Question

In the lungs, the air is separated from the venous blood through
A. Squamous epithelium + endothelium of blood vessel
B. Squamous epithelium + tunica media blood vessel
C. Transitional epithelium + tunica external blood vessel
D. None of the above

Answer 1

Venous blood refers to the deoxygenated blood. Deoxygenated blood is the blood that has a high percentage of carbon dioxide and a low percentage of oxygen in it. Moreover, the air and blood in the lungs are separated by the double membrane of alveoli and blood vessels.

Complete step by step answer: In the lungs, the gaseous exchange occurs in two places. These two places are –
1. Alveolar layer
2. Cellular layer or the tissue layer
Alveoli are the small sacs in the lungs that contain air. They increase the surface area of the lungs several-fold. Not only this but alveoli are also the primary site for the exchange of gases. The gaseous exchange or the exchange of the gases occurs between the blood of the blood vessels and the tissues of the alveoli. Now the layer where the diffusion of gases occurs is known as the diffusion layer. It is made up of two layers chiefly, the squamous epithelium of the alveolar walls of the lungs that is very thin, and the endothelium or the innermost lining of the capillaries of the alveoli. This diffusion layer separates the air from the blood. The total thickness of this diffusion membrane is, however, far less than the millimeter. Thus, based on the above information we can conclude that in the lungs, the air is separated from the venous blood through the Squamous epithelium and the endothelium of the blood vessels.
Hence, the correct answer is option (A).

Note: The primary gases, oxygen, and carbon dioxide are exchanged at the walls of the alveoli by the process of simple diffusion. This exchange occurs based on the gradient of the pressure and the concentration. Factors like the solubility of gases and the thicknesses of the membranes are also important for the rate of diffusion.