Webster's New World Medical Dictionary

jaundice, physiologic
See 
physiologic jaundice.
jaw
The movable junction of the bones below the
mouth (the mandible) and the bone just above
the mouth (the maxilla).
JC virus
A virus that commonly causes infections
of no consequence in children with a normal
immune system, but which is responsible for an
infection of the brain and spinal cord called pro-
gressive multifocal leukoencephalopathy (PML) in
people with AIDS and other forms of immune sys-
tem impairment. Abbreviated JVC. The JC virus is a
human polyomavirus. It is a small virus with a
closed circular genome consisting of double-
stranded DNA. The letters JC are the initials of a
patient with PML from whose brain the virus was
first isolated.
jejunal
Having to do with the jejunum.
jejunostomy
A surgical operation to create an
opening of the jejunum (a part of the small intes-
tine) to a hole (stoma) in the abdomen.
jejunum
The middle portion of the small intes-
tine. The jejunum is about 2.4 meters (8 feet) in
length and located halfway between the duodenum
and the ileum. The jejunum is responsible for much
of the absorption of the fluids and calcium that we
ingest. See also 
intestine; intestine, small.
jellyfish sting
The injection into the skin of
venom from the stinging unit (nematocyst) of the
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jellyfish. The jellyfish tentacles can extend for sev-
eral feet and are lined with venom-filled cells
(nematocysts). One tentacle may fire thousands of
nematocysts into the skin on contact. The pain can
be severe, particularly in the first hours after an
attack, and itching is common. The victim may have
weakness, nausea, headache, muscle pain and
spasms, tearing and nasal discharge, increased per-
spiration, changes in pulse rate, and chest pain.
Welting may persist for weeks at the site, and scar-
ring may remain. Even dead jellyfish are capable of
leaving a painful mark. Those who get serious stings
may require oxygen or cardiorespiratory assistance.
There is no antivenom for the stings of North
American jellyfish, but there is antivenom for the
stings of some Australian species.
jet lag
A temporary disorder that features fatigue
and insomnia and that is caused when the body’s
natural rhythms are interrupted by rapid travel
across time zones. Other symptoms of jet lag
include anxiety, constipation, diarrhea, confusion,
dehydration, headache, irritability, nausea, sweat-
ing, coordination problems, and even memory loss.
See also 
circadian clock.