Which of the following is the respiratory membrane composed of?
A) respiratory bronchioles and alveolar ducts
B) bronchioles and alveolar sacs
C) alveolar sacs and alveolar ducts
D) alveolar and capillary walls and their fused basement membranes
The correct answer and explanation is :
The correct answer is:
D) alveolar and capillary walls and their fused basement membranes
Explanation:
The respiratory membrane is the thin barrier that separates the air in the alveoli (air sacs in the lungs) from the blood in the capillaries. It is responsible for gas exchange (oxygen and carbon dioxide) between the air in the alveoli and the blood in the capillaries.
This membrane is composed of several layers, including:
- The alveolar epithelium (alveolar walls): These are the thin epithelial cells (mainly type I alveolar cells) that line the alveoli. These cells are very thin and provide a minimal barrier for gas exchange.
- The capillary endothelium (capillary walls): The capillary walls are also composed of endothelial cells, which are similarly thin to facilitate efficient gas exchange.
- The fused basement membranes: Between the alveolar epithelium and the capillary endothelium is a shared, fused basement membrane. This fused layer of basement membranes ensures that the air in the alveoli is in close contact with the blood in the capillaries, making the gas exchange process more efficient.
The respiratory membrane allows oxygen to diffuse from the alveolar air into the blood in the capillaries and carbon dioxide to diffuse in the opposite direction, from the blood into the alveoli to be exhaled.
Why other options are incorrect:
- A) respiratory bronchioles and alveolar ducts: These structures are involved in the conduction and transport of air to the alveoli but are not directly responsible for gas exchange. They are part of the airway system, not the respiratory membrane.
- B) bronchioles and alveolar sacs: The bronchioles are the smaller branches of the airway, and alveolar sacs are collections of alveoli, but neither of these alone forms the respiratory membrane.
- C) alveolar sacs and alveolar ducts: These are components of the alveolar region, but they do not directly represent the respiratory membrane, which specifically involves the alveolar walls, capillary walls, and the fused basement membrane between them.
In conclusion, the respiratory membrane is made up of the alveolar and capillary walls along with their fused basement membranes, and it is essential for efficient gas exchange.