In glands with mixed serous and mucous acini, what histologic feature indicates serous demilunes?

• A. Crescent-Shaped Serous Demilunes Cap Mucous Acini
• B. Uniform Mucinous Acini With No Serous Cells
• C. Serous Demilunes Are Round Clusters Of Mucous Cells
• D. All Acini Are Serous Secretory Units

Answer: (A)

In mixed glands, serous demilunes show up as a crescent-shaped cap of serous cells that overlay the mucous acinus. The mucous portion stains lighter because it’s mucin-rich, while the serous cells around it contain zymogen granules and stain darker. That crescent of darker, serous cells sitting on the mucous tubule is the telltale sign you’re looking at serous demilunes. If you only had uniform mucous acini, you wouldn’t see any serous demilunes. If demilunes were described as round clusters of mucous cells, that would misstate their composition and appearance. And if every acinus were serous, there would be no demilunes at all since that feature marks a mixed gland.