Question

When someone is standing, gravity stretches the bottom of the lung down toward the floor to a greater extent than the top of the lung. What implication could this have on the flow of air in the lungs? Where does gas exchange occur in the lungs?

A. Increased airflow at the top of the lungs; gas exchange in bronchi
B. Increased airflow at the bottom of the lungs; gas exchange in alveoli
C. Decreased airflow at the top of the lungs; gas exchange in trachea
D. No effect on airflow; gas exchange in diaphragm

Answer 1

Gravity leads to increased ventilation at the bottom of the lungs due to a more negative intrapleural pressure causing more air to fill in there; gas exchange primarily occurs in the alveoli, making option (B) correct.

Step-by-step explanation:

When standing, gravity affects the lung by stretching its bottom part more than the top, leading to a difference in the intrapleural pressure. This pressure gradient results in increased ventilation at the bottom of the lung where the pressure is more negative, causing more air to fill the bottom part. Contrarily, the top is less filled with the air due to less negative pressure. Such vertical gradients in ventilation contribute to a phenomenon known as V/Q mismatch, where V stands for ventilation and Q for perfusion. Gas exchange occurs mostly in the alveoli, where the blood acquires oxygen and releases carbon dioxide. Thus, the correct answer to the question is B. Increased airflow at the bottom of the lungs; gas exchange in alveoli.