Overview - The Pharynx
Doctors prefer to use the more precise term "pharynx". Pharynx describes the part of the throat that begins from behind the nose to the beginning of the voice box and the oesophagus.
The nasal airway and the food passage share the same pharyngeal passage to conduct air and food. After passing the pharynx, the airway goes into the lungs while food goes into the esophagus.
So the pharynx is a common channel that conducts both air and food. Because of these two functions, the pharynx must open to allow air and food to pass through, and at the same time, it must be able to squeeze and propel the food down into the oesophagus. The pharynx must be able to perform these functions simultaneously at mealtimes. It can do this because, unlike the nose or the windpipe, which are rigid, the pharynx is a soft muscular tube and can squeeze food down during swallowing. Note that the pharynx must channel food without causing choking or aspiration.
Any failure of the above mechanisms can cause breathing, swallowing and voice problems.
The Pharynx as an Airway Organ
Because the pharynx also acts as an airway, an mechanical obstruction of the pharynx can also cause airway obstruction.
There is one type of obstruction that is perculiar to the pharynx. Unlike the nose and the windpipe, which are rigid structures, the pharynx is a soft collapsible tube.
Obstruction can occur even without a physically enlarged structure :
* In an unconscious patient the tongue can fall back to cause obstruction
* An unconscious patient may vomit and the vomitus may go into the lungs because the vocal cords of the unconscious patient do not react to protect the lungs
* During sleep, there is a very common disorder called Obstructive Sleep Apnea (OSA) in which the pharynx collapses repeatedly during sleep.
The Pharynx as a Digestive Organ
As a food channel, the pharynx plays an important part in the beginning of swallowing. As a food bolus is pushed back by the tongue into the pharynx, the nose chamber is sealed by the soft palate so that food does not enter the nose. The pharynx then squeezes the bolus down by muscular contraction. As the bolus passes the voice box, the vocal cords close to prevent choking. At the precise moment when food reaches the opening of the oesophagus, the oesophagus opens and the food is passed down into the stomach. All these actions take place in split seconds. Swallowing is finely controlled by the brain which receives its message from sensory nerves in the pharynx. The brain then directs the soft palate to seal off the nose, the pharynx to contract, the vocal cord to close and the oesophagus to open.
* Failure of the tongue to push the food bolus back means that swallowing cannot be initiated.
* Failure to seal the nose chamber allows food to go into the nose.
* Failure of the pharyngeal muscles to contract results in difficulty in swallowing.
* Failure of the upper oesophagus to open at all or to open at the wrong time causes difficulty in swallowing and choking.
* Failure of the lower esophagus to prevent stomach contents from reaching the pharynx causes reflux
* Failure of the vocal cords to close at the right time causes choking.
Overview - The Larynx
The larynx is commonly known as the voice box. The larynx has a number of important functions.
B) Voice production
C) Protection of the airway from external foreign body
D) Expulsion of contaminants from the lungs
E) Generation of pressure needed for other body functions, such as defecation.
Airway function requires that the vocal cords move away from each other when air is flowing into the lungs, while voice production requires the vocal cords to move toward each other when air is flowing out of the lung. The intact vocal cords can perform these dual functions of airway and voice production because they can automatically open and close the airway as needed. If the vocal cords cannot move away, the patient will have difficulty breathing but can speak. On the other hand, if the vocal cord(s) cannot come together, the patient can breathe but may not be able to speak.
Airway problems can be caused by any mechanical obstruction in the airway.
B) Voice Production
Voice production requires opposite action by the vocal cords. Voice is produced when air is exhaled with the two vocal cords simultaneously coming together, in the mid-line. (For example, you cannot whistle when your lips are not pursed together!)
Hoarseness can be caused by
* Disease of the vocal cords e.g. infection, polyps or tumour (Try sticking something on a guitar string, and notice the change in sound)
* Restricted movement of the vocal cord, e.g. paralysis
* Injury of the vocal cords from overuse, abuse or acid contents from the stomach caused by reflex
C) Protection of the Airway
When food goes down the throat, the vocal cords, helped by other nearby structures, automatically close to prevent choking.
D) Expulsion of contaminants from the Lungs
If you accidentally choke on a piece of food, the lungs expel it. It does this by first compressing the lung air with the vocal cords closed, and when sufficient pressure has been built up, the vocal cords suddenly open and release the pressure, thus expelling the food. Failure of the vocal cords to close reduces this ability to expel.
E) Generation of Abdominal Pressure
In the same way as in function D, the body uses this technique to increase pressure in the abdomen during labour, defecation, or to tense the abdominal muscle wall in martial arts exercises.