2007-10-21 17:06:37 · 7 answers · asked by UHstd 1 in Science & Mathematics ➔ Biology
There are valves inside the veins to prevent backflow. The smooth muscle on the wall the veins contract to increase venous pressure to drive more blood into the heart. During exercise or emergency, the sympathetic nervous system increases smooth muscle contraction and thus increases venous pressure, which in turn increases the blood flow back to the heart.
2007-10-21 17:25:18 · answer #1 · answered by OKIM IM 7 · 0⤊ 0⤋
As far as I know the heart does all the work by pumping the blood around the body. Also, there are little valves in veins which keep the blood from flowing backward when it travels from the feet back to the heart. It may be that the muscles in the legs provide some support during this process.
2007-10-21 17:17:23 · answer #2 · answered by carol h 3 · 0⤊ 0⤋
which vein do u mean? generally the valves in the vein push the blood along.
2007-10-21 18:00:22 · answer #3 · answered by fabu_hotchic 2 · 0⤊ 0⤋
I believe the Autnomic Nervous System actually controls when and how much blood flows in and out of the heart, and where it goes from there.
2007-10-21 17:18:33 · answer #4 · answered by Mammy 2 · 0⤊ 0⤋
1. pressure: abour 4 - 6mm only
2. veins are valved and thin-walled so muscular contraction around them froces the blodd in them one way - up towards the heart.
answer: pressure and muscalr contraction arounnd the valved veins.
2007-10-21 17:14:14 · answer #5 · answered by Anonymous · 0⤊ 0⤋
theres 2 valves that work together
2007-10-21 17:10:19 · answer #6 · answered by crengle60 5 · 0⤊ 0⤋
i dont know about bio anything.
2007-10-21 17:14:09 · answer #7 · answered by Anonymous · 0⤊ 1⤋