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What is the speed of blood through the veins in humans?
The speed at which blood circulates throughout the body varies. Blood moves at top speed via the arteries – 1.8 km/h or 500 mm/sec. Blood running through the veins has a lower speed, about half a kilometer per hour or 150 mm/sec.Blood flow refers to the movement of blood through the vessels from arteries to the capillaries and then into the veins. Pressure is a measure of the force that the blood exerts against the vessel walls as it moves the blood through the vessels. Like all fluids, blood flows from a high pressure area to a region with lower pressure. Blood flows in the same direction as the decreasing pressure gradient: arteries to capillaries to veins.

The rate, or velocity, of blood flow varies inversely with the total cross-sectional area of the blood vessels. As the total cross-sectional area of the vessels increases, the velocity of flow decreases. Blood flow is slowest in the capillaries, which allows time for exchange of gases and nutrients. 


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