Surfactant: A whitish milky substance consisting of lipids and proteins that are secreted by type II alveolar epithelial cells that line the alveoli. It consists of 90% lipids (mostly phospholipids) and 10% proteins. There are four main surfactant proteins: surfactant protein-A (SP-A), SP-B, SP-C, and SP-C. SP-B and SP-C are very lipid-soluble and serve critical role in a mechanism which prevents the alveoli from collapsing at the end of a breath. SP-A and SP-D are more water-soluble and appear to have important roles in lung host defense.


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  1. Source: RDCRN (NCATS/NIH): cms/ rld/ Learn-More/ Glossary

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