Why Snakes Don't Faint!

Paul Donovan considers the remarkable ways in which snakes can function, thanks to their circulatory systems, which are highly tuned to reflect their individual lifestyles.

- Paul Donovan

When I was writing an article on giraffes for another magazine, it raised the question - when a giraffe bends down, why does blood not rush to its brain? My mind then switched to snakes. When a snake climbs a tree, what prevents blood rushing to its tail? Equally, when one of these reptiles then descends back to the ground, why does blood not immediately rush to its head?

High and low blood pressure

The answer, of course, is that a system must be in place to prevent this from happening, because otherwise it would be extremely dangerous for the animal. And of course, there is! When lying flat on the ground, a terrestrial snake’s circulatory system works with relative ease, as gravitational pressure is not placing any undue stress on it.

But it becomes a different situation, however, once a snake climbs up or down a tree. This is when gravity comes into play, by increasing the demands on the cardiovascular system as, all of a sudden, the body has changed position significantly. When a snake begins to climb, the blood pressure in the centre of the body rises, that in the head area decreases, and blood begins to pool in the tail.

As the snake climbs up a tree, its blood vessels could suddenly deform, causing the walls to become distended as a result of gravitational pressure being placed on the system. This would then lead to plasma escaping from the capillaries. As blood pressure drops, vital organs would not receive sufficient blood, and would be at risk of failing, threatening the snake’s survival. These reptiles therefore have a circulatory system which is adapted to work against the forces of gravity.

The importance of posture