URINATION, PAINFUL
THE URINARY TRACT
Also known as the urinary system, the
urinary tract consists of the kidneys, in
which urine is formed to carry away
waste materials from the blood; the
ureters, which transport the urine from
the kidneys; the bladder, where the
urine is stored until it can be
conveniently disposed of; and the
urethra, through which the bladder is
emptied to the outside. The kidneys
require a large blood supply and are
connected close to the body’s main
artery, the aorta. More than a litre of
blood passes through the kidneys
every minute.
The filtering units
Each kidney has about one million of these
units, which form dilute urine by filtering
the blood.
COMPOSITION OF URINE
Urine consists almost entirely of
water, with only small amounts
of urea (the main waste product),
other waste products (e.g.
creatinine and uric acid), and
sodium chloride (salt).
96% water
2% urea
1% sodium
chloride
(salt)
1% other
waste
products
Interior of bladder
The two ureteral openings, shown on the right,
and the urethral orifice form a triangle at the
base ofthe bladder. In males, the urethra runs
through the bodyofthe prostate gland situated
below the bladder.
Pelvis
Calyces
Medulla
Cortex
Renal c a p su le
_____
Collecting system
From the tubules that lead
from the filtering units, much
ofthe water and some other
substances are reabsorbed
into the blood. The remaining
more concentrated, urine
runs into collecting ducts and
then into the pyramid-shaped
calyces ofthe kidney and
kidney pelvis. From there, the
urine passes into the ureter.
X-ray showing urinary tract
The X-ray on the left, taken using
the technique of intravenous
urography, shows (as lighter areas)
the calyces and pelvis of each
kidney, the ureters and bladder,
as well as the bones ofthe lower
spine and pelvic girdle.
Kidneys
The two kidneys lie
within large pads
of fat on the inside
ofthe back wall of
the abdomen, close
to, and on either
side of, the spine.
Each kidney consists
of an outer cortex,
an inner medulla, and
a urine-collecting
system that includes
the calyces and the
pelvis ofthe kidney.
Bladder
The muscular bladder
wall can stretch to
accommodate about
half a litre of urine,
but atthisvolume,
the desire to pass
urine is very strong.
Prostate
(male only)
Ureter
U
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