Stages of a Swallow
Eating and drinking belong to the basic necessities of mankind. A healthy adult swallows between 800 and 2400 times a day (1). Although swallowing seems easy, in reality it requires an extremely complicated interaction between various muscles. Timing, coordination, feeling and muscular strength all play a significant role. When one or more of these conditions for swallowing are disturbed, this is called dysphagia. Dysphagia can have a severe social and psychological impact on patients’ life (2).
The normal swallowing process can be divided into the following four phases (1,3):
In this first phase the mouth is opened and a piece of solid food or liquid is taken in. The mouth closes, and with intake of a hard consistency, chewing follows. The cheek muscles are tightened to prevent remnants of food remaining in the cheek pouches. Chewing mixes the food with saliva and prepares it for swallowing. When the chewing process is completed, the food (or bolus) is collected in the centre of the tongue and the person is ready to swallow. This first phase of the swallowing process is entirely voluntary (1).
The second phase in the swallowing process is the transport phase. When the bolus has been collected in the centre of the tongue, the tip of the tongue is placed behind the teeth creating a groove in the tongue. This allows the bolus to slide into the pharynx (the throat). The sliding into the pharynx is not an entirely automatic process. The tongue makes a wave-like movement, thus propelling the food bolus into the back of the mouth. When the bolus reaches certain receptors in the pharynx, the swallowing reflex is triggered. From this point on swallowing is an entirely reflexive action (1,3).
The third phase in the swallowing process is the pharyngeal phase. When the swallowing reflex is triggered, the pharyngeal phase starts. This phase is the most complex phase of swallowing, because it involves many events which occur in a rapid sequence. The soft palate closes the nasopharynx to ensure that the food does not enter the nasal cavity. The vocal folds close and the larynx moves upwards, which results in tilting of the epiglottis and closure of the larynx. This ensures that the food cannot enter the trachea during swallowing. The three pharyngeal constrictor muscles (m. constrictor pharyngis superior, m. constrictor pharyngis medius, m. constrictor pharyngis inferior) contract from top to bottom and transport the bolus into the oesophagus (1,3).
In this last phase of the swallowing process, the bolus enters the oesophagus and is transported further down towards the stomach by peristaltic contractions. In this final phase, the muscles in the neck relax, the larynx is lowered and the vocal folds open, allowing the patient to take a breath (1,3).
1. Matsuo, K., Palmer, J.B. (2008). Anatomy and physiology of feeding and swallowing: normal and abnormal. Phys Med Rehab Clin N Am 19, 691-707.
2. Ekberg, O., Hamdy, S., Woisard, V., Wuttge-Hannig, A., Ortega, P. (2002). Social and psychological burden of dysphagia: its impact on diagnosis and treatment. Dysphagia 17,139-146.
3. Logemann, J. (1999). Evaluation and treatment of swallowing disorders. 2nd ed. Austin: Pro-Ed.