Pulmonary surfactant

A complex mixture of lipids and proteins that reduces surface tension in the lungs

Pulmonary Surfactant
Pulmonary surfactant as seen under a microscope
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Pulmonary surfactant is a complex mixture of lipids and proteins that is secreted by the epithelial cells of the alveoli in the lungs. Its primary function is to reduce the surface tension at the air-liquid interface within the alveoli, preventing alveolar collapse and thereby maintaining proper lung function.

Structure and Composition

Pulmonary surfactant is composed of approximately 90% lipids and 10% proteins. The most abundant lipid is dipalmitoylphosphatidylcholine (DPPC), a phospholipid that plays a critical role in reducing surface tension. The protein component includes surfactant proteins A, B, C, and D, which are involved in surfactant metabolism and host defense.

Function

The primary function of pulmonary surfactant is to lower the surface tension of the fluid lining the alveoli. This reduction in surface tension prevents the alveoli from collapsing during exhalation and reduces the work of breathing. Surfactant also plays a role in innate immunity by binding to pathogens and facilitating their clearance by alveolar macrophages.

Synthesis and Secretion

Surfactant is synthesized and secreted by type II alveolar cells in the lungs. The synthesis of surfactant begins in the fetal lung around the 24th week of gestation, with significant production occurring by the 34th week. This timing is critical for the transition to air breathing at birth.

Clinical Significance

A deficiency in pulmonary surfactant can lead to respiratory distress syndrome (RDS), particularly in premature infants whose lungs have not yet produced adequate amounts of surfactant. Surfactant replacement therapy is a common treatment for neonatal RDS, involving the administration of exogenous surfactant to the infant's lungs.

Research and Developments

Ongoing research is focused on improving surfactant replacement therapies and understanding the role of surfactant in various lung diseases, including acute respiratory distress syndrome (ARDS) in adults.

Also see

• Alveolus
• Respiratory distress syndrome
• Type II alveolar cells
• Acute respiratory distress syndrome