529
CHAPTER FOURTEEN
Blood
TABLE
14.2
|
Types of Anemia
Type
Cause
Defect
Aplastic anemia
Toxic chemicals,
radiation
Damaged bone marrow
Hemolytic anemia
Toxic chemicals
Red blood cells destroyed
Iron def
ciency anemia
Dietary lack oF iron
Hemoglobin def
cient
Pernicious anemia
Inability to absorb
vitamin B
12
Excess oF immature cells
Sickle cell disease
DeFective gene
Red blood cells
abnormally shaped
Thalassemia
DeFective gene
Hemoglobin def
cient;
red blood cells short-lived
(b)
(a)
FIGURE 14.8
Red blood cells, normal and abnormal. (
a
) Light
micrograph oF normal human erythrocytes (1,000
×
). (
b
) Light
micrograph oF erythrocytes From a person with hypochromic anemia
(1,000
×
).
Vitamin C increases absorption oF iron in the digestive tract. Drinking
orange juice with a meal is a good way to boost iron intake. Drinking
tea with a meal reduces absorption oF iron because tannic acid in tea
binds the iron and prevents its absorption.
A deficiency of red blood cells or a reduction in the
amount of hemoglobin they contain results in a condition
called
anemia.
This reduces the oxygen-carrying capacity
of the blood, and the affected person may appear pale and
lack energy.
Table 14.2
describes types of anemia, and
f
g-
ure 14.8
shows normal red blood cells and those of someone
who has anemia. A pregnant woman may become anemic if
she doesn’t eat iron-rich foods, because her blood volume
increases due to fl
uid retention to accommodate the require-
ments of the fetus. This increased blood volume decreases
the hematocrit. Clinical Application 14.1 discusses another
disorder of red blood cells that affected British royalty.
In the absence oF intrinsic Factor, vitamin B
12
absorption decreases,
causing the red bone marrow to Form abnormally large, irregularly
shaped, thin-membraned Fragile cells. This condition, called
perni-
cious anemia,
can cause permanent brain damage iF not treated
promptly with vitamin B
12
injections. Taking excess Folic acid can
mask a vitamin B
12
def
ciency.
PRACTICE
12
Which vitamins are necessary For red blood cell production?
13
Why is iron required For the Formation oF red blood cells?
Destruction of Red Blood Cells
Red blood cells are elastic and fl exible, and they readily bend
as they pass through small blood vessels. With age, however,
these cells become more fragile, and may be damaged by pass-
ing through capillaries, particularly those in active muscles.
Damaged or worn red blood cells rupture as they pass
through the spleen or liver. In these organs, macrophages (see
chapter 5, p. 155) phagocytize and destroy damaged red blood
cells and their contents. Hemoglobin molecules liberated from
the red blood cells break down into their four component
polypeptide “globin” chains, each surrounding a heme group.
TABLE
14.1
|
Dietary Factors A±
ecting Red Blood Cell Production
Substance
Source
Function
Vitamin B
12
(requires intrinsic Factor For
absorption via small intestine)
Absorbed From small intestine
DNA synthesis
Iron
Absorbed From small intestine; conserved during red blood cell destruction and made
available For reuse
Hemoglobin synthesis
±olic acid
Absorbed From small intestine
DNA synthesis
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