Lung Surfactant and Factors affecting its maturation

Origin- Type II alveolar cells and Lamellar bodies

Recycling- 90% is reprocessed, average time for turnover is around 10 hours.
CPAP can prevent excessive loss of surfactant drainage into airways by decreasing depth and length of respiration.

Phophatidylcholine ( 70-80%) and phosphatidylglycerol (5-10%)
Phosphatidylinositol, Phosphatidylserine,Phosphatidylethalomine – 10%
Other lipids- 10%, 2% surfactant lipids
Surfactant Proteins- SP-A, SP-B, SP-C, SP-D (5-10%)

Decreases surface tension of alveoli in Laplace equation ie P= 2 gamma/ r

Factors Affecting Surfactant maturation-

1. Glucocorticoids- Intrinsic cortisol accelerates surfactant maturation. Dexamethasone administered increases expression of beta-adrenergic receptors with resultant increase in surfactant production.

2.Beta- adrenergic Drugs- Terbutalline, Formeterol increase cAMP and increase production and secretion of Surfactant

3. Thyroid Hormones- T4 has enhancing property on lung maturation and surfactant secretion however, it does not cross placenta.

4.Prolactin is under study. However low prolactin has been seen in infants with RDS.

5.Epidermal growth factor- Has shown to increase SP-A and L:S ratio in non-human models.

6. Fibroblast pneumocyte factor- under study

7. Insulin- delays the maturation of alveolar type II cells and decrease production of saturated Phosphatidylcholine. It inhibits the expression of SP-A gene.

8, Testosterone- delays the lung maturation through its action on lung fibroblast.

Errors of Surfactant Metabolism-
Polymorphism of SP-A expression- predisposition to sever RSV infection and increase risk for BPD.
SP-B polymorhism- RDS 
SP-C deficiency- Interstitial Lung disease
SP-D- Alveolar accumulation of lipids and proteins.

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