Q.95 Which ONE of the following is the primary function of lung surfactants?
(A) Remove dust particles from bronchi
(B) Provide immunity to respiratory tract
(C) Prevent alveoli from collapsing by decreasing surface tension
(D) Aid in carbon dioxide exchange
Lung surfactants primarily prevent alveoli from collapsing by decreasing surface tension, making option (C) correct for this CSIR NET Life Sciences question. This function stabilizes the respiratory system during breathing cycles. Detailed analysis below clarifies each option.
Option Analysis
-
(A) Remove dust particles from bronchi: Incorrect; dust removal occurs via mucociliary clearance in bronchi, involving cilia and mucus, not surfactants which act in alveoli.
-
(B) Provide immunity to respiratory tract: Incorrect; while surfactant proteins SP-A and SP-D contribute to host defense against pathogens, this is secondary to biophysical roles.
-
(C) Prevent alveoli from collapsing by decreasing surface tension: Correct; surfactants, mainly dipalmitoylphosphatidylcholine (DPPC) from type II alveolar cells, form a film reducing surface tension per the Law of Laplace, preventing atelectasis.
-
(D) Aid in carbon dioxide exchange: Incorrect; gas exchange (O2/CO2) relies on diffusion across alveolar-capillary membranes, not directly on surfactants.
Surfactant Composition
Pulmonary surfactant consists of 90% lipids (primarily DPPC) and 10% proteins (SP-A, SP-B, SP-C, SP-D). SP-B and SP-C enable low surface tension, while SP-A/SP-D aid immunity. Deficiency causes neonatal respiratory distress syndrome (RDS).
Clinical Relevance
In premature infants, surfactant therapy restores function, reducing RDS mortality. It lowers breathing work by increasing compliance. For CSIR NET, note biophysical primacy over immunological roles.
