Question

why are valves present in heart and veins

Answer 1

In order to prevent the back flow of blood from ventricle to atria

Answer 2

Answer:

• Valves present in the heart and veins prevent the backflow of blood, that is, flow of blood in the direction opposite to that in which it is flowing.

Explanation:

• In the heart,

1. Blood moves from the vena cavas and pulmonary vein to the auricles,  from auricles to ventricles and from ventricles into the aorta and pulmonary artery under huge pressure.
2. This pressure is necessary to ensure that the :

• the entire blood from the auricles is pushed into the ventricles,
• blood from the ventricles enter into the aorta and reach all the distant parts of the body and that from the pulmonary artery reaches the lungs.

    3. During the application of pressure by the contraction of the heart  heart, there is chance that some blood may flow backwards from the auricles back into the vena cavas  or the pulmonary vein or from the ventricles back into the auricles or from the aorta and the pulmonary artery into the ventricles.

     4. To prevent these there are valves present in between:

1. Vena cavas, pulmonary veins and auricles.
2. auricles and ventricles.
3. ventricles and aorta, pulmonary artery.

• In the veins,

1. Veins have a wider lumen as compared to that of the artery so the chance of back flow of blood in veins is high.
2. Blood flows in the artery under high pressure so there is unidirectional movement of blood, but in the vein the blood pressure being low the chances of back-flow of blood is high.