Oxygen and carbon dioxide are exchanged in the lungs by?

Appeared in: VSSC Nursing Officer - 2021

Explanation

Gas exchange in the lungs occurs via diffusion, a passive process where molecules move down their concentration gradient.
This movement is driven by differences in the partial pressure of gases between the alveoli and the blood.
Oxygen, having a higher partial pressure in the alveoli, moves into the blood.
Conversely, carbon dioxide has a higher partial pressure in the blood, causing it to move into the alveoli to be exhaled.

Option A: Osmosis is the movement of water across a semipermeable membrane, not the movement of respiratory gases.
Option C: Filtration is the movement of fluid and solutes through a membrane caused by a pressure difference (hydrostatic pressure), not a concentration gradient of gases.
Option D: Active transport requires energy (ATP) to move substances against their concentration gradient. Gas exchange in the lungs is a passive process.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mechanism of gas exchange in the lungs as background academic context rather than a clinical decision trigger.
Understanding that gas exchange relies on diffusion helps nurses recognize how certain conditions can impair this process. For example, in pneumonia or pulmonary edema, fluid in the alveoli increases the diffusion distance, leading to hypoxia.
This knowledge is fundamental to interpreting pulse oximetry (SpO₂) readings, which provide a non-invasive measure of the effectiveness of gas diffusion and oxygenation.
What if? If a patient develops pulmonary fibrosis, the alveolar-capillary membrane thickens. This thickening directly impedes diffusion, reducing the rate of gas exchange and often requiring supplemental oxygen therapy to increase the partial pressure gradient and improve oxygen uptake.

How to Approach the Question

First, identify the core physiological process in the question: how respiratory gases (oxygen and carbon dioxide) move in the lungs.
Recall the fundamental principles of substance transport across biological membranes.
Analyze each option: Osmosis (water movement), Diffusion (solute movement down a gradient), Filtration (pressure-driven movement), and Active Transport (energy-requiring movement against a gradient).
Connect the process of gas exchange with its definition. Gases in the lungs move from an area of higher concentration (partial pressure) to an area of lower concentration without energy.
This matches the definition of diffusion, making it the correct answer.

Concept Tested & Keywords

QcLxxMWpOkZNHF-IlrduiA

E6 Physiology Guyton 4SAE Part 2A p. 83-85

E6 Nursing Fundamentals Taylor p. 707-709

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