Hi, I’m really struggling with the relationship between blood pressure and blood flow. I’m hoping that somebody could really dumb the answer down for me as much as possible.
Like, I think I understand hydrostatic pressure. When it comes to the leaky vessels, you need more pressure to squeeze stuff out in those areas. And then osmosis or passive transport whatever balances things out again afterwards. That makes sense to me.
But then why would the kidneys for example want to raise blood pressure in other areas? Like, just high blood pressure in general, say, in the arteries. Why constrict those? Why would you want that? I kind of understand how blood pressure = cardiac output x resistance. Wouldn’t that mean blood flow goes down? Increasing resistance to increase blood pressure?
I mean, plus the damage that high blood pressure is supposed to do over time. And this is then on top of impeded blood flow. And so, I just keep hearing how various systems or vessels etc constrict to increase pressure on purpose. Why would the body want that?
Basically, what is the point of high blood pressure? It seems like it sucks. Thanks.
In: 4
Blood isn’t the same all over the body. The lungs exchange gases from the blood and the blood in lungs is rich in oxygen. That blood has to be PUSHED to the rest of the body.
The liver absorbs nutrients from blood, processes them and releases nutrients that the body needs. This blood needs to be PUSHED to the rest of the body.
The brain keeps sucking oxygen and sugar and other nutrients all the time. It needs blood replenished at a nearly constant rate all the time.
The pump your body has to push the blood is the heart. The heart pushes the blood at just enough rate to keep your organs perfused with the right amount of blood.
Your nutrient and oxygen demand goes up when you exercise, and the heart compensates in the short term by beating faster, and in the longer term by becoming stronger to push more blood per pump.
All this artery clogging is recent (rich abundant food due to agriculture) and irrelevant to biology. As long as you live long enough to procreate, biology doesn’t improve the subsequent generations. Since high BP and heart diseases don’t kill you quickly, genetics hasn’t kicked in to remove it.
So in short, you have just enough blood pressure to keep you alive.
It seems like you’re asking two questions here:
1. What is the relationship between blood pressure and blood flow? 2. Why does the body constrict blood vessels to create higher blood pressure?
It seems like you’ve got a pretty decent understanding already. Basically, the body constricts or dilates blood vessels to control how much blood is going to a specific area of the body. For example, blood vessels near the surface will constrict when the body is cold, in order to reduce the blood flow and therefore heat transfer at the surface of the body, and to allow vital organs to receive greater blood flow due to the constricting of those surface vessels. Another example is during exercise, blood vessels will dilate and heart rate increases to allow more oxygen to be transported throughout the body. During stress, heart rate increases and blood vessels constrict to allow blood to be used in the most necessary places in a fight or flight response.
Because the body is a closed system with a variable pump so to speak (the heart), vasoconstriction will cause higher blood pressure. This is more a product of the flow restriction, which is how the body redirects blood for specific needs. Chronic blood pressure is an issue, as the increased blood drag wears on the walls of arteries over time. However, small increases in blood pressure are normal due to small stress responses we experience in our day to day lives.
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