Encyclopedia of Health and Medicine

U
uremia A serious condition in which nitrogenbased
toxins such as urea and creatinine, the primary
waste products of METABOLISM, accumulate in
the BLOOD because the KIDNEYS are unable to filter
them out and pass them from the body via the
URINE. Uremia indicates RENAL FAILURE. Urologists
sometimes use the term azotemia to designate
preclinical uremia—that is, rising levels of urea in
the blood that have not yet reached a level at
which they cause symptoms.
Symptoms of uremia include
• NAUSEA and VOMITING
• confusion
• HEADACHE
• loss of APPETITE
• lethargy and difficulty concentrating
Blood and urine tests to measure levels of
blood urea nitrogen (BUN) and creatinine confirm
the diagnosis. Treatment is generally RENAL DIALYSIS
to filter metabolic wastes and toxins from the
blood, to restore the body’s electrolyte, chemical,
and water balances. KIDNEY TRANSPLANTATION may
be a viable treatment option when kidney failure
becomes permanent, such as in END-STAGE RENAL
DISEASE (ESRD).
See also NEPHROPATHY; NEPHROTOXINS.
ureter A tubular structure that carries URINE from
the kidney to the BLADDER. Urine from the kidney’s
collecting tubules drains into the renal pelvis,
which channels the urine into the ureter. The
ureter exits the kidney at the hilus and parallels the
inferior VENA CAVA (left ureter) or the AORTA (right
ureter) through the abdomen to the pelvis. At the
pelvis the ureter crosses over the respective iliac
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branches (ARTERY and VEIN) and enters the top back
of the bladder. The ureter forms a short, flattened
tunnel within the bladder wall before opening into
the interior of the bladder. This tunnel functions as
a valve to help keep urine from flowing back up the
ureter from the bladder. Each ureter is about 12
inches long, though the left is slightly longer than
the right as the left kidney sits about an inch higher
in the abdomen. The structure of the ureters is the
same in men and women.
A smooth epithelial membrane forms the inner
lining of the ureter. Two layers of MUSCLE surround
the ureteral epithelium, the first running more or
less lengthwise (longitudinal) though spiraling
widely around the epithelium, and the second
wrapping around the ureter in a circular pattern.
The outer layer of the ureter is fibrous tissue. The
muscle layers of the ureter contract in rhythmic
waves (PERISTALSIS) to move urine from the kidneys
to the bladder. The ureter is fairly thick and rigid,
with an inner diameter of only 3 or 4 millimeters.
For further discussion of the ureters within the
context of the urinary system’s structure and
function please see the overview section “The Urinary
System.”
See also GLOMERULUS; KIDNEYS; NEPHRON; URETHRA;
VESICOURETERAL REFLUX.
urethra A narrow, somewhat muscular tube that
carries URINE from the BLADDER to the outside of the
body. The point of exit is the urinary or urethral
meatus. The urethral sphincter MUSCLE at the base
of the bladder controls the release of urine into the
urethra. Once the urethral sphincter relaxes to let
urine pass, the urine flows to the outside of the
body until the bladder empties and the urethral
sphincter tightens. It may take a few seconds after
the sphincter closes for the residual urine in the