Cloacal Respiration

Fine, Butt Breathing

Ever wonder what happens to turtles during the winter time? Staying above ground would mean freezing to death. The only place that is warm enough is at the bottom of ponds and lakes. While this fixes the freezing-to-death problem, it creates another one: the drowning problem. Turtles breathe air into their lungs to obtain oxygen, but underwater, this is impossible. Luckily, evolution is wiser and more wily than we can imagine. Enter: cloacal respiration.

Turtles sunning in the spring in Central Park

What’s a cloaca?

Cloacas are universal openings that allow for the release of solid waste (poop), urine, and reproductive fluids (semen). A turtle’s cloaca function also includes something called cloacal respiration. Attached to the cloacal opening are two large sacs, called the cloacal bursae. Bumps called papillae line the bursae increasing surface area. Surrounded by dense capillaries, these cloacal bursae allow for diffusion of oxygen into the turtle’s bloodstream and diffusion of carbon dioxide out of the body. This exchange of oxygen and carbon dioxide is exactly the type of gas exchange that happens in the alveoli of the lungs. Different location, same action.

Oxygen Requirement

Without ever having to surface, turtles are able to use the small amount of oxygen they obtain from cloacal respiration to survive. Given their slow metabolism due to the cold temperatures, turtle cells are not creating much ATP and therefore, the oxygen requirement to stay alive is relatively low. The evolution of cloacal respiration reminds me of something Isaac Newton said in his book, The Mathematical Principles of Natural Philosophy:

“Nature does nothing in vain when less will serve; for Nature is pleased with simplicity and affects not the pomp of superfluous causes.”

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