Webster's New World Medical Dictionary

loin
The portion of the lower back from just
below the ribs to the pelvis.
long arm of a chromosome
See 
chromosome.
long QT syndrome
A disorder of the heart’s
electrical system that predisposes individuals to
irregular heartbeats, fainting spells, and sudden
death. The irregular heartbeats are typically brought
on by stress or vigorous activity. Abbreviated LQTS.
LQTS is often symptomless and undiagnosed, but it
is well known as a cause of sudden cardiac death in
young, apparently healthy people, most notably
competitive athletes. QT refers to an interval seen in
an electrocardiogram (EKG) test of heart function.
There are multiple genetic forms of LQTS. Romano-
Ward syndrome is an autosomal dominant form of
LQTS. The Jervell and Lange-Nielsen syndrome is an
autosomal recessive form of LQTS and is character-
ized by congenital profound bilateral sensorineural
hearing loss and long QT interval.
long-chain-3-hydroxyacyl-CoA dehydroge-
nease deficiency
See 
deficiency, LCHAD.
longevity
Lifespan. Increased longevity means a
longer life.
longitudinal
Along the length of something; run-
ning lengthwise or, by extension, over the course of
time.
longitudinal section
A section that is cut along
the long axis of a structure. Longitudinal section is
the opposite of cross-section.
longitudinal study
A study done over the pas-
sage of time. For example, a longitudinal study of
children with Down syndrome might involve the
study of 100 children with this condition from birth
to 10 years of age. Longitudinal study is the opposite
of cross-sectional (synchronic) study. Also known
as diachronic study.
lordosis
Inward curvature of the spine. The
spine is not supposed to be absolutely straight, so
some degree of curvature is normal. When the curve
exceeds the usual range, it may be due to muscu-
loskeletal disease or simply to poor posture.
Treatment usually involves physical therapy,
although in severe cases surgery, casting, and/or
bracing may be required. The neck and low back
normally have some lordosis.