146
UNIT 2
Basic Tissues
Figure 8-9A.
A representation of erythropoiesis (red blood cell formation), bone marrow.
Wright stain,
3
1,569
Erythrocyte formation
includes several stages of cell changes during differentiation. Erythrocytes derive from
progenitor
cells
(
CFC
-
Es
)
that give rise to the F rst recognizable erythrocyte precursor, the
proerythroblast
. The proerythroblast is a large cell, which has a large
active nucleus with nucleoli. Each proerythroblast divides into two
basophilic erythroblasts
. Each basophilic erythroblast divides into
two
polychromatophilic erythroblasts
, each of which then divides to form
orthochromatophilic erythroblasts
, which do not divide.
These, in turn, differentiate into
reticulocytes
(±ig. 8-11B,C), which F nally become
erythrocytes
. There are some general tendencies
accompanying differentiation of erythrocytes: (1) the overall size of the cells decreases, (2) the nucleus size decreases and the condensa-
tion of the chromatin increases, (3) nucleoli disappear, and (4) the color of the cytoplasm changes from blue to gray to pink because
of a reduction of ribosomes and an increase of hemoglobin. When the ribosomes are diluted by cell division and the hemoglobin
concentration rises to a near mature level, the cell becomes an orthochromatophilic erythroblast (or
normoblast
). When the nucleus
is extruded and only a few organelles (polyribosomes and mitochondria) remain in the cytoplasm, the cell is called a
reticulocyte
. The
reticulocyte completes maturation and enters the blood circulation to become a
mature erythrocyte
(
red blood corpuscle
).
D. Cui
Proerythroblast
Proerythroblast
Basophilic
erythroblast
Basophilic
erythroblast
Polychromatophilic
erythroblast
Polychromatophilic
erythroblast
Erythrocytes
Erythrocytes
Orthochromatophilic
erythroblast (normoblast)
Orthochromatophilic
erythroblast
(normoblast)
Reticulocyte
A
D. Cui
Platelets
Megakaryocyte
Promegakaryocyte
Megakaryoblast
B
Figure 8-9B.
Thrombopoiesis (platelet formation process), bone marrow.
Wright stain,
3
843,
3
586, and
3
1,570 (
from left to
right
)
Platelets
are very small fragments of cells that have no nuclei. They are also called
thrombocytes
. Their differentiation from a large
cell, the
megakaryocyte
, takes place in the bone marrow.
Megakaryoblasts
are the precursor cells. They have a large, round nucleus,
undergo mitosis, and become
promegakaryocytes
. These cells have a large, round nucleus and develop through growth and a series
of endomitoses into
megakaryocytes
. A megakaryocyte has a large, multilobed nucleus with a huge amount of cytoplasm containing
numerous granules. The maturation process includes the development of a demarcation membrane system and the subdivision of
the cytoplasm to form platelets (±ig. 8-12A,B).
previous page 161 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online next page 163 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online Home Toggle text on/off