Why does blood travelling from the heart to the lungs (pulmonary arteries) require such high pressure?
It doesnt – the blood travelling from the heart to the lungs via the pulmonary arteries (arteries leave the heart) is under low pressure otherwise it would flood the lungs. Once it has been oxygenated it returns to the heart via the pulmonary veins still under low pressure (as nothing has increased the pressure in the lungs) into the left ventricle which is the most heavily muscled and is pumped through into the aorta under enormous pressure in order to perfuse the rest of the body with oxygenated blood.
