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Obstructive lung diseases: Pathology review
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While doing your rounds, you see two individuals. First is Elsa, a 66-year-old with a history of smoking 2 packs a day for the past 35 years. She came in with progressive shortness of breath and chronic, productive cough, which appeared two and a half years ago but recently got worse. On examination, she presents with pursed-lip breathing, barrel chest, and diminished breath sounds with wheezing. Spirometry was requested, and it showed signs of moderate respiratory obstruction, including an important reduction in forced expiratory volume in one second. The other individual is James, a 7-year-old with a history of wheezing and coughing episodes that began 2 years ago. The episodes used to be only during the winter, but in the past 6 months, they increased in frequency and severity. His father has a history of asthma, and the child himself has eczema. Physical examination and spirometry was normal.
Now, both seem to have some type of obstructive lung disease. But first a bit of physiology. The respiratory tree can be divided into the conducting zone, which consists of large airways like nose, pharynx, larynx, trachea, and bronchi; and the respiratory zone, consisting of respiratory bronchioles, alveolar ducts, and alveoli. Lining the lumen of the airways you’ve got the epithelium, mostly composed of one layer of ciliated pseudostratified columnar epithelial cells up until the beginning of terminal bronchioles, where it is replaced by cuboidal cells.
The ciliated pseudostratified columnar epithelial cells have hair-like projections called cilia. The cilia are responsible for eliminating larger particles like dust that reach the terminal bronchioles by moving them towards the pharynx, where they are coughed out. The epithelium also contains the goblet cell which makes the mucus within the airway. Going deeper past that layer you’ve got the basement membrane and loose connective tissue, called the lamina propria, which together with the epithelium makes up the mucosa. Beyond the mucosa, there is smooth muscle followed by more connective tissue, and together, these two layers make up the submucosa, which is where the bronchial mucinous glands that secrete the majority of the mucus into the lumen of the bronchi live. Finally, in the bronchi, but not the bronchioles, there is a layer of cartilage below the submucosa which stiffens the bronchus and helps to keep it open.
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