How You’’re Different
From a Pigeon
Meet Manny.
Meet Jan.
Name: Manny
a.k.a.: pigeon, bird, flying rat, nuisance
Diet: seeds, insects, larvae, and sidewalk leftovers
Biggest Fear: traffic
Name: Jan
a.k.a.: human being, girl, Janet, Jan-Jan
Diet: fish sticks, granola, and bananas
Biggest Fear: pigeon paintball
© 2008 Scholastic Canada Ltd. V001
How You’re Different From a Pigeon 1/6
Believe it or not, you have a lot in common with both Manny and
Jan. You eat food and digest it. And after eating and digesting, you
have waste to clean up. There are two main kinds of waste:
• Leftover bits of food and other stuff that your body can’t
digest or needs to get rid of. This is handled by your
digestive system.
• The waste products of all the work your body does. Some
of this is handled by your blood and kidneys, which are an
important part of your excretory system.
Whatever the waste, it has to go, or it can become toxic. If you
don’t excrete your waste, you’ll get sick.
And when it comes to excretion, you and Jan are a lot different
from Manny!
How You’re Different From a Pigeon 2/6
Manny: When grooming
his feathers and grazing
the sidewalk gets boring,
Manny flies high above
the city, using cars,
lampposts, and even
people for paintball
practice. His “paint”?
Excretions from his
body—a.k.a., bird poop!
Stomach and
Other Stuff
Digests food. At the end
of digestion, Manny’s
blood carries nutrients
throughout his body while
leftovers get pushed out.
Kidneys
Here, teeny tiny little filters called nephrons (NEFF-ronz)
remove waste from Manny’s blood. In mammals, the waste
is stored for a while. Manny’s body is designed to fly and he
can’t carry anything extra. So, his kidneys send the waste
right out, in the form of lightweight uric acid. (That’s what
makes bird poop white!)
Gross, you say? Not at
all! Manny’s excretory
system is fascinating!
Ureter
Exit tunnel for waste from kidneys
Cloaca
Mammals have different exits for different
waste products. Just one will do for Manny!
How You’re Different From a Pigeon 3/6
Renal Arteries
Jan has to excrete
waste products, too.
Luckily, she does not
find humour in tricks
like Manny’s. (Poor Jan!
As a city dweller, she
has been a paintball
victim more than
once.) Jan’s urinary
system is one of the
most important ways
that her body rids
itself of waste.
Stomach and
Other Stuff
Food gets digested
here. Jan’s body uses
what it needs, and
the leftovers leave
by their own exit.
Bladder
Gradually fills with urine from
Jan’s kidneys. When it’s about
halfway full, nerves inside send a
message to her brain, telling her,
“Time to go!”
Just like Manny’s, Jan’s blood needs a
little cleanup after circulating nutrients
throughout her body. It flows
into her kidneys through Jan’s
renal arteries.
Kidneys
Jan has two, but she could
survive with just one. Each is
about 13 cm long and 8 cm
wide. They work constantly,
filtering from 4 to 6 L of blood
400 times a day!
Ureters
After Jan’s nephrons have done
their work, clean blood flows on
and waste is combined with water
and becomes urine. Tubes called
ureters carry it to the bladder.
Urethra
The urethra connects the bladder
to the outside of Jan’s body. It’s
2.5 to 5 cm long. If Jan were a boy,
it would be about 20 cm long.
How You’re Different From a Pigeon 4/6
More about Manny, Jan,
and Excretions
No Sweat!
Manny has a great
ventilation system
that’s built right
in—or rather, on! His
feathers help to keep
him warm during the winter and cool
during the summer. So he doesn’t need to
produce another famous excretion—sweat!
Working
Birds
Nowadays
people tend
to think pigeons
are a real pain. But
ne, or
before there was Internet, telepho
y useful
even mail ser vice, pigeons were ver
were
to human beings. Homing pigeons
longused as a way to send messages
up to 145
distance. A homing pigeon can fly
limit on
km/h. That would break the speed
Canadian highways!
Fast Food
Because storing his food—like storing urine—would only weigh
Manny down, he has a unique digestive system. It digests an
entire meal and gets rid of the leftovers in about 3 hours. For a
human being, it’s about 24 hours from start to finish.
How You’re Different From a Pigeon 5/6
Body Balance
The kidneys’ most important job
is homeostasis: balance in the
body. One thing that has to be
balanced is fluids and minerals. On
a sunny summer day when Jan is
out skateboarding, she gets hot.
Her body squirts out sweat through
millions and millions of microscopic
sweat glands. Jan’s sweat is made
up of mostly water with a little bit of
salt, but it also contains urea—the
same chemical found in Jan’s urine!
Reduce, Reuse
,
Recycle
In olden days
, urine wasn’t
flushed away
so quickly. It
wa s
saved in pots
and used in th
e
laundry to rem
ove grease st
ains.
Weavers used
old urine to m
ake
stronger, thick
er woollen clo
th,
and dyers use
d it to set colo
urs
more firmly.
How You’re Different From a Pigeon 6/6