Pulmonary Capillaries · Histology

How does the diameter of a pulmonary capillary compare to the diameter of a red blood cell (RBC)?

  1. The capillary is near RBC diameter, forcing single-file passage
  2. The capillary is much larger, allowing RBCs to flow in clusters
  3. The capillary is too small for RBCs to enter under normal pressure
  4. The capillary diameter is approximately 100 micrometers
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Correct answer: The capillary is near RBC diameter, forcing single-file passage

Pulmonary capillaries typically have a diameter of 5–8 micrometers, which is similar to that of an RBC. This forcing of RBCs into a single file ensures that each cell is in close proximity to the alveolar wall for gas exchange.

Difficulty: Medium Question 4 of 20

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