Topics:
Animal Physiology, Animal Refresher
Correct Sequence of RBC Formation (Erythropoiesis)
The correct sequence of RBC formation (erythropoiesis) is:
- Rubriblast → Prorubricyte → Rubricyte → Metarubricyte → Reticulocyte → RBC — Correct Answer
- Rubriblast → Prorubricyte → Metarubricyte → Rubricyte → Reticulocyte → RBC
- Reticulocyte → Rubricyte → Prorubricyte → Metarubricyte → Rubriblast → RBC
- Reticulocyte → Rubricyte → Prorubricyte → Rubricyte → Metarubriblast → RBC
Explanation:
Correct Answer: Rubriblast → Prorubricyte → Rubricyte → Metarubricyte → Reticulocyte → RBC
Erythropoiesis (RBC formation) follows a precise maturation sequence in the bone marrow, starting from the most immature blast cell and progressing to the mature anucleate RBC:
Erythropoiesis Steps
- Rubriblast (Pronormoblast): Earliest committed erythroid precursor; large nucleus, basophilic cytoplasm.
- Prorubricyte (Basophilic normoblast): Begins hemoglobin synthesis; deeply basophilic cytoplasm.
- Rubricyte (Polychromatic normoblast): Hemoglobin accumulates; cytoplasm becomes polychromatic (mix of blue and pink).
- Metarubricyte (Orthochromatic normoblast): Last nucleated stage; nucleus becomes pyknotic (shrunken, dark); cytoplasm mostly eosinophilic.
- Reticulocyte: Nucleus extruded; cell still contains residual RNA (detected with supravital staining); released from bone marrow into blood.
- RBC (Mature erythrocyte): Fully mature, biconcave, anucleate, filled with hemoglobin.
Key Facts
- Principal erythroid growth factor: Erythropoietin (secreted by kidney).
- Maturation factors for RBC: Vitamin B12, Folic acid, Intrinsic factor (Castle's factor).
- Reticulocyte count is a clinical indicator of bone marrow activity.
Why Other Options Are Wrong
- Option B → Wrong order: Metarubricyte comes AFTER Rubricyte, not before.
- Option C & D → These sequences are entirely reversed — erythropoiesis proceeds from blast to mature cell, not in reverse.
