A giraffe’s “extraordinary net”

Giraffe will generally drink about 12 litres of water a day but a large bull can consume up to 48 litres. With their long necks one might wonder how they manage when lowering their heads to drink. The heart of a giraffe is not strong enough to pump blood two-and-a-half metres to the head when upright so there is a special muscular artery in the neck that works as an extra pumping organ to support the heart in increasing the flow and blood pressure in the neck. But once they lower their heads there is the problem that their brains aren’t built to handle the extra pressure. That is why there is a complex network of fine veins at the base of the brain called the “extraordinary net” which lowers the blood pressure and regulates the flow of blood to the brain. These vessels expand once the neck starts to be lowered to accommodate the excess blood flowing in under pressure, and then contract when the head is raised again.