What are the components of the alveolocapillary membrane?

• A. Alveolar epithelium and capillary endothelium
• B. Alveolar epithelium, merged basement membranes, and capillary epithelium
• C. Nasal epithelium and bronchial epithelium
• D. Capillary epithelium and interstitial fluid

Answer: (B)

The alveolocapillary membrane is a critical structure in the respiratory system, playing a vital role in gas exchange between the alveoli (air sacs in the lungs) and the capillaries (small blood vessels). The correct answer identifies the key components that make up this membrane.

The alveolocapillary membrane consists of the alveolar epithelium, which is the thin layer of cells lining the alveoli, and the capillary endothelium, which is the thin layer of cells lining the small blood vessels. These two cell layers are separated by a very thin interstitial space, with their basement membranes merged together. This merging creates an incredibly thin barrier that facilitates efficient diffusion of oxygen and carbon dioxide.

The inclusion of merged basement membranes emphasizes the unique structural feature of this membrane, as it allows for a very short diffusion distance, which is essential for the rapid exchange of gases required for effective respiration. This anatomical arrangement ensures that any gases in the alveoli can move quickly into the bloodstream and that carbon dioxide can move out of the blood into the alveoli for exhalation.

In contrast, the other options do not accurately reflect the components of the alveolocapillary membrane. For instance, nasal epithelium and