|MadSci Network: Development|
Can an infant breath and swallow simultaneously? The pharynx (the combination of your air and food tube) was surrounded by branchial arches during embryological development. The substance of the arches form most of the bony structures of the face and throat. These arches are often called "gill arches" in the developing embryo, because that is what they look like. But they are not gills -- at least not gills in the same sense as when we say that a fish has gills. They may be holdovers from our Devonian ancestry (about 450 million years ago), but then it would be more correct to say that fish gills and land animal faces both develop from the branchial arches. One of the innovations associated with the evolution of mammals was the development of mammary glands (the defining characteristic of a mammal) and the nursing young. Some young mammals will attach their mouths to the nipple almost continuously. In this case, they need to drink milk and breath at the same time. The innovation that allows this is the palate and the high location of the larynx (the voice box and the beginning of the air tube). A nursing mammal can suck milk into its mouth, and thanks to the palate its mouth is separate from its nasal cavity. So while it is sucking in milk, it can also breath through its nose. When the mammal is ready to swallow, the soft palate (the back of throat with the dangling uvula attached to it) rapidly moves upward to close off the back of the nasal air tube. At the same time, the epiglottis closes off the larynx and guides the milk into the esophagus (the food tube). Because of these innovations, the young mammal can breath and swallow in quick succession. It is not simultaneous, but it is pretty close. Humans add an extra wrinkle to this problem. Although we are born with a fairly typical mammalian pharynx, the larynx moves down to a lower position in our throat as we grow older. This leaves a large gap between the back of the mouth and the top of the larynx. For adult humans, the act of swallowing becomes a very delicate process. The fact that we frequently choke on "food going down the wrong tube" shows how easily this process can be disrupted.
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