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Surfactant composition
and action
Surfactant is produced in
the lungs of the unborn baby. At approximately week 20 the
components start to appear however it is not until much later
in pregnancy that the surfactant becomes mature enough to
work correctly.
Surfactant is a complex
substance containing phospholipids (fats) and four
different types of surfactant proteins: hydrophilic
(water-attracting) proteins SP-A and SP-D
and the hydrophobic (water-repelling) proteins SP-B
and SP-C. These latter proteins, SP-B and
SP-C (also present in Curosurf),
are essential for the uniform spreading of the surfactant
throughout the lung.
The main role of surfactant
is to prevent collapse of the alveoli thereby reducing the
effort needed to expand the lungs during inspiration (breathing
in) and allow gas exchange to take place. Surfactant therefore
helps breathing to be relatively effortless.
During expiration (breathing
out) the lungs have a tendency to collapse, if they are allowed
to do so then a much greater inspiratory effort is required
to open them with the next breath. Surfactant prevents this
by reducing surface tension throughout the lung; surface tension
is the force present within the alveoli of the lungs that
courses them to collapse and stick together during expiration.
Surfactant forms a very thin film which covers the surface
of the alveolar cells; the components of surfactant work together
to reduce surface tension and therefore reduce the tendency
of the alveoli to collapse during expiration. The lungs are
less stiff (improved pulmonary compliance) and therefore reduced
effort is needed to expand the lungs and making breathing
easier.
The natural production
of surfactant increases at approximately week 30 to 32 and
babies born after the end of the 32nd
week usually have sufficient surfactant to breath normally.
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