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Question 358
Physiology → Haematology
Classification
Question
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A large agranular leucocyte with abundant cytoplasm and a kidney-shaped nucleus is identified in peripheral blood.
Question Stem
Which subsequent event is most characteristic of this cell?
Options
A
After several days in the circulation it migrates into tissues and becomes a macrophage.
B
It remains permanently intravascular and differentiates into a neutrophil.
C
It becomes a platelet after losing its nucleus.
D
It develops eosinophilic granules and becomes the principal circulating granulocyte.
E
It differentiates into an erythrocyte after approximately 72 hours.
Explanation
Monocytes are the largest leucocytes and may have a kidney-, bean- or horseshoe-shaped nucleus with abundant clear cytoplasm. After 4–6 days in the circulation, monocytes migrate out into tissues and become tissue macrophages.
Option Validity
B) Monocytes migrate out of the circulation and become tissue macrophages rather than differentiating into neutrophils.
C) Platelets are membrane-encapsulated fragments of megakaryocytes and are not derived from circulating monocytes.
D) Eosinophils are a separate granulocyte lineage; monocytes do not acquire eosinophilic granules to become eosinophils.
E) Monocytes do not differentiate into erythrocytes; their characteristic tissue fate is macrophage differentiation.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Monocytes, pp.69–70.