Everybody's answer above is correct. They only neglected to mention that the reason the blood does not flow backward is, the veins have one-way valves. When the heart contracts the valves in the veins open and the blood flows forward. When the heart expands to receive more blood, the valves in the veins close so that the blood does not flow back from the way it came.
Answered: Tue, 15 Dec 2009
You found this answer helpful
Disclaimer: These answers are for your information only and not intended to replace your relationship with your treating physician.
This is a short, free answer.
For a more detailed, immediate answer, try our premium service [Sample answer]