What does a mixture of surfactants contain?

RRB Nsg. Superintendent-20 July 2019 (Shift-1)

Biochemistry and Nutrition

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-1)

Explanation

Pulmonary surfactant is a lipoprotein complex, which by definition is composed of lipids and proteins.
The lipid component makes up about 90% of surfactant, with dipalmitoylphosphatidylcholine (DPPC) being the most abundant. Its primary role is to reduce surface tension in the alveoli.
The protein component constitutes the remaining 10% and includes specific surfactant proteins (SP-A, SP-B, SP-C, SP-D) that are essential for the structure, function, and immune properties of the surfactant layer.

Option B: Mucus is produced by goblet cells in the upper airways to trap debris, not by Type II alveolar cells that produce surfactant. Chloride is an electrolyte involved in fluid transport, not a primary structural component of the surfactant molecule.
Option C: While protein is a correct component, chloride is not. Chloride is an ion found in bodily fluids but does not form the structural backbone of the surfactant complex.
Option D: Although lipid is the major component, the other crucial structural part is protein, not the chloride ion.

Visual 1: Diagram - An illustration of a lung alveolus showing Type II pneumocytes secreting surfactant onto the alveolar surface. The diagram should show how the surfactant molecules intersperse between water molecules to reduce surface tension and prevent alveolar collapse.
Visual 2: Chart - A pie chart detailing the composition of pulmonary surfactant, with a large slice for Lipids (90%) broken down into DPPC and other phospholipids, and a smaller slice for Proteins (10%) labeled with SP-A, B, C, D.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Composition of Pulmonary Surfactant as background academic context rather than a clinical decision trigger.
A deficiency of pulmonary surfactant in premature infants is the primary cause of Neonatal Respiratory Distress Syndrome (NRDS). Without sufficient surfactant, the alveoli collapse upon exhalation, leading to severe breathing difficulty.
The treatment for NRDS involves administering exogenous surfactant (derived from animal sources or synthesized) directly into the infant's lungs via an endotracheal tube.
What if? - If a full-term infant develops Acute Respiratory Distress Syndrome (ARDS) from a severe infection, their existing surfactant can be inactivated by inflammatory debris. This functional deficiency also leads to alveolar collapse and may require mechanical ventilation and, in some cases, surfactant replacement therapy.

How to Approach the Question

This is a factual recall question testing your knowledge of the biochemical composition of a specific physiological substance.
Identify the key term in the question: 'surfactants'. Specifically, this refers to pulmonary surfactant.
Recall the basic nature of surfactant. It is known as a 'lipoprotein' complex.
Break down the term 'lipoprotein': 'lipo-' refers to lipids (fats), and 'protein' refers to proteins.
Evaluate the given options. The option 'Protein and lipid' directly matches the definition of a lipoprotein.
Eliminate the other options. 'Mucus' has a different function and origin in the airways. 'Chloride' is an electrolyte (an ion) and not a primary structural component of this large molecule complex.

Concept Tested & Keywords

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