Question

What is the function of phospholipid molecules coating the alveolar surfaces?

1) To prevent the alveoli from collapsing
2) To facilitate gas exchange
3) To increase the surface area of the alveoli
4) To secrete surfactant

Answer 1

Phospholipid molecules in the form of surfactant prevent the alveoli from collapsing by reducing surface tension. Type II alveolar cells secrete surfactant, allowing the alveoli to function properly for gas exchange.

Step-by-step explanation:

The function of phospholipid molecules coating the alveolar surfaces is primarily to prevent the alveoli from collapsing. Surfactant, a mixture of phospholipids and lipoproteins, is released by type II alveolar cells. It significantly reduces the surface tension at the air-tissue/water interface of the alveoli. This surface tension, if not regulated, would cause the alveoli to resist expansion during inhalation and might lead to their collapse during exhalation. Thus, phospholipids are essential for maintaining open and functional alveoli, ultimately facilitating gas exchange.

During inhalation, surfactant molecules are spread thin, and surface tension increases. In contrast, during exhalation, these molecules come back together, reducing surface tension and preventing alveolar collapse. This property of surfactant is unique and crucial for normal respiration.