Fourth-year medical students are recruited for a research study assessing their ability to interpret biopsy samples obtained during routine clinical practice. As part of the study, they are given samples of normal respiratory mucosa and asked to identify the cell types present after staining with hematoxylin and eosin. The students observe that the respiratory epithelium changes in composition as the airways continue distally from the trachea to the alveolar ducts. Which of the following features is last to disappear?

Question

Fourth-year medical students are recruited for a research study assessing their ability to interpret biopsy samples obtained during routine clinical practice.  As part of the study, they are given samples of normal respiratory mucosa and asked to identify the cell types present after staining with hematoxylin and eosin.  The students observe that the respiratory epithelium changes in composition as the airways continue distally from the trachea to the alveolar ducts.  Which of the following features is last to disappear?

Quizplus · Accepted Answer

11ec160b_3795_85d4_9249_612ea07078be_MD0001_00 Ciliated mucosal epithelium lines the pulmonary airways from the trachea to the respiratory bronchioles. The airway epithelium gradually changes from pseudostratified ciliated columnar to ciliated simple cuboidal by the level of the terminal bronchioles. Ciliated cells continue to be present through the proximal portions of the respiratory bronchioles, but are not present in the alveolar ducts or in the alveoli themselves. This arrangement is important because cilia function to propel mucus toward the pharynx. The presence of cilia beyond the most distal mucus-producing cells (goblet cells end before the terminal bronchioles) prevents bronchiolar mucus accumulation and airflow obstruction. (Choice A) The rings of hyaline cartilage that encircle the trachea are replaced by cartilaginous plates in the bronchi. These rings and plates help keep the larger airways open and end at the termination of the smallest bronchi (they are not found in bronchioles). (Choice C) Goblet cells are mucus-secreting cells that are present from the trachea down to the larger bronchioles. They are not found within the terminal bronchioles, which are lined by club cells. (Choices D and E) The submucosal mucous glands and serous glands are found from the trachea to the distal-most bronchi and produce mucinous components that help trap inhaled particles. They are not present within the bronchioles. Educational objective: Bronchi have a ciliated pseudostratified columnar epithelium with mucin-secreting goblet cells and submucosal mucoserous glands. The airway epithelium gradually changes to ciliated simple cuboidal by the level of the terminal bronchioles. Bronchioles lack glands and cartilage, and the number of goblet cells decreases distally, ending before the terminal bronchioles. Ciliated epithelium persists up to the respiratory bronchioles.

Fourth-Year Medical Students Are Recruited for a Research Study Assessing