A 2-day-old boy was brought to the intensive care unit from the nursery with tachypnea and hypoxia. The patient was born at 33 weeks, and his mother did not receive prenatal care. Physical examination showed cyanosis. He was intubated but died 2 days later. An autopsy is performed, and a sample of the patient's lung tissue is obtained. Analysis of several large, cuboidal alveolar cells under electron microscopy reveals decreased numbers of granules containing parallel stacks of membrane lamellae. Which of the following pathological processes is most likely to result from the abnormal autopsy findings?

Question

A 2-day-old boy was brought to the intensive care unit from the nursery with tachypnea and hypoxia.  The patient was born at 33 weeks, and his mother did not receive prenatal care.  Physical examination showed cyanosis.  He was intubated but died 2 days later.  An autopsy is performed, and a sample of the patient's lung tissue is obtained.  Analysis of several large, cuboidal alveolar cells under electron microscopy reveals decreased numbers of granules containing parallel stacks of membrane lamellae.  Which of the following pathological processes is most likely to result from the abnormal autopsy findings?

Quizplus · Accepted Answer

11ec160b_3a17_75ef_9249_8b6491434074_MD0001_00 Surfactant, which is produced in type II pneumocytes, works to decrease the surface tension in alveoli, facilitating lung expansion during respiration. When there is insufficient surfactant, as in neonatal respiratory distress syndrome, the result is collapse of alveoli (atelectasis) due to increased surface tension. Surfactant is stored and transported to the cell surface by lamellar bodies (organelles containing parallel stacks of membrane lamellae). It is normally released by exocytosis into the alveolar spaces, where the lamellar contents unravel and spread along the alveolar lining. As it degrades, surfactant is recycled back into the same type II pneumocytes by endocytosis for reprocessing. (Choice A) Emphysema results from excessive activity of intra-alveolar proteases released locally by infiltrating neutrophils and activated alveolar macrophages. (Choice B) Bronchoconstriction can be caused by alveolar hypocapnia, bronchial inflammation, parasympathetic (cholinergic) efferent nerve activity, and inhaled irritants. A deficiency of pulmonary surfactant would not cause bronchoconstriction. (Choice C) Chronic bronchitis manifests as excessive mucus production in the airways and increased inflammatory cells visible in the submucosa. (Choice E) Vasoconstriction of pulmonary arterioles can result from hypoxia secondary to atelectasis. However, actual remodeling of pulmonary vasculature and pulmonary hypertension solely from atelectasis-induced hypoxia are rare. (Choice F) A deficiency of pulmonary surfactant would not be carcinogenic. Educational objective: The lamellar bodies of type II pneumocytes store and release pulmonary surfactant into the fluid layer lining the inner surfaces of alveoli. The major function of surfactant is to reduce surface tension in this fluid layer, and so a surfactant deficiency can cause alveolar atelectasis, as seen in neonatal respiratory distress syndrome. __________ References: Diseases of pulmonary surfactant homeostasis. (http://www.ncbi.nlm.nih.gov/pubmed/25621661) Surfactant therapy for acute lung injury and acute respiratory distress syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/21742216)

A 2-Day-Old Boy Was Brought to the Intensive Care Unit