NOSE, MOUTH AND PHARYNX
The nose is the main entrance of the respiratory system: its external portion is particularly showy, projecting anteriorly between the orbits, but its internal portion is notably wider, starting at the nares and ending in the nasopharynx. The inner part of the nose is divided by the nasal septum into two irregularly shaped air chambers known as the nasal cavities, which communicate with the sinuses of the ethmoid, sphenoid, frontal, and maxillary bones through small orifices called ostia and are also connected with the orbits through the lachrymal canals and with the anterior cranial fossa through the olfactory foramina. In a well-conducted study, Xi et al. described the development of the nasal cavities and larynx as well as their air-flow dynamics and aerosol deposition, employing models based on computed tomography (CT) images of 4 children aged 10 days, 7 months, 3 years, and 5 years and comparing the models to a model from a 53-year-old adult (2): the study showed that the nasal cavities rapidly increase in space over the first 5 years of life, when the volume included between the nares and the larynx reaches 40.3% of that of the adult. In this study, the turbinate region, including the 3 turbinate bones located in the lateral walls of the nose, experienced the most noticeable growth during childhood and was undeveloped in both the 10-day-old and 7-month-old models. Moreover, the nostrils were described as smaller and their shape as more circular in the newborn, becoming more oval during infancy and childhood and wedge-shaped in adulthood (2), as shown in previous studies (3). Smaller nares and nasal cavities unavoidably limit the inflow of air, so it is estimated that the nose contributes up to 50% of total airway resistance in younger children. Unsurprisingly, even a mild nasal obstruction due to swelling or mucus production increases the work of breathing in infants and may cause respiratory distress. As far as the paranasal sinuses are concerned, the ethmoidal and maxillary sinuses are already present at birth, while the frontal and sphenoidal sinuses develop later, being radiologically demonstrated by the age of 5-6 years and adolescence, respectively (4). The main feature of the oral cavity in newborns and infants is a larger tongue, which completely occupies a much smaller oral cavity than in subsequent ages (Figure 1 - 2). Moreover, the base of the tongue is in strict connection with the epiglottis, which extends towards the velum. Infants also have a shorter neck, larger head relative to body size and a prominent occiput; as a result, when lying supine, the alignment of the oral, laryngeal and tracheal axes is hampered due to excessive neck flexion, with a high risk of upper airway obstruction and/or difficult visualization of the glottic opening during laryngoscopy. Placing a folded towel roll under the shoulders allows neutral positioning of the neck, improving airway alignment (4, 5). The pharynx belongs to both the respiratory and gastrointestinal tracts and is conventionally subdivided into the nasopharynx, oropharynx and hypopharynx/laryngopharynx. The paediatric pharynx is shorter and has shorter cross-sectional diameters than the adult pharynx. Moreover, the nasopharynx and oropharynx house Waldeyer’s ring, which is composed of the adenoids and the lingual, tubal and palatine tonsils; these lymphatic structures are commonly enlarged in children, since they grow quickly until the age of 5-7 years and then undergo physiological atrophy (4). Studies with magnetic resonance (MR) imaging have shown that this increased mass of lymphoid tissue may contribute to airway obstruction in children (6). Last but not least, the Eustachian tubes open on the lateral wall of the nasopharynx: these structures, connecting the middle ear to the pharynx, are shorter, floppier and more horizontal at birth, facilitating mucus stagnation, and they undergo rapid growth in the first year of life (7, 8).