Blood Pressure Regulation in Giraffes

Giraffes (Giraffa camelopardalis) are the tallest of all land animals. Their scientific name comes from the Ancient Romans, who described these animals as having a camel's body with a leopard's spots. Their almost comically long necks make giraffes instantly recognizable and allow them to reach vegetation at the tops of trees. This length may cause you to ponder the question of how blood gets all the way up to the giraffe's head?

Height

At birth, giraffes stand 6 feet tall, taller than the average adult human. Male giraffes can grow to be 18 feet tall and weigh 4200 pounds, and females up to 16 feet and 2500 pounds. Their long legs and necks enable them to feed on vegetation at the tops of trees in the African savannah that other animals cannot reach.

Blood Pressure

Because the giraffe's head is so much farther above its heart than in any other creature (8 to 10 feet), it takes a lot of power to get blood up there. To accomplish this, giraffes have huge hearts of around 25 lbs. (40 times larger than human hearts), along with extremely high blood pressure, nearly twice that of humans.

Adaptation

Giraffes' extremely high blood pressure would be extremely dangerous in humans and other animals; however, giraffes have adapted to it by the process of natural selection. This means that animals that could not handle the trait died out, so that only those that survived were able to breed and carry on the trait.

Regulation

When giraffes bend down to take a drink of water (not such an easy task with such long legs--they must splay their legs out to almost a 45-degree angle to reach the ground!), a series of valves in their neck veins slow the blood flow and keep blood from rushing to the head. This adaptation was necessary because without it, the rush of blood to the head due to extremely high blood pressure would cause severe damage every time they bent down.

Measurement

A series of experiments in the 1950s by German scientist R.H. Goetz were the first to provide a measurement of blood pressure in giraffes. Goetz trapped wild giraffes and inserted a custom-made manometer (an instrument that measures blood pressure) inside their inch-thick hides. The resulting blood pressure measurement was 200 mmHg when the giraffe was standing, yet when its head was lowered, there was no rush of blood to the brain--in fact, it decreased to a safe (for them!) level of 175 mmHg.

References

• Giraffe page, Smithsonian National Zoological Park website
• Hypertension and counter-hypertension mechanisms in giraffes. Cardiovasc Hematol Disord Drug Targets. 2006;6(1):63-67.
• "Science: The Giraffe Problem" from Time Magazine