why is it low here?
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Basically because they are further away from the source of the pressure - the heart
The cardiovascualar system is like the road network system
The aorta (large blood vessel that comes right off the heart) is like the "autobahn" lots of traffic (many red blood cells) and lots of pressure ( no speed limit = cars go very fast like 100mph or more)
the arterioles and capillaries are tiny, they are like streets and driveways - they accommodate only one or very few red blood cells and must go slow (low pressure) (also you dont want cars going 100mph in your driveway)
also the smaller vessels aren't quite as thick or strong, so if there was a massive amount of pressure in them they could pop and cause internal bleeding, Veins are usually quite thin since there is very low blood pressure in them
**** But the Main reason as to "WHY" would be for the diffusion of nutrients and waste it takes time for oxygen and other nutrients to go from the red blood cells to the cells that line the capillaries. so the red blood cells must go slow (low pressure) so that this may happen.
Try getting groceries out a car going past your house when its going 15 -100 mph - it would be difficult.
hope this helps =)
The cardiovascualar system is like the road network system
The aorta (large blood vessel that comes right off the heart) is like the "autobahn" lots of traffic (many red blood cells) and lots of pressure ( no speed limit = cars go very fast like 100mph or more)
the arterioles and capillaries are tiny, they are like streets and driveways - they accommodate only one or very few red blood cells and must go slow (low pressure) (also you dont want cars going 100mph in your driveway)
also the smaller vessels aren't quite as thick or strong, so if there was a massive amount of pressure in them they could pop and cause internal bleeding, Veins are usually quite thin since there is very low blood pressure in them
**** But the Main reason as to "WHY" would be for the diffusion of nutrients and waste it takes time for oxygen and other nutrients to go from the red blood cells to the cells that line the capillaries. so the red blood cells must go slow (low pressure) so that this may happen.
Try getting groceries out a car going past your house when its going 15 -100 mph - it would be difficult.
hope this helps =)
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The other answer is correct, but blood pressure does not drop very significantly. This is because the vessels get smaller, and as they get smaller and further away from the heart, the blood pressure remains nearly stable. The reason for this is because when fluids are pushed through smaller vessels, their pressure increases. Compare that to the end of a fire hose. The tip of the hose is narrow because fluid pressure increases as it goes through narrow spaces.
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Why? The answer is simple and straightforward, and related more to physics than biology: the walls of vascular tissue is somewhat elastic. When the blood is pumped from the heart, the pressure on the walls of the arteries proximal to the heart is great, but a lot of that force is absorbed by the elasticity of the walls of the vasculature. As more distance is covered by the blood in its circulatory path, more kinetic energy is dissipated by flow resistance and the vascular walls. By the time the blood reaches the capillary networks, the blood pressure has dropped significantly.