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
I don’t know that I would call it “constantly” changing. It does pulse from the pumping of the heart, which is why blood pressure has two numbers, the first being the high-pressure mode when the blood is shoved through the system by a heart contraction, and the second being the pressure in the “relaxed”/heart chamber refilling mode, but if you aren’t changing your state (don’t jump up and start running after sitting down a while, or something), the pressure pattern stays pretty constant.
We have some voluntary control and a lot of involuntary control on the compression of the veins (which are not rigid like glass but more like a rubbery hose) so overall system pressure can be modified by changes in how much the body presses on the veins (like how you can squeeze your neck muscles and make your face turn red because you increased pressure and slowed flow). FLow can be constricted a bit and since the volume of blood flow is “constant” (as per the heart pumping process if heart rate stays unchanged), the pressure rises if space is constricted, speeding up the flow through the system where constricted, usually. Similar pressure changes can happen if the heart increases its rate of pumping, of course.
And of course the blood itself is a viscous liquid so it can change viscosity (resistance to flow) depending on lots of things but mostly chemistry (it is a mix of solids like cells and solution or salty water, in effect), and cause the pressure to change depending on how hard the liquid is resisting its push by the heart.
I think it is important to note, or remember, that the vein system itself is somewhat flexible so the veins do expand and contract a bit in response to pressure during pumping by the heart. Things can happen to the vessels though, over time, and make the vessels a lot less flexible, or even constrict them (arteriosclerosis, hard deposits on the vessels which block flow over time) and thus make pressure increase overall, because vessels can’t expand in response to heart pulses (never mind the parts where the actual open space fills in by plaque or whatever).
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
I don’t know that I would call it “constantly” changing. It does pulse from the pumping of the heart, which is why blood pressure has two numbers, the first being the high-pressure mode when the blood is shoved through the system by a heart contraction, and the second being the pressure in the “relaxed”/heart chamber refilling mode, but if you aren’t changing your state (don’t jump up and start running after sitting down a while, or something), the pressure pattern stays pretty constant.
We have some voluntary control and a lot of involuntary control on the compression of the veins (which are not rigid like glass but more like a rubbery hose) so overall system pressure can be modified by changes in how much the body presses on the veins (like how you can squeeze your neck muscles and make your face turn red because you increased pressure and slowed flow). FLow can be constricted a bit and since the volume of blood flow is “constant” (as per the heart pumping process if heart rate stays unchanged), the pressure rises if space is constricted, speeding up the flow through the system where constricted, usually. Similar pressure changes can happen if the heart increases its rate of pumping, of course.
And of course the blood itself is a viscous liquid so it can change viscosity (resistance to flow) depending on lots of things but mostly chemistry (it is a mix of solids like cells and solution or salty water, in effect), and cause the pressure to change depending on how hard the liquid is resisting its push by the heart.
I think it is important to note, or remember, that the vein system itself is somewhat flexible so the veins do expand and contract a bit in response to pressure during pumping by the heart. Things can happen to the vessels though, over time, and make the vessels a lot less flexible, or even constrict them (arteriosclerosis, hard deposits on the vessels which block flow over time) and thus make pressure increase overall, because vessels can’t expand in response to heart pulses (never mind the parts where the actual open space fills in by plaque or whatever).
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