outer layer; muscular middle layer; and
inner watertight layer. Each ureter is sup-
plied by blood vessels and nerves. Urine
flows down the ureters partly from grav-
ity but mainly as a result of peristalsis.
Some people are born with double
ureters, on 1 or both sides of the body.
This sometimes causes refluxof urine,
incontinence, or infection.
ureteric colicSee renal colic.
ureterolithotomyThe surgical removal
of a stone (see calculus, urinary tract)
stuck in a ureter. It is not commonly
needed because lithotripsyand cysto-
scopycan be used to deal with stones.
urethraThe tube through which urineis
excreted from the bladder. In females, it
is short and opens to the outside in
front of the vagina. In males, it is much
longer, is surrounded by the prostate
gland at its upper end, and forms a
channel through the length of the penis.
urethral dilatationThe procedure in
which a urethral stricturein a male is
widened by inserting a slim, round-
tipped instrument through the opening
of the urethraat the tip of the penis.
urethral dischargeA fluid that flows
from the urethrain some cases of ure-
thritiscaused by infection.
urethral strictureA rare condition in
which the male urethrabecomes nar-
rowed and sometimes shortened as a
result of shrinkage of scar tissue within
its walls. Scar tissue may form after
injury to the urethra or after persistent
urethritis. The stricture may make passing
urine or ejaculation difficult or painful,
and it may cause some deformation of
the penis when erect. Treatment is usu-
ally by urethral dilatation.
urethral syndrome, acuteA set of
symptoms, usually affecting women,
that are very similar to cystitisbut which
occur in the absence of infection.
urethritisInflammation of the urethra,
usually due to an infection but some-
times having other causes.
Urethritis may be caused by various
infectious organisms, including the bac-
terium that causes gonorrhoea. Non-
gonococcal urethritismay be caused by
any of a large number of different types
of microorganisms. Urethritis may also
be caused by damage from an accidentUmbilical hernias sometimes develop
in adults, especially in women after
childbirth. Surgery may be necessary for
a large, persistent, or disfiguring hernia.
umbilicusThe scar on the abdomen
that marks the site of attachment of the
umbilical cordto the fetus. It is com-
monly called the navel.
unconsciousA specific part of the mind
in which ideas, memories, perceptions,
or feelings that a person is not currently
aware of are stored and processed. The
contents of the unconscious mind are
not easily retrieved, in contrast to those
of the subconscious. (See also Freudian
theory; Jungian theory.)
unconsciousnessAn abnormal loss of
awareness of self and one’s surroundings
due to a reduced level of activity in the
reticular formation of the brainstem. An
unconscious person can be roused only
with difficulty or not at all. Unconscious-
ness may be brief and light, as in fainting,
or deep and prolonged (see coma).
underbiteSee prognathism.
unsaturated fatsSee fats and oils.
unstable bladderAnother name for
irritable bladder.
uraemiaThe presence of excess urea
and other chemical waste products in
the blood, caused by kidney failure.
uraniumA radioactive metallic element
that does not occur naturally in its pure
form but is widely found in ores such as
pitchblende, carnotite, and uraninite.
Radioactive decay of uranium yields a
series of radioactive products, including
radiumand radon. During the various
decay stages, radiationis emitted. Ura-
nium is also poisonous.
ureaA waste product of the breakdown
of proteins by the liver that is transpor-
ted to the kidneys and eliminated in the
urine. Urea is also formed in the body
from the breakdown of cell proteins. Kid-
ney failureimpairs the kidneys’ ability
to eliminate urea and leads to uraemia;
measurement of blood levels of urea is a
routine kidney function test. Urea is
used in various creams and ointments
to treat skin disorders such as psoriasis.
ureterOne of the 2 tubes that carry urine
from the kidneysto the bladder. Each
ureter is 25–30 cm long. There are 3 lay-
ers in the walls of the ureters: a fibrous
UMBILICUS URETHRITIS
U