Encyclopedia of Health and Medicine

urolithiasis 227
liters of urine; maximum capacity of the bladder is
about 500 ml.
ANURIA
HEMATURIA
URINARY FREQUENCY
URINARY RETENTION
CONDITIONS OF ALTERED URINATION
See also NEUROGENIC BLADDER.
DYSURIA
NOCTURIA
URINARY INCONTINENCE
URINARY URGENCY
urine The liquid the KIDNEYS generate to pass
wastes and excess fluid from the body. The typical
adult makes and passes between 1,500 and 3,000
milliliters (1.5 to 3 liters) of urine every 24 hours.
Numerous variables influence the volume and
composition or urine, though in general urine is
95 percent water and 5 percent suspended or dissolved
solids.
Most of the solids urine contains are organic
wastes in the forms of urea, uric acid, creatinine,
and ammonia. These are the nitrogen-based waste
byproducts of METABOLISM that the kidneys filter
from the BLOOD. The urine also contains minerals
(electrolytes) the kidneys excrete to maintain the
body’s electrolyte and fluid balance. Excreted electrolytes
include sodium, potassium, chloride, magnesium,
phosphate, and calcium. Normal urine
may contain small amounts of ALBUMIN (protein).
Urine of normal concentration is pale yellow
and has no odor. Dilute urine is colorless; concentrated
urine can appear dark yellow to orange.
Dietary substances, certain medications, and certain
health conditions can alter the color as well as
the odor of the urine. Normal urine is slightly
acidic and has a specific gravity of 1.010 to 1.025,
slightly above that of water. Deviations from normal
urine composition and concentration suggest
various health conditions and may require diagnostic
evaluation.
For further discussion of the urine within the
context of the urinary system’s structure and
function please see the overview section “The Urinary
System.”
See also ALBUMINURIA; ANURIA; CYSTINURIA; HEMA-
TURIA; OLIGURIA; UREMIA; UROLITHIASIS.
urolithiasis The formation of calcifications (also
called calculi) in the BLADDER. Most bladder stones,
like kidney stones, form of calcium in combination
with oxalate (the most common combination),
phosphate, or magnesium. Bladder stones
are less common today than kidney stones
(NEPHROLITHIASIS), though throughout recorded history
bladder stones have been a common urologic
condition. Bladder stones are most likely to form
when URINE remains in the bladder for an
extended time, particularly with URINARY RETENTION
(in which the bladder fails to completely empty
with URINATION). URETHRAL
STRICTURE, CYSTOCELE,
BENIGN PROSTATIC HYPERPLASIA (BPH), long-term BLAD-
DER CATHETERIZATION, and NEUROGENIC BLADDER are
among the conditions that contribute to the formation
of bladder stones. Chronic DEHYDRATION,
such as occurs with drinking too little water, further
contributes to calcification. Bladder stones are
also common during PREGNANCY.
In urinary stasis the minerals dissolved in the
urine begin to settle out when the urine is static
(not moving), forming crystals. The formed crystals
attract more of their composite minerals,
eventually hardening into calculi. Small stones
often easily pass through the urethra in the urine
without the person’s awareness of them. Stones
that are large enough to scrape the walls of the
urethra, or sandlike clumps of calculi that surge
through the URETHRA, may cause irritation such as
DYSURIA (burning sensation) with urination. Other
symptoms may include URINARY FREQUENCY, URINARY
URGENCY, and urinary hesitation (difficulty starting
urination, or start-and-stop urination).
A stone that completely blocks the urethra,
often at the neck of the bladder, causes excruciating
PAIN that may feel as though it arises in the groin or,
in men, in the TESTES (testicles). Often a change in
position relieves the pain, causing the urine to
wash the stone from its point of occlusion. A stone
that is larger than the diameter of the urethra will
intermittently though persistently obstruct the passage
of urine. It may also cause bleeding, resulting
in HEMATURIA (blood in the urine).
The diagnostic path typically includes urinalysis,
ULTRASOUND to detect the presence of stones in the
bladder, and CYSTOSCOPY. Cystoscopy often is both
diagnostic and therapeutic, allowing the urologist
to confirm the presence of stones as well as remove
them from the bladder. Larger stones may require
treatments such as EXTRACORPOREAL SHOCKWAVE