Question

The blood leaving the lungs is richer in .......... than the blood entering the lung.
A. Oxygen
B. CO2​
C. Hydrogen
D. Moisture

Answer 1

Blood leaving lungs enters the left atrium through pulmonary arteries.

Step by step answer:
Through the inferior vena cava deoxygenated venous blood enters the right atrium. From the right atrium blood goes to the right ventricles. There is a valve present between the right atrium and the right ventricle called the tricuspid valve. The tricuspid valve has three leaflet-like appearances. It prevents backward regurgitation of blood while flowing from the right atrium to the right ventricle. The right ventricle pumps this blood into the lungs through the pulmonary artery. The valve present here is a pulmonary valve. The deoxygenated blood gets oxygenated in the lungs through the alveolar exchange of gases.
In the alveoli, oxygen received through inhalation is exchanged with carbon dioxide present in the blood cell. Now, the carbon dioxide is exhaled and the blood gets oxygenated. This oxygenated blood leaves the lung through the pulmonary vein and enters the left atrium. Further, this blood is pushed into the left ventricle. The valve present here is a mitral valve or bicuspid valve. This valve has two leaflets like appearance.
From the left ventricle, the blood is pushed against the gravity and supplied to the whole body through the aorta. The valve present here is the aortic valve.

Therefore the correct answer is A, i.e., Oxygen

Note: Pulmonary artery is the only artery that carries deoxygenated blood and the pulmonary vein is the only vein in our body that carries oxygenated blood. A decrease in oxygen level in our body causes hypoxia.