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sodium.dioxid
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Blood is in continuous contact with itself. Thus any pressure on artery blood is pressure on vein blood. So they have the same pressure. What am I missing here?
The answer is friction. Blood is a viscous fluid and rubs against the side of the vessels it passes through. The vessels exert a force on the fluid opposing its motion and reduce the pressure. In the wide, main arteries, the pressure doesn't drop much (but gravity has some effect). In the narrower arteries and arterioles the effect is much greater. The veins (which operate at much reduced pressure) also have valves in them which have an effect, too.sodium.dioxid said:You didn't quite understand the question. Blood IS in contact with itself. There is no gap in blood. I have a straw and I blow water from one end to the other end. Why is the pressure of water in the far end of the tube lower than that in the end closer to my mouth? Pressure is imparted on the entire fluid as a whole.
Edit: pushing a line of marbles from one end causes a push of the whole line of marbles. To say that pressure decreases is like saying that the marbles closer to the push are faster, which is phsically impossible because they don't go through each other.
Wikipedia said:Mean blood pressure decreases as the circulating blood moves away from the heart through arteries, capillaries and veins due to viscous losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles. Gravity affects blood pressure via hydrostatic forces (e.g. during standing) and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins.
Wikipedia said:Resistance. In the circulatory system, this is the resistance of the blood vessels. The higher the resistance, the higher the arterial pressure upstream from the resistance to blood flow. Resistance is related to vessel radius (the larger the radius, the lower the resistance), vessel length (the longer the vessel, the higher the resistance), blood viscosity, as well as the smoothness of the blood vessel walls. Smoothness is reduced by the build up of fatty deposits on the arterial walls. Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the size of blood vessels, thereby decreasing arterial pressure. Resistance, and its relation to volumetric flow rate (Q) and pressure difference between the two ends of a vessel are described by Poiseuille's Law.
Wikipedia said:Pressure drops gradually as blood flows from the major arteries, through the arterioles, the capillaries until blood is pushed up back into the heart via the venules, the veins through the vena cava with the help of the muscles. At any given pressure drop, the flow rate is determined by the resistance to the blood flow. In the arteries, with the absence of diseases, there is very little or no resistance to blood. The vessel diameter is the most principal determinant to control resistance. Compared to other smaller vessels in the body, the artery has a much bigger diameter (4mm), therefore the resistance is low.[47]
In addition, flow rate (Q) is also the product of the cross-sectional area of the vessel and the average velocity (Q=AV). Flow rate is directly proportional to the pressure drop in a tube or in this case a vessel. ∆P α Q. The relationship is further described by Poisseulle’s equation ∆P=8µlQ/πr^4.[48] As evident in the Poisseulle’s equation, although flow rate is proportional to the pressure drop, there are other factors of blood vessels that contribute towards the difference in pressure drop in bifurcations of blood vessels. These include viscosity, length of the vessel, and radius of the vessel.
sodium.dioxid said:You didn't quite understand the question. Blood IS in contact with itself. There is no gap in blood. I have a straw and I blow water from one end to the other end. Why is the pressure of water in the far end of the tube lower than that in the end closer to my mouth? Pressure is imparted on the entire fluid as a whole.
Edit: pushing a line of marbles from one end causes a push of the whole line of marbles. To say that pressure decreases is like saying that the marbles closer to the push are faster, which is phsically impossible because they don't go through each other.
I understood the question. You mentioned arterial and veinous blood. They are separated by a significant amount of passage through capillaries. Lots of friction.sodium.dioxid said:You didn't quite understand the question. Blood IS in contact with itself. There is no gap in blood. I have a straw and I blow water from one end to the other end. Why is the pressure of water in the far end of the tube lower than that in the end closer to my mouth? Pressure is imparted on the entire fluid as a whole.
Edit: pushing a line of marbles from one end causes a push of the whole line of marbles. To say that pressure decreases is like saying that the marbles closer to the push are faster, which is phsically impossible because they don't go through each other.
sodium.dioxid said:But if pressure is lower in the veins, wouldn't that mean a build up of blood in the veins?
The farther blood travels from the left ventricle, the greater the resistance it encounters in the blood vessels. This resistance is due to the narrowing of the blood vessels and the friction caused by the blood flowing through them. As a result, the force of the blood against the vessel walls decreases, leading to a drop in blood pressure.
Gravity plays a significant role in the decrease of blood pressure as it travels away from the left ventricle. When standing, the force of gravity pulls blood downwards, causing it to pool in the lower extremities. This reduces the amount of blood returning to the heart, ultimately leading to a decrease in blood pressure.
The elasticity of blood vessels also contributes to the drop in blood pressure as it moves away from the left ventricle. Blood vessels are more elastic closer to the heart, which allows them to expand and accommodate the force of blood being pumped out of the heart. As the blood travels farther from the heart, the blood vessels become less elastic, making it more difficult for them to expand and maintain high blood pressure.
The relationship between blood pressure and distance from the heart is inversely proportional. This means that as the distance from the heart increases, the blood pressure decreases. This is because the heart has to work harder to pump blood to more distant areas of the body, leading to a decrease in pressure.
Exercise can temporarily increase blood pressure, but over time, it can also improve the overall health of the cardiovascular system. Regular exercise strengthens the heart muscle, making it more efficient at pumping blood and decreasing the resistance encountered by blood vessels. This can lead to a decrease in blood pressure, even as blood travels farther from the heart.