Which one of the following statements about pulmonary surfactant is correct?

A.It is increased in the respiratory distress syndrme in the newborn.
B.It increases the stickiness of the alveolar walls.
C. It is glycoprotein.
D.It accounts for the pulmonary lesion in mucoviscidosis.
E, It is reduced by prolonged breathing of 100%oxygen


Ans: ?E

Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells.

The proteins and lipids that comprise the surfactant have both a hydrophilic region and a hydrophobic region. By adsorbing to the air-water interface of alveoli with the hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.

Function
To increase pulmonary compliance.
To prevent atelectasis
To facilitate recruitment of collapsed airways.

Clara cells also produce a component of lung surfactant.

Alveolar surfactant has a half life of 5 to 10 hours once secreted.

It can be both broken down by macrophages and / or reabsorbed into the lamellar structures of type II pneumocytes.

Up to 90% of surfactant DPPC (dipalmitoyl phosphatidylcholine) is recycled from the alveolar space back into the type II pneumocyte. This process is beleived to occur through SP-A stimulating receptor mediated, clathrin dependant endocytosis. The other 10% is taken up by alveolar macrophages and digested.

Case Study: Conclusion- 

Breathing 100% oxygen for 48 hours has direct effects on the amount of surfactant in the lung, but probably no effect on the metabolic pathways which regulate its phospholipid composition. These differences probably occur because of metabolic changes in catabolic processes associated with the clearance of surfactant.