Question

The Alveolar epithelium basement membrane and lung capillary endothelium are typically 1 um thick. Under resting conditions, hemoglobin binding oxygen reaches a steady state (i.e. does not change with time) in about 0.33 seconds. Is oxygen diffusion across the alveolus a significant factor in the time required for the hemoglobin to oxygenate as it traverses the capillary? Given that the diffusion coefficient is 2x 10⁻⁵cm²s⁻¹

Answer 1

Oxygen diffusion across the alveolus is efficient due to the thin respiratory membrane and the strong pressure gradient, indicating it is not a significant factor in delaying the oxygenation of hemoglobin as blood passes through pulmonary capillaries under resting conditions.

Step-by-step explanation:

When assessing if oxygen diffusion across the alveolus is a significant factor in the time required for hemoglobin to oxygenate, it's essential to consider the thickness of the alveolar-capillary barrier and the diffusion coefficient for oxygen. The alveolar epithelium and capillary endothelium together create a respiratory membrane that is extremely thin, around 1 um (0.5 micrometers according to another cited figure) and this minimal thickness allows for efficient diffusion of gases.

The diffusion coefficient for oxygen is 2 x 10⁻⁵ cm²s⁻⁹, and given the small distance involved across the alveolar-capillary membrane, oxygen can rapidly cross this membrane. The time required for hemoglobin to reach a steady state with oxygen is approximately 0.33 seconds, which is fairly quick. Considering the rapid diffusion facilitated by the strong partial pressure gradient and the thin respiratory membrane, it suggests that oxygen diffusion is not a limiting factor in the time for hemoglobin oxygenation during the capillary traverse under resting conditions.