How Does Venous Return = Cardiac Output?

  • #1
I'm not understanding this. To my knowledge, in normal function, the amount of blood coming into the heart is equal to the amount of blood going out. Venous return = cardiac output. But how can that be? How can the low pressure venous blood flow match the high pressure arterial blood flow? I would think the volume through the arteries would be much greater. Could someone explain this topic. Thanks for the help!
  • #2
If you have a fluid source the flow rate from it doesn't only depend on the source pressure but also the nature of the "load". The blood returning to the heart might be at a lower pressure but what resists it flowing into the heart? Compare with what resists the flow out of the heart?

Your question is a bit like asking... How can the electrical current in a circuit be the same at both terminals of a battery when the positive terminal is at a higher voltage than the negative? By the time the electricity returns to the battery it's already gone through the load, in effect there is nothing to stop it flowing back into the battery.
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