The pulse beat is measured by the

The lumen of a vein is wider because ........

Which vessel supplies blood to the heart muscle?

Assertion : When there is a fall in the blood pressure due to loss of blood volume,this is compensated by vasoconstriction of veins.
Reason : Veins hold the extra amount of blood which can be shifted to the arteries as required.

In the given figure,what do $A, B,$ and $C$ represent respectively?

What are blood vessels composed of?