USMLE Step 1 Question 340

Question:

Which of the following cells are responsible for producing a substance that reduces surface tension in the alveoli?

Correct Answer: E.  Type II pneumocytes

Type II pneumocytes are responsible for producing surfactant, which reduces surface tension in the alveoli and prevents collapse of the lung.
(D) Type I pneumocytes are thin cells that comprise 97% of the alveolar lining. Their primary purpose is gas exchange. (A) Clara cells lack cilia and secrete glycosaminoglycans that are thought to protect the bronchiolar mucosa. (B) Macrophages and (C) smooth muscle cells do not secrete surfactant.