When you swallow, your throat (also known as the pharynx) undergoes a complex series of muscle contractions and relaxations to move food and liquid from your mouth down to your esophagus and stomach. Swallowing, known medically as deglutition, is an intricate process that allows us to eat and drink safely.
The Phases of Swallowing
There are three main phases to the swallowing process:
- The oral preparatory phase
- The oral phase
- The pharyngeal phase
The Oral Preparatory Phase
The oral preparatory phase is when you chew and manipulate the food in your mouth to form a bolus (a soft mass of chewed food). Your lips, cheeks, tongue, teeth, and saliva all work together to moisten the food and shape it into a cohesive mass that can be swallowed.
The Oral Phase
Once the bolus is formed, the oral phase begins. Your tongue rises to press the bolus against the hard palate, pushing it to the back of your mouth. At the same time, your soft palate lifts to close off your nasal passageways. This prevents the food from entering your nasal cavity.
The Pharyngeal Phase
As the bolus reaches the back of your mouth, it enters the pharynx (throat). At this point, the pharyngeal phase begins. There are several important steps in this phase:
- Your larynx (voice box) and hyoid bone lift up and forward under your chin. This opens the airway to allow the bolus to pass through.
- The epiglottis tilts backwards to cover your larynx, preventing food from entering your windpipe and lungs.
- Muscles in the back of your throat contract, propelling the bolus downwards.
- Your upper esophageal sphincter (a ring of muscle at the top of the esophagus) relaxes, allowing the bolus to enter your esophagus.
Once the bolus enters the esophagus, muscles in the esophageal wall contract in a wave-like motion called peristalsis. This pushes the food down to your stomach for digestion.
Anatomy of the Throat
To understand how swallowing works, it helps to know the anatomy and muscles involved:
Oral Cavity
The oral cavity includes your lips, cheeks, teeth, gums, tongue, hard palate (roof of your mouth), and soft palate. Food is chewed and prepared for swallowing in the oral cavity.
Pharynx
The pharynx is a funnel-shaped tube about 5 inches long that serves as a passageway for both food and air. The pharynx has three parts:
- Nasopharynx – upper part behind the nasal cavity
- Oropharynx – middle part behind the oral cavity
- Laryngopharynx – lower part behind the larynx
Epiglottis
The epiglottis is a flap of elastic cartilage attached to the entrance of the larynx (voice box). During swallowing, it tilts backwards to prevent food and liquid from entering the trachea (windpipe).
Hyoid Bone
The hyoid bone is a U-shaped bone located above the larynx that helps support the tongue muscles. It lifts up during swallowing to aid in opening the esophagus.
Larynx
The larynx, also known as the voice box, houses the vocal folds and connects the pharynx to the trachea. It lifts up and forward during swallowing.
Esophagus
The esophagus is a muscular tube connecting the pharynx to the stomach. Food passes from the pharynx into the upper esophageal sphincter before traveling down the esophagus via peristalsis.
Muscles Involved in Swallowing
Dozens of muscles in the mouth, tongue, pharynx, larynx and esophagus work together to accomplish swallowing:
| Muscle Group | Major Muscles | Role in Swallowing |
|---|---|---|
| Mouth and Tongue | Orbicularis oris, buccinator, risorius, genioglossus, styloglossus | Manipulate food, form bolus, position bolus between tongue and palate |
| Soft Palate | Levator veli palatini, tensor veli palatini, palatoglossus | Elevate soft palate to close off nasal passages |
| Pharynx | Superior, middle and inferior pharyngeal constrictors | Squeeze pharynx to propel bolus downward |
| Larynx | Thyrohyoid, digastric, stylohyoid, mylohyoid, geniohyoid | Lift larynx upward and forward |
| Esophagus | Cricopharyngeus, esophageal sphincters | Relax to allow bolus into esophagus. Peristalsis pushes bolus to stomach. |
Swallowing Disorders (Dysphagia)
Sometimes disorders can affect the complex swallowing process. Dysphagia is the medical term for swallowing difficulties. Some common causes of dysphagia include:
- Muscle weakness or incoordination from neurological conditions like stroke or Parkinson’s disease
- Medical conditions like acid reflux or diabetes that can damage the esophagus
- Head and neck cancers, which can restrict food passageways
- Gastroesophageal reflux disease (GERD) can cause scar tissue that narrows the esophagus
- Physical obstructions like benign tumors or foreign objects lodged in the esophagus
Symptoms of dysphagia can include:
- Difficulty controlling food/liquid in the mouth
- Difficulty initiating a swallow
- Coughing or choking during meals
- Nasal regurgitation when swallowing liquids
- Food sticking in the throat or chest
- Heartburn or reflux
Dysphagia can increase the risk of pneumonia, malnutrition and dehydration. Seeking treatment is important, as severe dysphagia can become life threatening. Speech pathologists can provide swallowing therapy, while doctors may recommend surgery or endoscopic procedures to address any obstructions.
Swallowing and the Brain
Swallowing is controlled by a complex neurological sequence. It involves cranial nerves, sensory receptors, motor functions, and central coordination by the brainstem and cortex:
- Sensory receptors detect the presence and properties of food in the mouth.
- Cranial nerves like V, VII, IX, X and XII carry signals to initiate swallowing sequences and muscular contractions.
- The tongue and jaw perform motor functions to chew and position the bolus.
- The brainstem controls involuntary aspects like gag reflexes and pharyngeal contractions.
- The cerebral cortex regulates voluntary components like timing of swallowing.
Damage to the neurological system through stroke, neurodegenerative disease, or traumatic injury can impair the ability to swallow safely. Understanding the neurological basis of dysphagia is key for proper diagnosis and management.
Interesting Facts About Swallowing
- The average person swallows around 2,000 times per day.
- It takes under 1 second for a food bolus to pass through the pharynx.
- The cricopharyngeus muscle at the top of the esophagus stays contracted except during swallowing to prevent air from entering the esophagus.
- Newborns have a reflex called the glottic closure reflex that closes their vocal cords when swallowing to prevent inhaling food. This reflex disappears around 6 months.
- An adult’s esophagus is about 10 inches long. A newborn’s is just 2 inches long.
Conclusion
Swallowing is a remarkably fast and intricate process. It involves almost all the structures of the mouth, pharynx, larynx and esophagus working together in precise coordination. Dysphagia, or disordered swallowing, can have serious health impacts. Understanding the anatomy and physiology behind normal swallowing is essential for managing swallowing disorders. While swallowing happens effortlessly around 2000 times a day, it relies on a complex neuromuscular system to work properly.
