How is your blood pressure constantly changing when you presumably have a relatively fixed amount of blood in a fixed amount of vein?

Question

I get that your heart can pump harder and whatnot, but when it’s a fairly closed system pumping the same blood around how does that actually increase the pressure?

In: 12

Answer 1

Relatively fixed amount of blood, but dynamic size of pipes since blood vessels are not fixed dimensions. Tighter blood vessels equates to high blood pressure.

Answer 2

Relatively fixed amount of blood, but dynamic size of pipes since blood vessels are not fixed dimensions. Tighter blood vessels equates to high blood pressure.