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How is blood pressure in our body constant?

  1. Jun 9, 2015 #1
    Generally pressure in a liquid changes with height at which we measure. But still blood pressure remains almost same throughout the body. How is this possible?
     
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  3. Jun 9, 2015 #2

    DEvens

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    Welcome to the forum.

    On a detailed level, of course there is variation in pressure. You experience this fairly directly even in such relatively minor changes as between standing upright and laying down.

    However, the blood vessels are not passive pipes. They have a fairly sophisticated system of muscles and valves. When they are working correctly they help the blood flow move along, and keep the pressure regulated. Arteries tend toward having linings of muscle to help flow along. Veins tend toward having valves that help prevent backward flow. You can see what happens when these are not working properly if you google up varicose veins.
     
    Last edited: Jun 9, 2015
  4. Jun 9, 2015 #3
    Blood pressure varies with effort and intake of food and emotional state. Blood pressure is adjusted to maintain optimal blood flow. There are baroreceptors in the aortic arch and carotid sinuses. These send signal to the medulla oblongata which controls the heart rate and blood vessels which adjust the resistance to flow by adjusting the tension in the vessels walls which widens or constricts the blood vessels. These muscles are also affected by adrenal hormone epinephrine and norepinephrine which contract the vessels thus increasing systolic blood pressure. The pressure differential due to height is small compared to the actual blood pressure.
     
  5. Jun 10, 2015 #4

    FactChecker

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    I am not an expert in this, but here is my two cents: Blood in the body is not in a simple vertical column. There are one-way valves throughout the vanes and arteries that limit how much the blood in the head pushes down on the blood in the toes, increasing pressure in the toes. That being said, there still is some difference in blood pressure based on height. That is why an accurate blood pressure is taken with the person in specific positions.
     
  6. Jun 10, 2015 #5
    The valves in the vessel are what are know as check valves, they prevent the blood from moving up stream in the body when the muscles in the vessels contract, keeping the blood moving in one direction.
     
  7. Jul 6, 2015 #6
    Blood pressure is not constant. It varies considerably.

    First there is the systolic and diastolic pressure in the aorta and other blood vessels. This doesn't count for much variation.

    The majority of the variation comes from the heart and blood vessels themselves. The right atrial pressure is 5 mmHg. It rises steadily as it goes through the pulmonary circulation. The left ventricular pressure starts off low and then gets real high. The aortic pressure goes up to 120 mmHg. As the arteries branch it gets lower and lower since if it didn't the arteries would rupture and we wouldn't even exist. It is around 80 mmHg in the capillaries and venules. As venules merge into veins the blood pressure lowers even more until it gets back to the right atrium at 5 mmHg.
     
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