Children are not small adults, and this fact is particularly true when we consider the respiratory tract. The anatomic peculiarities of the upper airway make infants preferential nasal breather between 2 and 6 months of life. The paediatric larynx has a more complex shape than previously believed, with the narrowest point located anatomically at the subglottic level and functionally at the cricoid cartilage. Alveolarization of the distal airways starts conventionally at 36-37 weeks, but occurs mainly after birth, continuing until adolescence. The paediatric chest wall has unique features that are particularly pronounced in infants. Neonates, infants and toddlers have a higher metabolic rate, and consequently, their oxygen consumption at rest is more than double that of adults. The main anatomical and functional differences between paediatric and adult airways contribute to understanding of various respiratory symptoms and disease conditions in childhood. Knowing the peculiarities of paediatric airways is helpful in the prevention, management and treatment of acute and chronic diseases of the respiratory tract. Developmental modifications in the structure of the respiratory tract, in addition to immunological and neurological maturation, should be taken into consideration during childhood. 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
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