Answer:
They terminate at the alveolar sacs which contain the alveoli. Here inhaled O2 is exchanged for exhaled CO2 via the pulmonary veins (which transport de-oxygenated blood with CO2), to the pulmonary arteries (which transport oxygenated blood to the body). Both veins and arteries in this system receive and pump blood from the heart (veins to the heart under low pressure, and arteries from the hear under Hugh pressure. The entire system is called the cardio-pulmonary system.