Natures wonders: giraffe circulatory system (Introduction)

by David Turell @, Thursday, October 20, 2016, 14:26 (1151 days ago) @ David Turell

An excellent description:

http://nautil.us/issue/41/selection/how-necking-shaped-the-giraffe-rp

Let’s start with the most obvious. The giraffe’s great height poses a number of difficulties that have been overcome via some notable adaptations. In order to pump blood seven feet above the animal’s heart to that towering head, an exceptionally high blood pressure is required, as much as three times the human systolic level. In order to keep from blowing their arteries apart, giraffes need special structural supports within those blood vessels.

In the other direction, to prevent blood from pooling in their feet, which are at the end of some very long legs, giraffes have evolved the equivalent of compression stockings, like those that people use post-surgery or to prevent deep vein thrombosis on long airplane rides. The giraffe’s hack consists of highly elastic blood vessel walls, combined with an extensive capillary bed. By restricting perfusion of fluid into surrounding tissues, these structures keep a giraffe’s blood in its vessels, where it belongs, rather than in surrounding tissue. These animals have another specially adapted compression system in their necks, which prevents too much blood from rushing to their heads when they bend down to drink—which they don’t do very often, since they get most of their water from the leaves they eat, using their highly flexible 18-inch tongue.

As notably long as are giraffe necks, these are actually outclassed by their legs, such that those monumental necks are—believe it or not—too short to comfortably reach a puddle; as a result, a drinking giraffe must splay its front feet wide apart. And, by the way, the same fluid sluice-way control mechanism in its lengthy neck works in reverse when a giraffe is done drinking and eventually raises its high head, allowing only a relative trickle of blood to flow back down so that its brain doesn’t suddenly become hypoxic.

Comment: The article contains lots more about the recurrent laryngeal nerve, the animals strange movement pattern and its sex life. Worth a read. One can only wonder why evolve such problem animal which requires all of these adaptations. How many mutations are required? Chance or saltation?


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