Pulmonary surfactant is secreted by (AIIMS Nov 2012)
|A||Type I pneumocytes|
|B||Type II pneumocytes|
|D||Bronchial epithelial cells|
Type II pneumocytes
Clara cells also produce surfactant components
The Type I pneumocyte is a very large, thin (squamous) cell stretched over a very large area.
This cell cannot replicate and is susceptible to a large number of toxic insults.
Type I pneumocytes are responsible for gas exchange occurring in the alveoli.
The Type II granular pneumocyte is a roughly cuboidal cell that is usually found at the alveolar septal junctions.
Type II cells cover about 5% of the surface area of the alveoli, whereas type I pneumocytes (because of their squamous shape) cover 95% of the total area.
Even though they cover less surface area, type II cells greatly out-number type I cells.
Type II cells are responsible for the production and secretion of surfactant.
The Type II pneumocyte can replicate in the alveoli and will replicate to replace damaged Type I pneumocytes
Type II cells secrete surfactant to lower the surface tension of water and allows the membrane to separate thereby increasing the capability to exchange gases.
The alveoli have an innate tendency to collapse because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids, which are called surfactants, and pores help to equalize pressures and prevent collapse.
Infant respiratory distress syndrome (IRDS) is a syndrome caused by lack of surfactant in the lungs of premature infants (surfactant secretion starts at 28 th week of gestation).