Question

Blood flows from legs to heart, against the gravity through the veins because
a. walls of veins are thick
b. walls of veins are less rigid
c. walls of veins are rigid
d. walls of veins have valves
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Answer 1

Answer:

Blood flows from legs to heart, against the gravity through the veins becaused. walls of veins have valves

Explanation:

The valves close when blood starts to flow in one direction, so that blood in the veins can only flow in the direction back to the heart, which is up the legs. ... So it is a combination of blood pressure from the heart's pumping action, the valves, and muscle movement that gets the blood up the legs against gravity.

Answer 2

Answer:

Walls of veins have valves

Valves prevent the backflow of blood by gravity.

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