Page "Giraffe" Paragraph 39

The circulatory system of the giraffe has several adaptations for its great height.

Its heart, which can weigh more than and measures about long, must generate approximately double the blood pressure required for a human to maintain blood flow to the brain.

Giraffes have unusually high heart rates for their size, at 150 beats per minute.

In the upper neck, the rete mirabile prevents excess blood flow to the brain when the giraffe lowers its head.

The jugular veins also contain several ( most commonly seven ) valves to prevent blood flowing back into the head from the inferior vena cava and right atrium while the head is lowered.

Conversely, the blood vessels in the lower legs are under great pressure ( because of the weight of fluid pressing down on them ).

To solve this problem, the skin of the lower legs are thick and tight ; preventing too much blood from pouring into them.