Encyclopedia of Health and Medicine

124 The Blood and Lymph
aged erythrocytes from circulation. The spleen also
becomes less effective in fighting infection, reducing
the body’s resistance.
Other changes in the body that occur with
advancing age affect the ability of the LYMPH VES-
SELS to collect fluid from the tissues and transport
it back to the bloodstream. Diminished MUSCLE
tone and reduced movement slow the flow of fluids
into and through the lymph vessels. Other
health conditions such as congestive HEART FAILURE
and kidney disease affect the body’s ability to
move fluids through the blood vessels, creating a
backlog. By about age 70, however, the body
begins to decrease the total amount of water its
tissues retain. This results in less water in the
blood and a lower blood volume, somewhat lowering
the BLOOD PRESSURE though increasing the
risk for blood clots (thrombosis).
See also AGING, CARDIOVASCULAR CHANGES THAT
OCCUR WITH; AGING, PULMONARY CHANGES THAT OCCUR
WITH; CANCER RISK FACTORS; SENESCENCE.
albumin The most abundant protein in PLASMA.
Albumin transports various molecules through the
BLOOD and helps sustain the blood’s oncotic pressure,
keeping fluid from seeping into the tissues.
Albumin molecules are larger than the molecules
it transports, allowing those substances, such as
electrolytes and hormones, to pass through the
walls of the blood vessels while the albumin molecules
remain within the blood vessels. Albumin is
among the numerous plasma proteins the LIVER
produces. Albumin is also available as a blood
product for transfusion. Blood banks obtain it by
separating it, using a cell separator, from donated
whole blood or plasma.
The blood of a healthy adult contains 3.5 to 5.0
grams per deciliter (g/dL) of albumin, which
makes up about 2 percent of the blood’s total volume.
A low serum albumin level (hypoalbuminemia,
decreased concentration of albumin in the
blood) often indicates liver disease such as CIRRHO-
SIS or kidney disease such as GLOMERULONEPHRITIS.
Hypoalbuminemia also occurs with serious BURNS.
An elevated albumin level (hyperalbuminemia,
increased concentration of albumin in the blood)
occurs less commonly and often signals extended
DEHYDRATION or DIABETES INSIPIDUS, a disorder of the
ADRENAL GLANDS.
See also AGING, CHANGES IN THE BLOOD AND LYMPH
THAT OCCUR WITH; BLOOD PRESSURE; BLOOD TRANSFU-
SION.
anemia A reduced ability of the BLOOD to meet
the body’s oxygenation needs arising from either a
diminished volume of erythrocytes (red blood
cells) in the blood or from reduced HEMOGLOBIN
content in the erythrocytes. Though the common
perception of anemia is that it is itself a health
condition, doctors consider anemia an indication
of other health conditions. Diagnosis and treatment
target those underlying conditions. Anemia
affects about 3.5 million people in the United
States. Anemia can affect people of any age
though is most common among menstruating
women and during PREGNANCY.
Causes of Anemia
Anemia may be acute (come on suddenly) or
chronic (continue over an extended time). Anemia
may also result from medication interactions
or ADVERSE
REACTIONS, CHEMOTHERAPY, RADIATION
THERAPY, and numerous health conditions. In general,
anemia results from three circumstances,
individually or in combination:
• excessive blood loss drains erythrocytes from
the body
• the SPLEEN destroys (hemolyzes) too many erythrocytes
• the BONE MARROW produces too few defective
erythrocytes
Blood loss Blood loss, either in large quantity
suddenly or through chronic bleeding, has a
twofold consequence on the blood’s ability to
carry oxygen. First, the bleeding reduces the
number of erythrocytes in the blood, making
fewer erythrocytes and thus less hemoglobin
available. Second, old erythrocytes, which the
spleen culls from the circulation to dismantle and
recycle, are a key source of ingredients such as
iron and hemoglobin for the production of new
erythrocytes. Traumatic hemorrhage, GASTROIN-
TESTINAL BLEEDING, and heavy menstrual bleeding
are among the causes of anemia related to blood
loss.