Kliegman RM, Stanton BF, St. Jeme JW, et al: Nelson Textbook of Pediatrics, ed 19, Philadelphia, 2011, Saunders
Wyllie R, Hyams JS, Kay M, editors: Pediatric Gastrointestinal and Liver
Disease, Philadelphia, 2011, Saunders
The Respiratory System
Thida Ong, Amanda Striegl, and Susan G. Marshall 18
Acute and chronic respiratory diseases are common in pediatrics. Children with respiratory problems typically present with symptoms, although abnormal imaging may sometimes precede physical findings. The underlying etiology of childhood respiratory diseases includes the following: genetic (e.g., cystic fibrosis); anatomic (e.g., laryngomalacia); incomplete maturation (e.g., premature birth); iatrogenic (e.g., oxygen toxicity); immunologic (e.g., immune deficiency); infectious (e.g., croup or pneumonia); environmental (e.g., toxins or pollutants); and extrapulmonary (e.g., congenital heart disease). The optimal functioning of the entire respiratory tract allows children not only to survive, but thrive.
Air enters the nose and passes over the large surface area of the nasal turbinates, which warm, humidify, and filter the inspired air. Secretions draining from the paranasal sinuses are carried to the pharynx by the mucociliary action of the ciliated respiratory epithelium. Lymphoid tissue can obstruct airflow through the nasopharynx (adenoids) or the posterior pharynx (tonsils).
The epiglottis protects the larynx during swallowing by deflecting material toward the esophagus. The arytenoid cartilages, which assist in opening and closing the glottis, are less prominent in children than in adults. The opening formed by the vocal cords (the glottis) is V-shaped, with the apex of the V being anterior. Below the vocal cords, the walls of the subglottic space converge toward the cricoid portion of the trachea. In children under 3 years of age, the cricoid ring is the narrowest portion of the airway, whereas in older children and adults it is the glottis. C-shaped cartilage, extending approximately 320° around the airway circumference, supports the trachea and mainstem bronchi. The posterior wall of the trachea is membranous. Beyond the lobar bronchi, the cartilaginous support for the airways becomes discontinuous.
The right lung has three lobes (upper, middle, lower) andcomprises approximately 55% of the total lung volume. The leftlung has two lobes (upper, lower). The inferior division of theleft upper lobe, the lingula, is analogous to the right middle lobe.
The pediatric lung has tremendous capacity for growth. A full-term infant has approximately 25 million alveoli; an adult nearly 300 million alveoli. The growth of new alveoli occurs during the first 2 years of life and is complete by 8 years of age. After this time, lung volume increases primarily by increase in alveolar dimensions, with new alveoli rarely formed.
The major function of the lungs is to exchange oxygen (O2)and carbon dioxide (CO2) between the atmosphere and the blood. The anatomy of the airways, mechanics of the respiratory muscles and rib cage, nature of the alveolar-capillary interface, pulmonary circulation, tissue metabolism, and neuromuscular control of ventilation all influence gas exchange.