Page 304 - Textbook of Pathology, 6th Edition

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Figure 12.5 The erythroid series. There is progressive condensation of the nuclear chromatin which is eventually extruded from the cell at the
late erythroblast stage. The cytoplasm contains progressively less RNA and more haemoglobin.

nucleus with dark nuclear chromatin. The cytoplasm is Erythropoietin
characteristically acidophilic with diffuse basophilic hue due
to the presence of large amounts of haemoglobin. Erythropoietic activity in the body is regulated by the
hormone, erythropoietin, which is produced in response to
5. RETICULOCYTE. The nucleus is finally extruded from anoxia. The principal site of erythropoietin production is the
the late erythroblast within the marrow and a reticulocyte kidney though there is evidence of its extra-renal production
results. The reticulocytes are juvenile red cells devoid of in certain unusual circumstances. Its levels are, therefore,
nuclei but contain ribosomal RNA so that they are still able lowered in chronic renal diseases, while a case of renal cell
SECTION II
to synthesise haemoglobin. A reticulocyte spends 1-2 days carcinoma may be associated with its increased production
in the marrow and circulates for 1-2 days in the peripheral and erythrocytosis. Erythropoietin acts on the marrow at the
blood before maturing in the spleen, to become a biconcave various stages of morphologically unidentifiable as well as
red cell. The reticulocytes in the peripheral blood are distin- identifiable erythroid precursors.
guished from mature red cells by slightly basophilic hue in There is an increased production of erythropoietin in
the cytoplasm similar to that of an orthochromatic various types of anaemias but in anaemia of chronic diseases
erythroblast. Reticulocytes can be counted in the laboratory (e.g. in infections and neoplastic conditions) there is no such
by vital staining with dyes such as new methylene blue or enhancement of erythropoietin. In polycythaemia rubra vera,
brilliant cresyl blue. The reticulocytes by either of these there is erythrocytosis but depressed production of
staining methods contain deep blue reticulofilamentous erythropoietin. This is because of an abnormality of the stem
material (Fig. 12.6). While erythroblasts are not normally cell class which is not under erythropoietin control.
present in human peripheral blood, reticulocytes are found Immunoassay of erythropoietin in plasma or serum can
normally in the peripheral blood. Normal range of be done by sensitive techniques (ELISA and radio-
reticulocyte count in health is 0.5-2.5% in adults and 2-6% in immunoassay) due to its quite low values; normal values
infants. Their percentage in the peripheral blood is a fairly are 10-25 U/L.
accurate reflection of erythropoietic activity. Their proportion
is increased in conditions of rapid red cell regeneration e.g. The Red Cell
after haemorrhage, haemolysis and haematopoietic response The mature erythrocytes of the human peripheral blood are
of anaemia to treatment.
non-nucleated cells and lack the usual cell organelles. The
normal human erythrocyte is a biconcave disc, 7.2 μm in
diameter, and has a thickness of 2.4 μm at the periphery and
Haematology and Lymphoreticular Tissues
1 μm in the centre. The biconcave shape renders the red cells
quite flexible so that they can pass through capillaries whose
minimum diameter is 3.5 μm. More than 90% of the weight
of erythrocyte consist of haemoglobin. The lifespan of red
cells is 120 + 30 days.

NORMAL VALUES AND RED CELL INDICES. Range of
12
normal red cell count in health is 5.5 ± 1.0 × 10 /L in men
12
and 4.8 ± 1.0 × 10 /L in women. The packed cell volume (PCV)
or haematocrit is the volume of erythrocytes per litre of whole
blood indicating the proportion of plasma and red cells and
ranges 0.47 ± 0.07 L/L (40-54%) in men and 0.42 ± 0.05 L/L
(37-47%) in women. The haemoglobin content in health is 15.5
± 2.5 g/dl (13-18 g/dl) in men and 14.0 ± 2.5 g/dl (11.5-16.5
g/dl) in women. Based on these normal values, a series of
Figure 12.6 Reticulocytes in blood as seen in blood stained by absolute values or red cell indices can be derived which have
supravital dye, new methylene blue. diagnostic importance. These are as under: