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As the tallest of all land animals,
giraffes easily browse on food
in the tops of trees.
Getting a drink of water may not be so easy.
But giraffes face
an even greater challenge:
overcoming gravity.
Gravity makes fluids flow downhill easily.
But to move it up, you have to overcome
the downward pull of gravity.
The higher a fluid has to go,
the more pressure you need.
In an adult giraffe’s case,
this could mean pumping its blood
two or more meters, six feet or more,
above its heart.
To do this, the giraffe must generate
very high blood pressure
—much higher than that of all other mammals,
about twice the normal pressure
found in humans.
Such elevated pressure in humans
or other mammals causes serious problems,
from swollen legs
to kidney and heart failure or strokes.
How does the giraffe handle
such high pressure
without getting sick or dying?
While we don’t fully understand
all of the details,
scientists have discovered some intriguing
features of giraffes that may help.
Adult giraffes have hearts
with extra-thick muscle.
In humans, high blood pressure
causes thicker heart muscle
that can become very stiff,
reducing its effectiveness.
But the giraffe’s heart stays flexible
and pumps blood very efficiently.
When a giraffe stops to drink
and lowers its head,
you’d expect a surge of pressure in its head.
But the giraffe isn’t harmed
by extreme pressure in this position.
Why not?
There’s more to the story,
but here’s one thing:
Giraffes either spread their forelegs
or bend them when they drink,
reducing the vertical distance
between the heart and head.
Even when it lifts its head
in one quick sweeping movement,
the blood flow is controlled
and keeps the giraffe from fainting
because of insufficient blood flow
to the brain.
Compared with the giraffe’s neck arteries,
the arteries in the lower parts of its legs
have thicker walls
and smaller internal diameters.
And ring-shaped muscles tighten
to restrict the flow of blood into the legs
or relax to allow more blood to flow.
This mechanism
could help contain the higher pressure
in its lower body and avoid swelling,
almost as if it were wearing
compression socks!
A better understanding
of the giraffe’s cardiovascular system
might help doctors explore new approaches
to managing high blood pressure.
Giraffes may even help scientists
build better space suits.
In the near vacuum of space,
space suits must maintain enough pressure
on an astronaut’s body
to keep blood and other fluids liquid
and keep the astronaut alive.
However they do it, one thing is certain:
Giraffes thrive
with a high internal blood pressure
that would harm us.
What do you think?
Did the giraffe’s
high-pressure circulatory system evolve?
Or was it designed?

Was It Designed? The Circulatory System of the Giraffe