Why do I choke and cough when something goes down the “wrong tube”?
For the body to survive it has to bring in enough oxygen and get rid of enough carbon dioxide. You breathe in air through your nose and mouth and it moves back into your throat (pharynx) before passing down through your trachea into your lungs. Everything else (food and drink) your body needs to survive must come in through your mouth, move back into your pharynx and then enter your gastrointestinal system by passing down your esophagus. Since the air we breathe and the food and drink we bring in share the pharynx in common, the dilemma the body faces is like what the engineer of a train faces when approaching a fork in the track. Air can enter the gastrointestinal system without causing harm. But if enough food and drink enter the lungs, this can greatly limit (or totally prevent) them from bringing in enough oxygen and getting rid of enough carbon dioxide, resulting in death by asphyxiation. So, just as the engineer has to know whether or not to throw a switch for the train to go down the “right track” so too, the body has to know what to do so its food and drink won’t go down the “wrong tube”. It does this through the swallow and cough reflex.
A reflex is an involuntary pre-programmed, automatic motor response to a stimulus which comes about without conscious direction from the brain (e.g. blinking). It works through the spinal cord and/or the brainstem and serves to protect the body from injury. As the contents of the mouth mixes with saliva, it is worked on by the teeth and the tongue, formed into a small mushy lump called a bolus, and moved back toward the pharynx. Up until this point everything the body has done (bringing in food and drink, chewing, and moving it into the pharynx) has been voluntary. But once the bolus reaches the pharynx, the body must automatically take control to be sure that it goes into the esophagus and not into the lungs. Sensors in the pharynx detect the bolus and send information to the brainstem where it is integrated. The brainstem then initiates the swallow reflex by sending out nerve messages. These signals result in the coordinated contraction of over twenty different muscles that moves the food and drink downward while at the same time lifting the pathway to the trachea and lungs up and out of the way.
While looking in a mirror, if you gently place your fingers on the front of your neck (just below the jaw) and swallow a few times, you will see and feel the tissue in the neck move up and down. What you are feeling and seeing is the upper parts of your respiratory system being moved up and out of the way so the airway can be protected from what is being sent down into your esophagus. Think about it. This marvel of engineering takes place within about a second and flawlessly repeats itself about a thousand times a day. If even the slightest amount of material is allowed to go down toward the trachea, sensors in this region bring on the cough reflex which usually is able to propel it back up, either into the proper path and back down into the esophagus, or expel it back out of the mouth. So, that’s why you choke and cough when something goes down the wrong tube.
Three Questions for Mr. Darwin
- Besides wondering which of the more than twenty muscles came first (since they’re all needed for swallowing to work properly), where did the information come from that tells my brainstem how to coordinate their action for swallowing?
- Since the distance from my pharynx to the path leading to my lungs is very short and (due to muscular contraction and gravity) food and drink move quickly, how did my brainstem learn how to act fast enough to protect my airway?
- Where did the information come from that taught my brainstem when, how fast and how hard, to apply my cough reflex to prevent me from dying by asphyxiation?
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Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.
Copyright 2017 Dr. Howard Glicksman. All rights reserved. International copyright secured.
