Webster's New World Medical Dictionary

islet of Langerhans
A group of specialized cells
in the pancreas that make and secrete hormones,
including insulin. These cells sit in groups (islets),
with several different types of cells in an islet,
including alpha cells that make glucagon, which
raises the level of glucose (sugar) in the blood; beta
cells that make insulin; and delta cells that make
somatostatin, which inhibits the release of numer-
ous other hormones in the body. Degeneration of
the insulin-producing beta cells is the main cause of
type 1 (insulin-dependent) diabetes mellitus.
isochromosome
An abnormal chromosome that
has two identical arms due to duplication of one
arm and loss of the other. Isochromosomes are
found in tumors and in some girls with Turner 
syndrome.
isodisomy
A remarkable situation in which both
chromosomes in a pair are from one parent only.
Isodisomy causes some birth defects and is sus-
pected to play a role in cancer. Also known as uni-
parental disomy.
isolate 1
In genetics, a group (for example, the
Amish) in which mating is always between members
of the group.
2
A single microbe or cell that has
been separated from the whole, or a pure culture
produced from an isolate.
3
A particular strain of
virus, bacteria, or organism taken from a patient.
isotonic solution
A solution that has the same
salt concentration as cells and blood. Isotonic solu-
tions are commonly used as intravenously infused
fluids in hospitalized patients.
isotope
A form of a chemical element that has a
different-from-normal atomic mass. Isotopes are
used in a number of medical tests because they can
produce images of tissues that can be used to detect
diseases or conditions.
itching
An uncomfortable sensation in the skin
that feels as if something is crawling on the skin and
makes the person want to scratch the affected area.
Itching is medically known as pruritis; something
that is itchy is pruritic.