A 7-year-old boy with a history of meconium ileus in infancy presents to the pulmonary clinic for a routine follow-up. He has a chronic daily cough producing thick, purulent sputum and has required multiple hospitalizations for respiratory exacerbations. He is currently in the 10th percentile for weight and 15th percentile for height. Sweat chloride testing reveals a concentration of (normal ). The patient's progressive pulmonary disease is driven by a well-described pathophysiologic cascade.
Arrange the following pathophysiologic events in the chronological sequence that leads to this patient's chronic lung disease, starting with the primary cellular defect.
- 1Impaired cyclic AMP-dependent chloride secretion and unregulated sodium absorption
- 2Dehydration of the airway surface liquid layer and thickening of respiratory mucus
- 3Failure of mucociliary clearance and subsequent mucus plugging of distal airways
- 4Endobronchial colonization and chronic infection by opportunistic pathogens
- 5Release of neutrophil elastase and proteases causing permanent structural airway dilation
Cevap
The correct chronological sequence is: (1) Impaired cyclic AMP-dependent chloride secretion and unregulated sodium absorption, (2) Dehydration of the airway surface liquid layer and thickening of respiratory mucus, (3) Failure of mucociliary clearance and subsequent mucus plugging of distal airways, (4) Endobronchial colonization and chronic infection by opportunistic pathogens, (5) Release of neutrophil elastase and proteases causing permanent structural airway dilation.
Cystic fibrosis (CF) lung disease progresses through a predictable pathophysiologic cascade. It begins with the genetic dysfunction of the CFTR channel, leading to defective cyclic AMP-dependent chloride secretion and a lack of inhibition of the epithelial sodium channel (ENaC). This unchecked sodium absorption draws water out of the airway lumen, dehydrating the airway surface liquid (ASL) and creating hyperviscous mucus. The depleted ASL flattens the cilia, resulting in a failure of mucociliary clearance and widespread mucus plugging. These stagnant mucus plugs serve as an ideal nidus for chronic bacterial colonization, initially by Staphylococcus aureus and later by Pseudomonas aeruginosa. The persistent bacterial presence triggers a vigorous, chronic inflammatory response dominated by neutrophils. The continuous release of neutrophil elastase and other proteases degrades the structural elastin and cartilage of the airways, culminating in permanent airway dilation and destruction, known clinically as bronchiectasis.
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Anahtar Kavram
The pathophysiology of cystic fibrosis lung disease follows a sequential cascade starting from a cellular ion transport defect, progressing to mechanical clearance failure, and culminating in chronic infection and structural inflammatory damage (bronchiectasis).