What Substance Do the Secretory Cells in the Lung Release

Question

What substance do the secretory cells in the lung release?  
A) Carbon dioxide
B) Myoglobin
C) Oxyhemoglobin
D) Surfactant
E) Carbonic anhydrase

Accepted Answer

The secretory cells in the lung release surfactant, which is a substance that helps to reduce surface tension in the alveoli and prevent their collapse during exhalation. Carbon dioxide is not released by secretory cells but is produced during the process of cellular respiration. Myoglobin and oxyhemoglobin are proteins involved in oxygen transport in the blood, but are not released by the lung secretory cells. Carbonic anhydrase is an enzyme that catalyzes the interconversion of carbon dioxide and water, but is also not released by lung secretory cells.