Breathing properly requires the presence of what compound that affects surface tension of alveoli in the lungs?

The correct answer, surfactant, plays a crucial role in respiratory physiology by reducing surface tension within the alveoli, which are the small air sacs in the lungs. This reduction in surface tension is essential for several reasons. First, it prevents the alveoli from collapsing during exhalation, ensuring that the lungs can fully re-inflate during inhalation. Surfactant allows for easier expansion of the alveoli, facilitating gas exchange by maximizing the surface area available for oxygen and carbon dioxide to pass through.

Surfactant is a complex mixture of lipids and proteins, primarily produced by type II alveolar cells. Without sufficient levels of surfactant, individuals can experience conditions such as respiratory distress syndrome, which can occur particularly in premature infants whose lungs may not be fully developed.

In contrast, potassium, plasma, and sodium chloride do not have a direct role in modulating surface tension in the alveoli. While these compounds are important in general physiological processes, they do not serve the specific function of enabling proper breathing through the control of surface tension in the lungs.