Question

What is the function and dysfunction of water in the alveolus?

Answer 1

The alveoli contains a mixture of surfactant and water known as the alveolar fluid. This fluid is accumulated in alveoli through leakage from the capillaries surrounding the alveoli. The important functions of the alveolar fluid are:

1. it acts as a protective layer of alveoli that protects its epithelium layer from damage caused by inspired air and the irritants and toxins contained in it.
2. The alveolar fluid contains surfactant and the water which helps improve lung compliance. It also helps reduce surface tension at the air-liquid interface.
3. Alveolar fluid also acts as solvent for molecules contained in surfactant, cytokines.
4. Alveolar fluid contains macrophages and other immune cells that helps prevent lung infection.
5. Alveolar fluid helps in diffusion of O2 and CO2 across the alveolar membrane.
The alveolar fluid is tightly regulated through reabsorption by epithelial cells and removal of water during expiration. When these mechanism gets impaired it results either in accumulation or depletion of alveolar fluid.
When the fluid in the alveoli is not reabsorbed properly it results in accumulation in the alveoli. This cause pulmonary edema and impaired gas exchange which may lead to hypoxia.
When the alveolar fluid decreases below the normal level it reduces lung compliance. Decreased alveolar fluid is seen in cystic fibrosis which leads to impaired mucus clearance from lungs.