On Whale Throats and Nostrils

A couple of weeks ago, a Today I Found Out article about the unique anatomy of whale throats made its rounds on Digg. The article centers around the interesting fact that whales’ respiratory tracts (nasal passage, trachea, lungs) and digestive tracts (mouth, esophagus, stomach, etc.) are much more isolated from each other than those of terrestrial mammals—the upshot being that it’s impossible for something (for example, Dory and Marlin in the movie “Finding Nemo”) to enter a whale through the mouth and come out of the blowhole.

Well, that’s not quite right. While the article correctly points out that toothed whales typically only have one blowhole and baleen whales typically have two, it glosses over another very important distinction: baleen whales’ respiratory and digestive tracts actually are connected. (Dolphins and toothed whales, on the other hand, do have completely independent digestive and respiratory tracts, as the article states.)

So, after being swallowed by a humpback whale in the movie, Dory and Marlin could in fact have escaped through the whale’s blowhole instead of being digested.

That said, this whole business of how a whale’s throat is set up can get pretty weird. For starters, consider that mammalian body plans require that our digestive and respiratory tracts cross each other. Because our mouth is ventral to (closer to our bellies than) our nose, while our trachea (windpipe) and lungs are ventral to our esophagus and stomach, our digestive and respiratory tracts have to form a T intersection in our throat.

A flap of muscle called the epiglottis keeps food and water from entering our lungs when we swallow, but otherwise stays open so air can get to our lungs.

In that regard, baleen whales basically have the same anatomy as us. The only difference is that their epiglottis is a lot more robust. Instead of a simple flap, it’s a tube that extends from their windpipe into their nasal passage. When they swallow, the tube collapses, opening the passage between the mouth and the esophagus, while closing the passage between the nose and the windpipe. If Dory and Marlin wanted to get from the humpback whale’s mouth to its blowhole, this is how they’d do it.

The windpipes and esophagi of toothed whales, on the other hand never meet. But they also don’t simply go around each other, as you’d imagine. Instead, the esophagus forks to either side of the trachea on its way to the stomach. So instead of a highway overpass, it’s a little more like a subway line emerges in the median of a highway, then crosses over one set of lanes.

Another interesting factoid from the TIFO article: while toothed whales only have one blowhole (which is their equivalent of a nostril), they do have two nasal passages—it just happens that one of them is sealed up. Guess what these whales use that closed nasal passage for? Echolocation!

So does this mean that baleen whales, which use both of their nasal passages for breathing, don’t echolocate? So far, the answer seems to be yes. While baleen whales have been recorded emitting clicks and other noises similar to the ones used by whales and dolphins to echolocate, it’s not clear that that’s what those noises are for. The bottom line is that we know too little about our massive aquatic cousins to know for sure.