26.13 : 肺換気に影響を与える要因

Breathing is influenced by the alternating pressure difference between the external environment and the lungs, alveolar surface tension, lung compliance, and airway resistance.

In the alveoli, the luminal surface is lined by an aqueous alveolar fluid with a surfactant mixture of phospholipids and lipoproteins.

This alveolar surfactant reduces the attractive forces between the polar water molecules, reducing the surface tension of the alveolar fluid. As a result, less energy is required to expand the alveoli during inhalation.

Additionally, the alveolar fluid and the elastic fibers in the lung tissue increase lung compliance, reducing the effort required to stretch the lungs to fill air.

The walls of the airways, especially in smaller bronchioles, offer resistance to the air filling the lungs.

Signals from the sympathetic nervous system relax the smooth muscles in the bronchial walls, increasing their diameter to decrease the resistance.

On the other hand, the parasympathetic nervous system stimulates the contraction of the bronchial smooth muscles, or bronchoconstriction, and increases airway resistance.