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Name: Drew H
Status: student
Age: 10
Location: N/A
Country: N/A
Date: 8/26/2004


Question:
When bats sleep upside down does all their blood rush to their heads like when people are hanging upside down?


Replies:
Bats are so small that, unlike humans, the problem of blood distribution is not a huge problem. They are able to wrap themselves into a small package and like most mammals, they can regulate blood flow by contracting their blood vessels to direct and achieve blood flow.

Steve Sample

Up-dated July 2008
I concur with the other answer here. I had noticed several sources on the internet that describe "special valves" that keep blood from pooling in the head (I was studying to co-lead a presentation on bats), however none of my bat books describe this. In fact, the book "Flying Foxes" by Leslie Hall (2001) states: "It was once thought that bats had a series of valves in their blood vessels which prevented blood rushing to their heads when they were upside down. No such valves have been found and it is considered that bat's small size and the small amount of blood allow them to sleep upside-down." I would consider the valves a myth until shown otherwise.

The internet claims usually mention that similar valves in human veins prevent blood from pooling up in our legs, however this mechanism relies on fairly regular movement to "squish" the blood past the valves (which explains the discomfort of standing motionless for a few minutes), and they are not important during the relative motionlessness of sleep, since we sleep laying down. So in summary, the relatively small size of bats (and many similar sized animals in the insect world that can rest upside down) is probably the prime reason.

Paul Bridges


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