What is normally the largest mature blood cell in the peripheral blood of domestic species?

• A. Eosinophil
• B. Lymphocyte
• C. Monocyte
• D. Neutrophil

Answer: (C)

Monocytes are the largest mature white blood cells circulating in peripheral blood across domestic species. They typically exceed the size of neutrophils, eosinophils, and lymphocytes, measuring roughly 12–20 μm in diameter. Their large size is paired with a prominent, often kidney-shaped nucleus and ample gray-blue cytoplasm, which makes them stand out on a blood smear. Functionally, they circulate briefly and then migrate into tissues to become macrophages, where they perform phagocytosis and antigen presentation. In contrast, lymphocytes are usually smaller with a round, dense nucleus, neutrophils have a segmented nucleus and granulated cytoplasm, and eosinophils contain visible granules; these features help explain why monocytes are the largest mature blood cell among the options.