CHAPTER 8
Blood and Hemopoiesis
135
Erythropoiesis
Figure 8-10A
Proerythroblasts
Figure 8-10B
Basophilic Erythroblasts
Figure 8-10C
Polychromatophilic Erythroblasts
Figure 8-11A
Orthochromatophilic Erythroblasts
Figure 8-11B
Reticulocytes
Figure 8-11C
Clinical Correlation: Reticulocytosis
Thrombopoiesis
Figure 8-12A
Promegakaryocytes
Figure 8-12B
Megakaryocytes
Figure 8-12C
Clinical Correlation: Essential Thrombocytosis
Granulocytopoiesis
Figure 8-13A
A Representation of Granulocytopoiesis
Figure 8-13B
Overview of Stages of Granulocytes in Development
Figure 8-14A–C
Promyelocytes, Myelocytes, and Metamyelocytes
Figure 8-15A–C
Stab (Band) Cells, Bone Marrow Cells, and Bone Marrow
Figure 8-16
Developing Blood Cells in the Hematopoietic Compartment
Synopsis 8-2
Hematopoiesis
Synopsis 8-3
Pathological and Clinical Terms for Mature and Developing Blood Cells
Peripheral Blood Cells
Introduction and Key Concepts for
Peripheral Blood Cells
Blood smears are prepared so that the morphology of the
formed elements can be assessed and the relative numbers of
the leukocytes can be calculated (
differential leukocyte count
).
If a person is anemic, examination of erythrocyte morphology
can help classify the type of anemia. If a person has an elevated
leukocyte count, a
differential white cell count
can provide
valuable information toward determining what kind of infec-
tion or leukemia the person has. All formed elements serve criti-
cally important functions.
Erythrocytes
function in transport of
respiratory gases,
platelets
function mainly in hemostasis, and
leukocytes
function in various ways to protect from infection
by a wide variety of potential pathogenic organisms.
ERYTHROCYTES
deliver oxygen from the lungs to all the
tissues of the body, although they are also involved in carbon
dioxide transport and pH regulation. Because erythrocytes
are anucleate and lack membrane-bounded organelles, their
internal structure is homogeneous. An erythrocyte is essen-
tially a plasmalemma bag containing a highly concentrated
(30%) hemoglobin solution. In addition, erythrocytes have a
membrane-associated complex of cytoskeletal proteins that ren-
ders the biconcave disk shape (Figs. 8-2A to 8-3B).
PLATELETS
(
thrombocytes
) are small fragments of cytoplasm
with a complex and highly organized structure. They normally
range in number from 200,000 to 400,000/
μ
L. If the plate-
let number falls below 60,000/
μ
L (“thrombocytopenia”), the
integrity of the smallest blood vessels is compromised.
Platelets
function to minimize loss of blood when there is a breach in the
circulatory system (Fig. 8-2B).
LEUKOCYTES
are much less abundant than erythrocytes,
4,500 to 11,000/
μ
L in contrast to about 5 million/
μ
L. How-
ever, white cell numbers can increase markedly in some cir-
cumstances, such as infection or leukemia. Leukocytes have a
wide range of life spans—from a few days (neutrophils) to years
(some lymphocytes). All leukocytes are involved in defense
against microorganisms and other foreign agents and in tissue
responses to injury. Usually, they perform their functions only
after leaving the blood stream and entering the conventional
connective tissue through processes of attachment to endothe-
lial cells and active movement through gaps in the endothe-
lium (
diapedesis
). Leukocytes are constantly released from the
bone marrow to be delivered by the cardiovascular system to
the vascular beds of all peripheral tissues. Leukocytes are clas-
si± ed as either
nongranular
(
agranular
) or
granular
depending
on whether speci±
c cytoplasmic granules are evident when the
cells are stained with Romanowsky-type stains like Wright
stain. The three types of
granulocytes
basophils
,
eosinophils
,
and
neutrophils
—are named and identi±
ed by the staining reac-
tion of their speci±
c granules. The two types of
nongranular
leukocytes
,
lymphocytes
and
monocytes
, also have granules,
but the granules are only nonspeci±
c granules (
lysosomes
). All
granulocytes are
terminal cells
; that is, they will never again
divide because they have lost that capacity during differentia-
tion. Monocytes and lymphocytes have the potential for further
division.
Lymphocytes
are the second most abundant leukocyte,
amounting to about 25% to 33% of leukocytes. These are the
cells that mediate speci±
c immunity against foreign molecules
and organisms.
B lymphocytes
produce immunoglobulins, and
their derivatives,
plasma cells
, are specialized to secrete solu-
ble antibodies.
T lymphocytes
are the agents of cell- mediated
speci±
c immune responses, and they comprise several types.
Among these,
cytotoxic T cells
function to kill virus-infected
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