Just like we don’t have to think about breathing, when we swallow almost all of the time it is automatic. However, swallowing is pretty complex and requires quite a few nerves, muscle and gut interaction to work right.
If you think about it, food, water and sputum need to be transported from the mouth to the stomach via the esophagus. The esophagus is a long tube, if you will, which connects to mouth to the stomach and points beyond.
Yet along the way lurks very real danger. The airway shares the mouth with food water and sputum. If any and or all of these substances make it into the airway then bad things such as aspiration pneumonia or inflammation can happen.
So what nature has done is to create a pretty ingenious system to prevent aspiration or the passage of anything but air into the airway. When we swallow the airway is automatically closed off, so the only opening available is via the esophagus.
Unfortunately, like any device breakdowns can and do occur. If the nerves are working say because of a stroke, then the coordination of the swallowing motions can be lost. If there is a tumor preventing the valve to the airway from closing, then food and such can end up in the wrong pipe. If the alertness is decreased such as with alcohol or drugs or during general anesthesia, then the coordination is also lost. If we choke on something, that means that food or water might have entered the airway.
The result is recurring bouts of pneumonia. To prevent the pneumonia, the system needs to be fixed, or if impossible, say with a major stroke, then alternative methods for introducing food and water have to be used. These include gastric or jejunal feeding tubes which are placed directly into the gut, thus avoiding the mouth and TPN in which nutrition and hydration are accomplished solely through the veins. Each has major side effects.