Question

how blood enter into veins from artery

Answer 1

The veins and arteries are connected together with cappilaries where gaseous  (CO2 and O2) exchange took place and blood enter veins through capillaries from arteries

Answer 2

Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poorblood from the body into the right atrium. ... As the ventricle contracts,blood leaves the heart through thepulmonic valve, into the pulmonaryartery and to the lungs, where it is oxygenated