Why are animals like spiders, geckos, … not affected by blood running into their head when staying head down for a long period of time?

Question

Why are animals like spiders, geckos, … not affected by blood running into their head when staying head down for a long period of time?

In: 9

Answer 1

I’d like to add that the animals mentioned have their heads pretty much horizontal to their hearts, while ours are vertical in most situations. Our hearts work much harder to pump blood against gravity upwards into our head, so when we are upside down the blood rushes into our heads.