Anatomy and physiology of feeding and swallowing: normal and abnormal

Abstract

Eating and swallowing are complex behaviors involving volitional and reflexive activities of more than 30 nerves and muscles. They have two crucial biologic features: food passage from the oral cavity to stomach and airway protection. The swallowing process is commonly divided into oral, pharyngeal, and esophageal stages, according to the location of the bolus. The movement of the food in the oral cavity and to the oropharynx differs depending on the type of food (eating solid food versus drinking liquid). Dysphagia can result from a wide variety of functional or structural deficits of the oral cavity, pharynx, larynx, or esophagus. The goal of dysphagia rehabilitation is to identify and treat abnormalities of feeding and swallowing while maintaining safe and efficient alimentation and hydration.

Fig 1. Anatomy lateral view and PA view

Anatomy of the oral cavity and pharynx in (A) the lateral view and (B) posterior view (After Banks et al., 2005, used with permission Two figures from “Atlas of Clinical Gross Anatomy” By Kenneth Moses et al. Elsevier; 2005. ISBN 0323037445 P104, Fig 10.1 Divisions of the pharynx P105, Fig 10.3 Posterior view of the pharynx)

Fig 2. Anatomy of infant and adult

Sagital section of the head and neck in (A) infant and (B) adult human. The food way and the airway are shaded in dark and light grey, respectively. (A) In infant human, the oral cavity is small, the tongue and palate is flatter. The epiglottis is almost attached to the soft palate. The airway and foodway are separated except when swallowing. (B) In adult human, the larynx is lower in the neck, and the food way and airway cross in the pharynx.

Fig 3. Movements of the jaw, hyoid and tongue (A) or soft palate (B) over time

Movements of the jaw, hyoid and tongue (A) or soft palate (B) over time. Vertical positions of (A) the anterior tongue marker (ATM), lower jaw and hyoid bone and (B) soft palate, lower jaw and hyoid bone, each in a complete feeding sequence. Movement towards the top of the figure is upwards. Positions of the structures are plotted relative to the upper jaw over time. Rhythmic movement of the tongue and soft palate is temporally linked to cyclic jaw movement. The hyoid also moves rhythmically; the amplitude of hyoid motion is greater in swallowing than in processing cycles.

Fig 4. VFG images and drawing of stage II transport

Stage II transport: Drawings based on a videofluorographic recording. The tongue squeezes the bolus backward along the palate, through the fauces, and into the pharynx when the upper and lower teeth are closest together and during early jaw opening phase (first three frames). The bolus head reaches the valleculae while food processing continues (last two frames).

Fig 5. the diagram of swallowing a liquid bolus

Normal swallowing of a liquid bolus: Drawings based on a videofluorographic recording. (A) The bolus is held between the anterior surface of the tongue and hard palate, in a “swallow ready” position (end of oral preparatory stage). The tongue presses against the palate both in front of and behind the bolus to prevent spillage. (B) The bolus is propelled from the oral cavity to the pharynx through the fauces (Oral propulsive stage). The anterior tongue pushes the bolus against the hard palate just behind the upper incisors while posterior tongue drops away from the palate. (C-D) Pharyngeal stage. (C) The soft palate elevates, closing off the nasopharynx. The area of tongue-palate contact spreads posteriorly, squeezing the bolus into the pharynx. The larynx is displaced upward and forward as the epiglottis tilts backward. (D) The upper esophageal sphincter opens. The tongue base retracts to contact the pharyngeal wall, which contracts around the bolus, starting superiorly and then progressing downward toward the esophagus. (E) The soft palate descends and the larynx and pharynx reopen. The upper esophageal sphincter returns to its usual closed state after the bolus passes.

Fig 6. VFG and FEES images of bolus entry in the pharynx with two-phase

Eating food with both liquid and semi-solid phases. Selected images from concurrent videofluorographic and fiberoptic recordings of a normal subject consuming corned beef hash and liquid barium. Numbers above the images indicate the time is seconds from start of the recording. Arrows on the images indicate the leading edge of the barium. The liquid component enters (A) the valleculae, (B) hypopharynx and (C) piriform sinus before (D) swallow initiation while the solid phase is being chewed in the oral cavity. There is no laryngeal penetration or aspiration.

Fig 7. Cervical osteophytes

Partially obstructive C6-7 anterior osteophyte (arrow). It impinges on the column of barium, narrowing the lumen by more than 50%.

Fig 8. Sensory impairment with impaired function of the buccal muscles

Food debris retained in the left the buccal sulcus in the mouth due to buccal muscle weakness and sensory deficits caused by a right hemisphere stroke.

Fig 9. Penetration and Aspiration

Videofluorographic images of laryngeal penetration (A) and aspiration (B) in dysphagic individuals swallowing liquid barium. Arrows indicate the leading edge of the barium in the airway.