Final answer:
The pulmonary trunk is the vessel that carries blood from the right ventricle to the lungs for oxygenation, where the pulmonary valve prevents backflow, and the pulmonary veins return oxygenated blood to the heart.
Step-by-step explanation:
The vessel that carries blood from the right ventricle to the lungs where gas exchange occurs is the pulmonary trunk. This large arterial vessel exits the right ventricle and at its base has a pulmonary valve, also known as the pulmonary semilunar valve, which prevents backflow of blood into the right ventricle. The pulmonary trunk then divides into the left and right pulmonary arteries, which deliver the blood to each lung for oxygenation.
After picking up oxygen and releasing carbon dioxide in the lungs, the now oxygenated blood is carried back to the left atrium by four pulmonary veins. This concludes the pulmonary circuit of blood flow, which is crucial for gas exchange and ensuring that oxygenated blood is supplied to the systemic circuit of the body.