The respiratory membrane, through which a molecule of carbon dioxide must travel in order to diffuse from the blood into the alveoli, is composed of alveolar epithelium, a fused basement membrane, and a capillary endothelium.

a. True

b. False

A. True

Explanation:

There are two sites where exchange of gases takes place, one is the exchange of gases between alveoli and blood and the second is exchange of gases between blood and tissue. In this question we are discussing about the about the diffusion of CO2 from blood to the alveoli for exhalation. CO2 must cross the diffusion membrane.

Diffusion membrane: The alveolar wall is thin and has rich network of capillaries. Due to this network, alveolar wall looks like a sheet of flowing blood and is called the diffusion membrane or alveolar-capillary membrane. This diffusion membrane is made up of three layers:

a. The thin squamous epithelium of alveoli

b. Endothelial lining of blood capillaries

c. a fused basement membrane between epithelium of alveoli and endothelium of capillaries.

All these three layers make the total thickness of about 0.2 mm.