura mater may also transmit temperature changes to the cerebrospinal fluid compartment (Zenker & Kubik, 1996).

References
- Brinnel et al., Arch Dermatol Res (1989); 281(1): 66-72
- Zenker & Kubik, Anatomy Embryol (1996); 193(1): 1-13

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