Which white blood cell is the largest circulating leukocyte with a kidney-shaped nucleus and acts as a phagocyte?

Which white blood cell is the largest circulating leukocyte with a kidney-shaped nucleus and acts as a phagocyte?

• A. Monocytes
• B. Eosinophil
• C. Lymphocytes
• D. Platelets

Answer: (A)

Monocytes are the largest circulating white blood cells and have a kidney-shaped (horseshoe-like) nucleus. This morphology, combined with their role in phagocytosis, points to them as the main phagocytes of the bloodstream. When they migrate into tissues, they differentiate into macrophages and dendritic cells, which actively engulf bacteria, dead cells, and debris. Other options don’t fit as well: eosinophils have a bilobed nucleus and specialize more in responses to parasitic infections and allergies; lymphocytes are typically smaller with a round nucleus and are central to adaptive immunity rather than primary phagocytosis; platelets are not white blood cells at all.

Monocytes are the largest circulating white blood cells and have a kidney-shaped (horseshoe-like) nucleus. This morphology, combined with their role in phagocytosis, points to them as the main phagocytes of the bloodstream. When they migrate into tissues, they differentiate into macrophages and dendritic cells, which actively engulf bacteria, dead cells, and debris.

Other options don’t fit as well: eosinophils have a bilobed nucleus and specialize more in responses to parasitic infections and allergies; lymphocytes are typically smaller with a round nucleus and are central to adaptive immunity rather than primary phagocytosis; platelets are not white blood cells at all.