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There is lots of information online about the circulatory system, but it never seems to answer the question of "targeting".

When there is a change in the relative demand for blood, how does the circulatory system direct scarce resources to the right place? Is it mediated by the nervous system or some other mechanism?

  • Well, it’s a mixture of first come first serve and nervous regulation. The two main antagonists of the vegetative nervous system, Symphatikus and Parasympathikus do a so-called vasoconstriction: They simply close arteries that go to body parts which are currently deemed not needed. In case of fight or flight, the Symphatikus will dilate the arteries of the lung and heart, increasing the blood volume available to the body and shutting down the digestive system. // I think your question would strongly benefit if you could include how large your background knowledge is, and your prior research. – Narusan Dec 19 '18 at 22:46
  • I also think the question would be improved by removing the words oxygen and nutrients. The body can regulate blood flow to various parts of the body, but that blood contains the same stuff all the blood in the rest of the body contains. There is no selective delivery of oxygen, glucose or anything else contained in blood. – Carey Gregory Dec 20 '18 at 15:45
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The easiest explanation is that there is no "knowledge" involved, just physiology/molecular biology. In an area of low O2 and high CO2 (therefore a demand exists for O2), the oxygen dissociation curve will favor O2 release into the blood, which will then oxygenate the tissue.

Similarly, concentration of CO2 affects localizes extravascular pH. If there is a high amount of CO2 - which occurs with muscle use, among other things - the change in pH caused dilation of arterioles, allowing more blood to flow to those tissues that need it, releasing oxygen via the O2 dissociation behavior.

This is a simplified but essentially correct of the control of oxygen release to tissues that need it.

But the greatest subsequent vasodilation [in skeletal muscle] is due to local chemical factors. These are changes that occur during exercise in the extracellular fluid surrounding skeletal muscle cells. Such changes occur naturally as the cells consume more energy; in other words, the effect occurs automatically as a muscle exercises and only in the specific muscles working. The brain does not need to get involved in trying to adjust blood flow to the correct muscles. It happens automatically through this local mechanism.

More information can be obtained by reading the article linked to below.

Control of Arterioles

  • This is a simplified but essentially correct [model/explanation] of the control of oxygen release to tissues that need it. I think there‘s still something missing. The typos I would have been able to correct as well, but I‘m not sure what you wanted to fill the gap with. No worries ^^ – Narusan Dec 21 '18 at 15:07

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