Giraffes are the tallest terrestrial vertebrates (males stand about 20 feet tall, females slightly less), which opens up leafy resources other browsers like the stately kudus lack, but also present a host of problems for survival.
That long neck that makes up 50% of their height makes it a challenge to pump blood against gravity up to the brain. Consequently, their highly muscular, thick-walled heart has to generate more than twice as much pressure as the human heart does. (Giraffe blood pressure runs about 280/180–normal human blood pressure is about 120/80 or lower). That’s fine for getting blood to the brain, but blood flow is all downhill to the feet, so how do giraffes keep from getting swollen ankles? With tight-fitting, elastic skin that acts like compression stockings, the kind they give heart patients to wear.
Their height also gives them a bird’s eye view of their surroundings, including predators perhaps lying in wait in the grasses below, but that same height advantage becomes a disadvantage when giraffes need to awkwardly bend over for a drink or food on the ground.
Just getting into position for a drink or a bite of something on the ground is a mechanical problem in itself. But lowering its head below the level of the heart poses a great risk of cerebral hemorrhage. To combat this potential physiological disaster, arterial pressure sensors detect changes in head position and cause an immediate decrease in heart rate and heart contraction strength to decrease blood pressure.
Great vertical height poses problems for other organ systems as well.
Very long necks require very long nerves running from the brain to the periphery. For example the nerve that stimulates the vocal cords and muscles that enable swallowing is 5-6 feet long! It better conduct very fast, or food will go down the wrong tube (i.e., the trachea) when they swallow.
Giraffes love to browse on acacia leaves, but the plants have a great plenty of protective thorns, which the giraffes’s almost prehensile lips and tongue seem adept at working around.
With their graceful walking stride and elevated height, giraffes just epitomize the “gentle giant” title.