I'm studying human physiology. And there is a often repeated notion that blood flows "from areas of high pressure to lower pressure". I was wondering why that is so. However there is no real explanation for it. I understand that in a gradient the force points into the direction of low pressure. Further research on the web has just caused more confusion, because there are certain voices saying that it is a true notion and certain voices claiming that this is not true and instead energy arguments should be used. I have read about Poiseuilles law, Bernoullis law and several more and they just seem to contradict eachother in the end.
So my question is: In general, does a fluid always flow from high pressure to low pressure? Strictly related to the human body, does blood (in the "closed" system) always flow from high pressure to low pressure? Why?
It'd be great if somebody could enlighten me. I'm also sure that answering this question would help many others as well, as it is (in my view) a very basic question but very important for anybody trying to learn/understand physiology.