Kaplan USMLE Step 1: Diagnosis on a section of resected lung

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

A 19-year-old man is brought to the emergency department because of a gunshot wound to the chest. An emergency thoracotomy is performed and, in order to stop the bleeding, a segment of the lung is removed. A photomicrograph of a section of resected lung is shown. Which of the following products is produced by the cells indicated by the arrows? 

A. Alkaline phosphatase 

B. Angiotensin-converting enzyme 

C. Immunoglobulin

D. Major basic protein 

E. Mucus 

F. Surfactant 

G. Tubular myelin

The correct answer is F.

Surfactant is produced by type II pneumocytes. These cells are cuboidal with round nuclei and a foamy cytoplasm, exemplified by the cells marked by the arrows on this photomicrograph.

Choice A. The biopsy sample from this patient is from the lung, and the arrows are pointing to type II pneumocytes, which produce surfactant. Alkaline phosphatase is produced by osteoblasts in bone.