ileum The third and last section of the small intestine.
imaginal disk A region or cluster of cells in the lar-
vae of an insect that are undifferentiated and are deter-
mined to form specific organs or tissues during
metamorphosis to the adult stage.
imaging A medical diagnostic technique by which
useful organ images are obtained from the radiation
emitted by RADIONUCLIDEs that are introduced into
organs, or from radiation absorbed by atomic nuclei
within the organs. Typical examples are imaging
obtained by recording the radiation emitted by a
radionuclide such as 99mT c, and the^1 H-NMR imaging
obtained by whole-body NUCLEAR MAGNETIC RESO-
NANCEmeasurements.
See alsoBONE IMAGING;BRAIN IMAGING;MAGNET-
IC RESONANCE IMAGING.
immigration The moving into a location in which
the individual is not a native of the area.
See alsoEMIGRATION.
immune response The process by which the body
of an organism recognizes and fights invasion of
microorganisms, viruses, and other substances (anti-
gens) that may be harmful to the body; the total time
from recognition of the intrusion to attack or tolerance
of the antigen.immunoglobulin(Ig) Also known as antibodies,
these are proteins created by plasma cells and B cells
that are designed to control the body’s immune
response by binding to antigens. There are more than
1,000 possible antibody variations and five major
types, and each is specific to a particular antigen. Of
the five main types—IgA, IgD, IgE, IgG, and IgM—the
most common are IgA, IgG, and IgM.
See alsoANTIBODY.immunogold A method for visualizing proteins in
electron microscopy within a cell using gold particles
attached to an ANTIBODYthat binds specifically to that
protein.imperfect fungi Fungi (deuteromycetes) that
do not have sexually produced spores as part
of their life cycle. They cause skin diseases in
humans and include the organisms causing ring-
wormand athlete’s foot.impotence(erectile dysfunction) Refers to a man’s
inability to achieve or maintain an erection suitable
enough to complete sexual intercourse.173