From the time of birth, acquisition of nutrients essential for growth and development of the infant is determined by a complex interplay of hunger, feeding and swallowing skills, and the social environment meeting those nutrient needs. Appropriate interplay results in a mutually satisfying feeding and mealtime experience for both infant and caregiver, reinforcing bonding. A deficit in any of these areas is termed feeding difficulties, or feeding disorder.
Functionally feeding and swallowing are complex processes divided into 4 phases, as shown in Figures 23-1 and 23-2. The first phase is the preoral phase, which is dependent upon the infant/child’s sensation and communication of hunger. The second phase, the oral phase, is the oral cavity–food processing phase where food or liquid is formed into a bolus, enabling safe passage through the pharynx. The next steps in the swallow process are reflexive, and therefore, involuntary. In the ensuing pharyngeal phase, the bolus contacts the tonsillar pillars and pharyngeal wall, resulting in elevation of the larynx, closure of the vocal cords, and relaxation of the esophageal sphincter. Then, contraction of the pharynx deposits the food bolus in the esophagus. During the passage of the food bolus through the pharynx, coordination between breathing and swallowing is essential to prevent aspiration. The final phase, the esophageal phase, moves the food bolus into the stomach and then small intestine, where the processes of digestion and nutrient absorption occur. Any developmental change in the phases of swallowing occurring from infancy through adulthood will impact the ability to feed successfully.
Model of normal phases of swallowing in infants and children. The complexity of interactions between phases often complicates determination of the primary cause of feeding difficulty.
A: The infant oropharynx has anatomical differences from the mature oropharynx. The larynx is elevated with the contact between the epiglottis and soft palate, so that there is a functional separation between air passages (white arrow) and food passages (black/gray arrow) in the pharynx. Food moves around the epiglottis into the pharyngeal recess, and then finally into the esophagus. B: The toddler (aged 2–3 years old) oropharynx. C: The adult oropharynx: (1) oral preparatory phase, (2) oral phase, (3) pharyngeal phase, (4) esophageal phase. The infant oral cavity is much smaller than the toddler or adult oral cavity, thus providing little space for manipulation of the food bolus. The larynx is elevated so that the epiglottis nearly touches the soft palate, and the larynx is at the level of the first to third cervical vertebrae. The tongue is entirely in the oral cavity, with no oral region of the pharynx. In the toddler, the larynx has descended to the fifth cervical vertebra, and by adulthood, to the sixth to seventh cervical vertebrae.