Federico Villani M24

COORDINATION OF MASTICATION, SWALLOWING AND BREATHING

INTRODUCTION• Basically the pathways for air and food cross in the pharynx• During swallowing the pharynx changes from an airway to a food channel.• During mastication, the food bolus accumulates in the pharynx prior to swallow initiation• Pharynx main functions:

1 Breathing

2 Speaking

3 Mastication

4 Swallowing

INTRODUCTION• Food is collected in pharynx during eating and once chewed is gradually transported through the fauces.

• It’s picked up in oropharynx, where the bolus is formed prior to swallowing.

• Actually, the process depends on physical characteristic of food.

• During swallowing, the pharynx is used only for the food passage and is completely separated from the airway in healthy individuals

PHARYNX ANATOMY• The pharynx is the part of the throat situated inferior to the nasal cavity, posterior to the mouth and superior to the esophagus and larynx.• Is divided in three parts:

① Nasopharynx

② Oropharynx

③ Laryngopharynx• Breathing: Nasal breathing: soft palate is lowered and apposed to the

tongue, dilating the velopharyngeal isthmus. Oral breathing: soft palate elevates to open the fauces,

separating nasal cavity from pharyngeal airway.• Mastication and swallowing: the pharynx becomes the space for bolus aggregation prior to the pharyngeal swallow. During swallowing the pharynx is used only for food passage, it’s separated from the airway.

SEQUENCE FROM MASTICATION TO SWALLOWING

• The normal swallow in humans is described with a four-stage sequential model, which are:

① Oral preparatory: is carried out when we prepare the food bolus biting and chewing, so that it can be trasformed into a homogeneous bolus facilitating swallowing

② Oral propulsive: After preparation, the food will be placed on the tongue, which will engage the hard palate, initiating a wave motion from front to back, to bring the bolus to the back of the mouth. When it touches the anterior pillars, it triggers the swallowing reflex itself.

SEQUENCE FROM MASTICATION TO SWALLOWING

③ Pharyngeal stage: This phase is controlled neurologically by the reticular formation associated with the respiratory center, which determines a central coordination between swallowing and breathing. At this stage the breathing stops for a split second before the soft palate is closed, preventing the passage of the bolus to the nasopharynx; glottis closes epiglottis and vocal cords

④ Esophageal stage: it begins when the bolus passes through the upper esophageal sphincter. The lower esophageal sphincter muscle acts as a valve that opens to allow the passage of the bolus into the stomach.

The relationships among food transport, bolus aggregation, and swallow initiation are modified by the physical characteristics of the food

SEQUENCE FROM MASTICATION TO SWALLOWING

COORDINATION BETWEEN BREATHING AND SWALLOWING

• Swallowing has two essential physiologic aspects:

① passage of food from the oral cavity to the stomach

② airway protection to prevent contamination of the trachea• There are three gate keepers to prevent and avoid tracheopulmonary aspiration: the epiglottis, arytenoids, and vocal folds.• Swallowing and respiration (expiration) have tight temporal coordination in adult humans• The swallow respiratory temporal coordination can change and vary with the conditions of swallowing, including method of ingestion, body position, and food consistency.• Swallow-respiratory coordination varies across the human lifespan (< aged)• The pause in breathing during swallowing is due to inhibition of respiration at neural control centers in the brainstem

COORDINATION BETWEEN BREATHING AND SWALLOWING

COORDINATION BETWEEN BREATHING AND MASTICATION

• Studies reveal that the fauces are open during food processing and triturated food is moved forward to the oropharynx, before swallowing.• Eating solid food alters the respiratory rhythm.• Respiratory frequency (FR) increases during mastication, but decreases with swallowing.• The presence of the food in the pharynx can present a risk for pre-swallow aspiration, if respiration continues and the airway remains open.• Several mechanisms have been proposed: hypothesis that there is an optimal cohesiveness of the food bolus for swallowing that depends on the size of particles and the quantity of saliva

COORDINATION BETWEEN BREATHING AND MASTICATION

DIRECTION FOR FUTURE RESEARCH

• Large gaps remain in our understanding of the neural control of the soft palate and tongue related to breathing and mastication.

• Also in the mechanisms for preventing aspiration during mastication and bolus aggregation.

• Investigations are needed to determine the significance of food remaining in the pharynx for an extended period before swallowing in indivduals with dysphagia (sympton of difficulty in swallowing).

CONCLUSION AND DISCUSSION• Pharynx has an important role in the three phenomena: mastication, breathing and swallowing, which are related each another. • Many studies still work on the mechanismas of inspiration and expiration.• The presence of the food in the pharynx before swallowing is not necessarily abnormal, but it can increase risk of aspiration in dysphagic individuals with poor airway protection.• The main pharynx diseases are

I. Ambiental factors: alcohol.

II. Pharyngitis: inflammation of the throat; can be acute ( short course) or chronic.

REFERENCES • http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2749282/

• http://biology.about.com/library/organs/blpathodigest4.htm

• http://www.breathingcoordination.com/

• http://medical-dictionary.thefreedictionary.com/physiology+of+mastication

• http://www.ncbi.nlm.nih.gov/pubmed/1308667

• http://www.ncbi.nlm.nih.gov/pubmed/16172351

• http://brain.oxfordjournals.org/content/123/9/1863.full