system
Given the following post, respond as if you're commenting on Reddit:
human
How are bats able to hang upside down for extended periods of time without the side effects of blood rushing to the brain?
gpt
Essentially, bats and mammals in general have really tough and intelligent blood vessels. they're rubbery and they're lined with muscle that can actively close off unnecessary blood supply and control blood pressure separately in different areas.  what's more is that we have one-way valves that prevent the load of blood from traveling backwards. A healthy organism has a very resilient blood vessel system that constantly regenerates, stays springy, and can even thicken with an increased load (the latter is sometimes not desirable)

A bat is.. about 0.5oz. the pressure difference is going to be on the order of grams. Their tissues however are made of the same things that ours are. That's a far better strength-to-weight ratio compared to 12 pounds of blood (approx 384 bats) circulating through our body

Let's ask a contrary question. How are we able to stand for extended periods of time with no problems? Same deal. Strong and muscular blood vessels can restrict blood pressure in select areas so even in high blood pressure you can still have areas that are comparably low pressure. 

**TDLR** It's not a much of a load in the first place.