blood back to the body after the cell separator has
extracted the appropriate blood product. The
entire process takes about two hours for most
blood products. Some people find insertion of the
needles uncomfortable and may also have chills
and mild discomforts during the hemapheresis or
for a short time afterward. There are relatively few
risks with hemapheresis.
KINDS OF HEMAPHERESIScytapheresis = removal of cells
leukapheresis = removal of leukocytes (white blood cells)
plasmapheresis = removal of plasma
plateletapheresis = removal of platelets
See also BLOOD DONATION; HEMOCHROMATOSIS;
PHLEBOTOMY.
hematoma Bleeding into the tissues that forms a
contained mass. Most superficial hematomas are
benign, such as the common hematoma auris,
involving the auricle (outer EAR) and BLACK EYE,
involving the orbital tissues surrounding the EYE.
Such hematomas typically occur as the conse-
quence of blows to the tissues that cause BLOOD
vessels to break. As the blood coagulates the mass
hardens. A hematoma may take weeks to several
months to fully resolve as the body works to dis-
mantle the clot. Most superficial hematomas do
not require medical care, though a doctor should
evaluate any injury that potentially involves the
eye or symptoms of HEARING LOSS.
An internal hematoma that occurs within the
skull (subdural or subarachnoid hematoma) is
particularly dangerous and even life-threatening
because it causes increased pressure that damages
the BRAIN. Hematomas that occur within major
organs such as the LIVERor the SPLEENare also seri-
ous. These hematomas may be the result of
trauma or may occur because of anomalous blood
vessel structures (such as hemangioma) that spon-
taneously rupture. Internal hematomas require
medical evaluation and careful monitoring. The
doctor may recommend surgical removal of
hematomas that threaten the function of vital
organs such as the brain or the liver.
See also BRAIN HEMORRHAGE; ECCHYMOSIS;
PETECHIAE; PURPURA; STROKE; TRAUMATIC BRAIN INJURY
(TBI).
hemoglobin A combined protein within ery-
throcytes (red BLOODcells) that is crucial to the
OXYGEN–CARBON DIOXIDE EXCHANGE. Two proteins
come together to form hemoglobin: heme, a red-
dish pigment that contains iron, and globin.
Hemoglobin bonds loosely with oxygen and car-
bon dioxide molecules, depending on which is in
higher concentration.
In the LUNGS, oxygen molecules have the higher
concentration and bind with the hemoglobin. As
the blood carries the erythrocytes deeper into the
body where oxygen concentrations are lower, the
bond becomes less stable. When the erythrocytes
reach the CAPILLARY BEDSwhere the concentration
of carbon dioxide is higher than the concentration
of oxygen, the hemoglobin releases its oxygen
molecules and replaces them with carbon dioxide
molecules and carries the carbon dioxide back to
the lungs where the exchange repeats.Cigarette smoke contains high levels of
carbon monoxide. Heavy smokers may
have blood concentrations of carbon
monoxide of 7 to 9 percent.Carbon monoxide binds more strongly with
hemoglobin than oxygen or carbon dioxide, form-
ing a tight bond (the compound carboxyhemoglo-
bin) that blocks hemoglobin from binding with
either. Only small amounts of carbon monoxide
inhaled into the lungs can interfere with the oxy-
gen–carbon dioxide exchange significantly enough
to cause poisoning (HYPOXIA) or death. Carbon
monoxide begins to cause symptoms of oxygen
deprivation when its blood concentration reaches
10 percent, impairs neurologic function at 30 per-
cent, and can cause death at 50 percent. A gas
commonly present in the environment, carbon
monoxide is a byproduct of incomplete combus-
tion.
See also ANEMIA; HEMOCHROMATOSIS; INHALED TOX-
INS; SICKLE CELL DISEASE; SMOKING AND HEALTH; THA-
LASSEMIA.hemolysis The destruction and disassembly of
erythrocytes (red BLOODcells). Erythrocytes live in
the blood for about 120 days after their release
from the BONE MARROW. At the end of this time
they either die or the SPLEENculls them from circu-142 The Blood and Lymph