528
UNIT FOUR
Dietary Factors Affecting Red Blood
Cell Production
The availability of two B-complex vitamins—vitamin B
12
and
folic acid—signiF cantly infl uences red blood cell production.
These vitamins are required for DNA synthesis, so they are
necessary for the growth and division of all cells. Cell divi-
sion is rapid in hematopoietic tissue, so this tissue is espe-
cially vulnerable to deF
ciency of either of these vitamins.
Lack of vitamin B
12
is usually due to a disorder in the stom-
ach lining rather than to a dietary deF ciency, because pari-
etal cells in the stomach secrete a substance called
intrinsic
factor
required to absorb vitamin B
12
.
Iron is required for hemoglobin synthesis. Although
much of the iron released during the decomposition of hemo-
globin is available for reuse, some iron is lost each day and
must be replaced. Only a small fraction of ingested iron is
absorbed. Iron absorption is slow, although the rate varies
with the total amount of iron in the body. When iron stores
are low, absorption rate increases, and when the tissues are
becoming saturated with iron, the rate greatly decreases.
Figure 14.7
summarizes the life cycle of a red blood cell.
Table 14.1
summarizes the dietary factors that affect red
blood cell production.
Low blood oxygen
Liver
Kidney
Erythropoietin
Red bone marrow
Increased
number of
red blood
cells
Increased
oxygen-
carrying
capacity
+
Bloodstream
Release into
bloodstream
Stimulation
Inhibition
FIGURE 14.6
Low blood oxygen causes the kidneys and liver to
release erythropoietin. Erythropoietin travels to red bone marrow and
stimulates the production of red blood cells that carry oxygen to tissues.
Red bone
marrow
Old red
blood cells
Nutrients
from food
Vitamin B
12
Folic acid
Iron
Small
intestine
Bilirubin
Bone
Blood
Liver
Globin + Heme
3
Red blood
cells produced
2
Blood transports
absorbed nutrients
1
Absorption
4
Red blood cells
circulate in
bloodstream for
about 120 days
5
Macrophage
Hemoglobin
Iron + Biliverdin
8
6
7
Bile
FIGURE 14.7
Life cycle of a red blood cell. (
1
) The small intestine absorbs essential nutrients. (
2
) Blood transports nutrients to red bone marrow.
(
3
) In the red bone marrow, red blood cells arise from the division of less-specialized progenitor cells. (
4
) Mature red blood cells are released into the
bloodstream, where they circulate for about 120 days. (
5
) Macrophages destroy old red blood cells in the liver and spleen. (
6
) Hemoglobin liberated
from red blood cells is broken down into heme and globin. (
7
) Iron from heme returns to red bone marrow and is reused. (
8
) Biliverdin and bilirubin
are excreted in bile.
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