Blood Cells Are Created in the Red Bone Marrow
LEARNING OBJECTIVES
1.
Outline
the events in the life span of a red
blood cell.
2.
Describe
the life span of a white blood cell.
3.
identify
the steps in the formation and destruc-
tion of red blood cells.
4.
Explain
how red blood cell formation is regulated.
s you learned in Chapter 5, blood cells are
formed in red bone marrow. They travel
throughout the body via large arteries and
veins and narrow arterioles, capillaries, and
venules. As they move through these vessels, they bend,
stretch, twist, get compressed, and collide with each other
and with the vessel walls, experiencing quite a bit of wear
and tear along the way. As a result, RBCs last only about
120 days. In contrast, most WBCs last only a few days be-
cause they eventually engulf enough foreign bacteria and
cell debris to interfere with their own life functions. In
times of severe infection, WBCs may last only a few hours.
In contrast, some types of lymphocytes that provide im-
munity can last for years.
All the Formed Elements Develop
from Red Bone Marrow Stem Cells
The
process
of making
formed
elements of blood is called
hemo-
poiesis
, or
hem atopoiesis
(hem'-a-to-
poy-E-sis). Before birth, hemopoi-
esis first occurs in the yolk sac of the embryo and then in
the liver, thymus, and lymph nodes. Eventually the process is
moved to red bone marrow, starting about 3 months before
birth through the end of life. In response to hormones,
plu-
ripotent stem cells
(0.05-0.1% of red bone marrow cells)
differentiate into two other types,
lymphoid stem cells
and
myeloid stem cells
. These stem cells further differentiate
into the formed elements (
Figure 10.4
).
hemopoiesis
(he-
mo-poy-E-sis) Blood
cell production.
O rigin and d e v e lo p m e n t o f b lo o d cells • Figure 10.4
The various blood cells form from stem cells in the red bone
marrow and, in some cases, lymphoid tissue through cell divi-
sion and differentiation. Some of these blood cells eventually
migrate into the tissues and receive new names (for example,
monocytes become macrophages).
Key:
Formed elements
of circulating blood
Tissue cells
Myeloid stem cells begin and end
development in red bone marrow.
Reticulocyte
I
Megakaryocyte
I
Red blood cell
(erythrocyte)
Platelets
(thrombocytes)
Eosinophil
T lymphocyte
B lymphocyte
(T cell)
(B cell)
— White blood cells —
(granular leukocytes)
J
L
V
>
7
— White blood cells —
(agranular leukocytes)
Mast cell
Macrophage
Plasma cell
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