Webster's New World Medical Dictionary

abducens nerve
See 
abducent nerve.
abducent nerve
The sixth cranial nerve, which
emerges from the skull to operate the lateral rectus
muscle. This muscle draws the eye toward the side
of the head. Paralysis of the abducent nerve causes
inward turning of the eye.
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abduction
The movement of a limb away from
the midline of the body. The opposite of abduction
is adduction.
abductor muscle
See 
muscle, abductor.
ABG
Arterial blood gas, a sampling of the blood
levels of oxygen and carbon dioxide within the
arteries, as opposed to the levels of oxygen and car-
bon dioxide in veins. Typically, the acidity (pH) is
also simultaneously measured.
abiotrophy
Loss of function, or degeneration for
reasons unknown.
ablate
To remove, from a Latin word meaning “to
carry away.” See 
ablation.
ablation
Removal or excision. Ablation is usually
carried out surgically. For example, surgical
removal of the thyroid gland (a total thyroidectomy)
is ablation of the thyroid.
abnormal
Outside the expected norm, or
uncharacteristic of a particular patient.
ABO blood group
The major human blood
group system. The ABO type of a person depends on
the presence or absence of two genes, A and B.
These genes determine the configuration of the red
blood cell surface. A person who has two A genes
has red blood cells of type A. A person who has two
B genes has red cells of type B. If the person has one
A and one B gene, the red cells are type AB. If the
person has neither the A nor the B gene, the red
cells are type O. It is essential to match the ABO sta-
tus of both donor and recipient in blood transfu-
sions and organ transplants.