A recent online article in Science News https://www.sciencenews.org/blog/science-ticker/red-blood-cells-sense-low-oxygen-brain,  just expands on the fascinating details known about blood and its behaviour.
The article entitled ‘ Red blood cells sense low oxygen in the brain’ is by Laura Sanders published on  August 4, 2016. the first paragraph states that ‘ When the brain runs low on oxygen, red blood cells sense the deficit and hurl themselves through capillaries to deliver their cargo. That reaction, described online August 4 in Neuron, suggests that red blood cells can both detect and remedy low oxygen’

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