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The organs, tubes,
muscles, and nerves that
work together to create,
store, and carry urine are
the urinary system. The
urinary system includes
two kidneys, two ureters,
the bladder, two sphincter
muscles, and the urethra.
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Excretion is the process of removing wastes
and excess products from the body
Three of your body systems are involved in
excretion:
– Your skin releases waste products and water
when you sweat
– Your lungs expel carbon dioxide and water
when you exhale
– Your urinary system removes waste products
from your blood
Cleaning the blood
Your blood is like a supply train that comes into a
town to drop off supplies and take away garbage
The train has to find a way to get rid of the garbage
before it can load up with more supplies.
If the garbage is not removed,
the townspeople will be in
a very unhealthy environment
Kidneys
The kidneys are a pair of beanshaped organs that
constantly clean the blood.
Your kidneys filter about 2,000
liters of blood each day
Your body only holds 5.6 liters
of blood, so your blood
cycles through the kidneys
about 350 times a day
Inside each kidney are
more than 1 million
microscopic filters
called nephrons
Nephrons remove a
variety of harmful
substances from the
body.
How the Kidneys Filter Blood
A large artery brings blood
into each kidney
Tiny blood vessels branch
off the main artery and
pass through part of
each nephron
Water and other
substances are forced
out of the blood vessels
and into the nephrons
As these substances flow
through the nephrons, most
of the water and some
nutrients are moved back into
blood vessels
A concentrated mixture of waste
materials is left behind in the
nephrons
The cleased blood leaves each
kidney in a large vein to
recirculate in the body
Urination
The yellow fluid that remains in
the nephrons is called urine
Urine leaves each kidney
through a slender tube called
the ureter and flows into the
urinary bladder
Urine leaves the body through
another tube called the
urethra
Urination is the process of
expelling urine from the body.
Water In, Water Out
Our bodies would swell up
with excess water if we did
not excrete as much water
as we take in.
 The balance of fluids is
controlled by chemical
messengers in the body
called hormones

Sweat and Thirst
When you get hot, you lose
more water in the form of
sweat
The evaporation of water from
your skin cools you down
As the water content of the
blood drops, the salivary
glands produce less saliva
This is one of the reasons you
feel thirsty.
Antidiuretic Hormone
When you get thirsty, other parts of your body react to the
water shortage
A hormone called antidiuretic hormone, or ADH, is released
ADH signals the kidneys to take back water from the
nephrons and return it to the bloodstream, thereby
making less urine
When your blood is too watery, smaller amounts of ADH
are released
The kidneys react by allowing more water to stay in the
nephron and leave the body as urine
Diuretics
When you are thirsty, your tissues
are asking for more water
Some beverages contain caffeine,
which is a diuretic
Diuretics cause the kidneys to
make more urine, which
decreases the amount of
water in the blood
So instead of giving your body
more water, caffeinated
beverages cause additional
water to be lost in urine
Urinary System Ailments
Since the urinary system regulates body
fluids and removes wastes from the
blood, any malfunction can become lifethreatening
 Some common urinary system disorders
are:
– Bacterial infections
– Kidney stones
– Kidney disease
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Bacterial Infections
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Bacteria can get into the bladder and
ureters through the urethra and cause
painful infections
It is important to treat such an infection
early because it could spread to the
kidneys and lead to permanent damage
Drinking six-eight 8 oz glasses of water
can help prevent these infections
Kidney Stones
Sometimes salts and wastes
collect inside the kidneys
and form kidney stones.
Kidney stones interfere with
urine flow and cause pain
Most kidney stones pass
naturally from the body,
but sometimes a medical
procedure is necessary
Kidney Disease
Damage to nephrons can prevent
normal kidney functioning, leading to
kidney disease
If the kidneys do not function properly, a
kidney machine can be used to filter
waste from the blood.
The machine pumps blood from an
artery in the forearm or wrist to a
kidney machine, where it is filtered.
 The cleaned blood is then pumped
back into a vein in the arm.