Page 31 - Essential Haematology

Chapter 2 Erythropoiesis and anaemia / 17

Pronormoblast

Early

BONE
MARROW

Intermediate
(polychromatic)

Late
(pyknotic)

Reticulocytes

BLOOD
Red cells

Figure 2.2 The amplifi cation and maturation sequence in the development of mature red cells from

the pronormoblast.

pronormoblast usually gives rise to 16 mature red
cells (Fig. 2.2 ). Nucleated red cells (normoblasts)
Normoblast Reticulocyte Mature are not present in normal human peripheral blood.
RBC

They appear in the blood if erythropoiesis is occur-
ring outside the marrow (extramedullary erythro-
poiesis) and also with some marrow diseases.

Erythropoietin
Nuclear DNA Yes No No
Erythropoiesis is regulated by the hormone eryth-
RNA in cytoplasm Yes Yes No
ropoietin. Erythropoietin is a heavily glycosylated
polypeptide of 165 amino acids with a molecular
In marrow Yes Yes Yes
weight of 34 kDa. Normally, 90% of the hormone
In blood No Yes Yes is produced in the peritubular interstitial cells of the
kidney and 10% in the liver and elsewhere. Th ere
are no preformed stores and the stimulus to eryth-
Figure 2.3 Comparison of the DNA and RNA content,

and marrow and peripheral blood distribution, of the ropoietin production is the oxygen (O 2 ) tension in
erythroblast (normoblast), reticulocyte and mature red the tissues of the kidney (Fig. 2.4 ). Hypoxia induces
blood cell (RBC). hypoxia - inducible factors (HIF - 2 α and β ) which