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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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haxkalibrr
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  • Great question, thanks for posting it as a new question. +1 – AliceD Aug 21 '15 at 01:21
  • 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. – AMR Aug 21 '15 at 05:42
  • 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,... – AMR Aug 21 '15 at 05:52
  • ... and if you had a 1000th of the amount of cooling capacity running through your device as compared to the brain, or any part of the body for that matter I would be very surprised... the average human has 96 thousand kilometers of blood vessels in them. Cells are usually never more than 50 micrometers from a blood vessel, and the entire environment is aqueous which dissipates heat much better than air. Either you need to go really cold, N2(l), or you will need better tolerances for the downstream components. Or do like the body does, lots of pipes close together running for short distances. – AMR Aug 21 '15 at 06:08
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    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. – haxkalibrr Aug 21 '15 at 12:59
  • @AMR - blood is highly toxic to the brain? If I would pump demineralized water around it would readily die :) – AliceD Aug 21 '15 at 13:24
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    @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. – AMR Aug 21 '15 at 13:47
  • @AMR - Agreed, it's just that OP's distant knowledge about Bio may make him interpret it as whether blood's a bad thing in the brain. It's not. – AliceD Aug 21 '15 at 13:58
  • @AliceD. Blood flow through highly specialized vessels is not. There are two types of strokes. One is obstructive, the other is hemorrhagic. Both can cause severe disability and both can be fatal. His question says the "(blood) was not in direct contact with the brain in a substantial volume; however that was debunked," but it is not in direct contact. You have extremely tight endothelial cells of the blood vessels of the brain. You have astrocytes that surround the blood vessels and glial cells that protect the neurons. The architecture of the brain has evolved to keep blood out. – AMR Aug 21 '15 at 14:18
  • @AMR oh yes definitely. Blood's kept confined anywhere in the body, only a bit more in the brain via BBB. I am not arguing against, just the tone of the statement. – AliceD Aug 21 '15 at 14:20
  • @AliceD. The use of homeostasis in their question is also problematic, as it is much more than just temperature regulation, but I let it slide. And the BBB is a lot more than a bit more when compared to the rest of the body. It is like the access point to a top secret military installation to the screen door on a porch, or to use an example from Biology, a BSL 3 or 4 facility to a freshman lab. And as far as tone, spend a day on a Neuro ICU and see what they think of blood and brain coming in contact with each other. – AMR Aug 21 '15 at 14:38
  • The gaming sector and data centers have done a lot of work on using liquid cooling. Also if you look at Texas Advanced Computing Center or CERN, they will likely have published plenty of material on component cooling. – AMR Aug 21 '15 at 15:03
  • There is an assumption that the OP is making that is problematic and that is that biological systems and man-made systems operate under the same principals. Man-made systems tend to be run a maximum efficiency or we push the envelop, over-clocking a CPU, afterburners on a jet engines, etc. and we then develop robust cooling systems to try to keep the components at the threshold of failure without exceeding it. Biological systems almost never do this, and metabolic activity is tightly control with enzymes that catalyzes chemical reactions in a controlled manner and with negative-feedback loops. – AMR Aug 21 '15 at 16:20
  • It is only in rare occasions that a biological system pushes the envelop, and that usually has to do with survival mechanisms that are for organism preservation, even if some deleterious effects are endured... Fight or Flight signals, inflammatory response to infection, chasing prey, etc. That is why these things happen in short bursts for short periods of time, because failure in a biological system leads to severe disability or death. – AMR Aug 21 '15 at 16:24

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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

AliceD
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