Surfactant

This is a material lining the alveoli, composed of phospholipids, lipoproteins. The main component of surfactant is dipalmitoylphosphatidylcholine, which accounts for up to 80% of all phospholipids present in surfactant. In addition, there are hydrophobic proteins, the amount of which is not more than 10-20%. Surfactant is synthesized by type II alveolar cells. It reduces surface tension, protects alveoli from collapse, and prevents them from sticking together.

When there is a lack of surfactant due to prematurity, lung immaturity, or accelerated degradation due to hypoxia and acidosis, the alveoli collapse upon exhalation, leading to the formation of atelectasis (collapsed non-ventilated areas of the lungs). Lung ventilation decreases. Hypoxia and acidosis occur. Hypoxia and acidosis suppress surfactant synthesis. Due to hypoxia, pulmonary vascular resistance increases, leading to shunting from right to left, resulting in persistent pulmonary circulation. Increased pulmonary vascular resistance and decreased pulmonary circulation damage the endothelium and alveolar epithelium, increasing endothelial permeability and allowing plasma proteins to enter the alveoli, forming hyaline membranes – rings composed of plasma proteins.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė