An Excerpt From
CHAPTER TWO: HOW SWALLOWING WORKS
The process of swallowing is more than a one-step “Gulp-and-Gone!” It can be considered to have four phases. You can remember its four parts with the word “POPE” –
1. Preparatory Phase
This phase prepares food for safe swallowing. When you take a bite of food, a remarkable dance begins. Your jaws, teeth, cheeks, and tongue work together to make the food into more or less of a ball.
This “food ball” is called a bolus after the Latin word for ball.
Your lips close tightly so food doesn’t escape from your mouth. Your teeth (or dentures) grind the food into smaller bits. Saliva pours flows from under and around your tongue, moistening food, gathering with it flaky food bits and sugar particles in the neighborhood.
Your tongue mixes and churns the food. It directs the bolus to the side, where your teeth grind it into a dough-like paste.
Your jaws move not simply up-and-down but in a rotary manner that allows for efficient grinding.
Chewing Enhances Flavor
Beyond its mechanical function in reducing a mass of solid food to a pudding-like bolus, chewing adds to the joy of eating. It allows juices and other flavorful food elements to contact your taste buds. It begins the actual digestive process, too, as enzymes start to work while food is in your mouth.
The sense of smell gets into the act as well. Vapors pass through the back of the throat to reach smell receptors in the nasal cavity. That enhances taste and makes ready for further food processing by inviting further saliva flow.
“Tongue, Tongue — Where Are You?”
Just as a skilled dancing duo does not step on a partner’s toes, we (usually) do not chew on our tongue.
Why not? The tongue continuously sends signals to the brain as to where it is and what it is doing. Your gums, cheeks, and palate also send information to the brain so you can work around the tongue without giving it much, if any, thought as you chew.
Breathing and Swallowing
Breathing and swallowing must work together for you to swallow safely. When they don’t, there can be big trouble.
In healthy persons breathing can continue normally during this phase. In those with medical and neurologic disorders, however, it can be challenging if not risky.
And, if – at any age – you are talking, laughing, drinking, and trying to swallow, you are putting yourself at risk. (See Chapters 4 and 5 on Choking and Aspiration.)
2. Oral Phase – Transporting the Bolus
Your tongue is now loaded with food – like a bucket without a handle. During the Oral Phase, the bolus is transported to the back of the throat where the swallowing reflex is triggered.
The exquisite coordination seen in the Preparatory Phase continues:
- Your lips remain closed to prevent food and liquids from escaping from the front of your mouth.
- Your cheeks stiffen and press against your gums and teeth. They provide a lateral barrier to keep food from falling into pockets between cheek and gum.
- Pressed against the bony roof of your mouth, your tongue forms a muscular chute that directs food to the back of the throat.
3. Pharyngeal Phase – The Swallowing Reflex
The highlight of this phase is the swallowing reflex. You could call it the climax of swallowing.
Once the bolus gets to where the tonsils are (or used to be), the swallowing reflex is triggered. The thinking brain is not involved. Swallowing occurs automatically.
Swallowing involves a reflex that invites food in. Gagging and vomiting are reflexive behaviors that throw it out.
Your Swallowing Safety Net
To ensure that food and liquid travel down the correct path – to your stomach, not your lungs — your body has set up a safety net that operates without your conscious direction.
Six hundred or so safe swallows a day. Food and liquid. We swallow saliva even when we’re not eating or drinking. Otherwise, we’d drool.
That’s a big job. The safety net interweaves eight things that happen pretty much at once.
- Breathing stops momentarily.
- The soft palate, which forms part of the roof of the throat, closes off so food doesn’t escape through the nose.
- Muscles of the throat (pharynx) and tongue contract in an orderly manner, moving the bolus to and through the upper part of the esophagus en route to the stomach.
- The hinge-like epiglottis closes over the entrance to the larynx (“voice box”). This keeps food and liquid from entering the respiratory tract.
- The larynx moves forward and upward, likewise preventing food from getting to the lungs while opening the “gate” to the esophagus.
- The vocal cords within the larynx come together, providing yet another mechanism to prevent food and liquid from entering the windpipe (trachea).
- The tongue seals off the throat from the nasal passages and completes it role in pushing the bolus down.
- A ring-shaped muscle, the upper esophageal sphincter (UES), which is normally contracted, relaxes to permit passage of food from the throat to the uppermost esophagus.
After swallowing, breathing resumes.
The entire Pharyngeal Phase normally takes less than a second.
4. Esophageal Phase – Getting to the Stomach
The Esophageal Phase takes the bolus from the UES to the lower esophageal sphincter (LES). Like its upper neighbor, the LES is contracted at rest. It must relax to let food pass into the stomach.
Once the entire bolus gets past the UES, it closes more tightly than ever to guard against backflow (reflux).
The bolus works its way past a temporarily relaxed LES to the stomach by riding waves of rhythmic contractions (peristalsis). It takes from eight to twenty seconds for food to travel the entire esophagus.
Since we usually eat sitting up, gravity – combined with a good supply of saliva — helps the bolus travel through the esophagus.
A Swallowing Walk-Through
Now that we’ve looked at the basics of swallowing on paper, let’s convert this “book-learning” into more practical knowledge and food for thought. Let’s go for a swallowing walk-through.
Tear off a piece of crusty, freshly-baked bread. Hold it in front of you and look at it. Your saliva flows as you anticipate the food about to enter your mouth.
As the food passes your lips, your tongue greets it. Your lips envelop the bread and your tongue mixes it with saliva. It moves the food to the side where your teeth can begin their work.
Your jaws move up and down, side to side. This rotary action grinds the bolus further. It is becoming pasty. Your tongue gathers the bolus into a central hollow in the middle of your throat and holds it against the hard palate.
You can continue to breathe while you chew. Like a track athlete getting ready for a big jump, you gather energy and breath. Your tongue presses the food against the hard palate. Your lips continue their tight seal as your cheeks stiffen further, closely applied to your teeth and gums.
The Moment of Truth
Now that the food has been brought to the back of the throat comes the moment of truth: the swallow itself. You hold your breath. Your Adam’s apple rises as your throat muscles contract. You swallow. Your food begins the downward part of its journey. You resume breathing.
Your tongue searches out remnants of food that may be hiding between gum and cheek. You swallow one or several times more to finish things off. The final swallow is little more than saliva.
Congratulations! You’ve swallowed safely.