2007-12-28 05:10:06 · 4 answers · asked by grahmcracker 1 in Science & Mathematics ➔ Biology
please help and thank you in advance!
2007-12-28 05:12:01 · update #1
Veins carry blood back towards the heart. Because veins are narrow (unlike, say, arteries), the use the valves to build up pressure, allowing blood to be moved back to the heart for oxygenation. The valves are also used to prevent the back-flow of blood, so the blood doesn't move away from the heart.
2007-12-28 05:17:50 · answer #1 · answered by ¿ /\/ 馬 ? 7 · 0⤊ 1⤋
Valves In Veins
2016-10-05 12:33:40 · answer #2 · answered by ? 4 · 0⤊ 0⤋
The pressure of the blood flowing through the arteries is tremendous. That pressure keeps the blood flowing no matter what the position of the organism.
However, the blood pressure is greatly reduced as it passes through the capillaries. While the heart is contracting (systole), the pressure of the blood on the walls of the arteries should be about 110 mm of mercury (mmHg). When the heart relaxes (diastole), the pressure drops to about 70-80 mmHg. However, as the arteries branch and branch and ultimately become capillaries, both the systolic and diastolic pressures are dramatically reduced. The blood pressure at the distal end of the capillary (where the blood comes OUT of the capillary) is reduced to about 15 mmHg during systole and only a few mmHg during diastole. As the blood goes into larger veins, the pressure during both systole and diastole will drop to nearly zero.
If there is almost no blood pressure pushing the blood back to the heart the blood, during diastole, would flow backwards due to gravity.
Valves prevent that backward flow. The valves are cup like structures that have one end directly attached to the wall of the vein. The other end is not directly attached to the vein wall -- it is like a "U" shape. Due to the shape, when the heart relaxes and the blood begins to flow backward, the 'cups' (each is called a cusp) catch the blood. The unattached ends hit each other and seal the vein from blood flowing backwards.
All valves are found in veins EXCEPT for two. Those two are in the heart where the pulmonary artery and the aorta exit the heart.
2007-12-28 06:26:08 · answer #3 · answered by academicjoq 7 · 1⤊ 0⤋
This Site Might Help You.
RE:
why are there valves in veins?
2015-08-18 02:37:37 · answer #4 · answered by Anonymous · 0⤊ 0⤋
To prevent backflow of blood. Arteries don't need them because the pressure from the heart is enough to keep the blood moving forward. But veins carry blood from the rest of the body to the heart and so need valves to keep the blood moving in one direction only.
2007-12-28 12:09:34 · answer #5 · answered by abcd 3 · 0⤊ 0⤋
the valves are there to stop blood flowing backwards in other words when your heart pumps blood it goes round the body via valves opening and closing if the valves were not there the blood would not carry oxygen and eventually not be able to sustain your bodies balance and then ----------------!
2007-12-28 05:17:07 · answer #6 · answered by Anonymous · 0⤊ 0⤋
to egulates the flow of blood inside the vein
2007-12-28 05:36:39 · answer #7 · answered by Anonymous · 0⤊ 0⤋
To make sure the blood flows one way only - back towards the heart.
2007-12-28 05:15:06 · answer #8 · answered by Anonymous · 0⤊ 0⤋
norcot is right, they're to prevent the backflow of blood, which could cause stroke or other issues.
2007-12-28 05:17:55 · answer #9 · answered by allyp 2 · 0⤊ 0⤋