What condition is the most likely cause of a barrel chest?

A. Mucous obstruction is a secondary effect of cystic fibrosis, but it is not the primary cellular issue. The root cause lies in the dysfunction of chloride transport, which leads to thick, sticky mucus that obstructs various organs.

B. The primary problem in cystic fibrosis is a defect in the CFTR (cystic fibrosis transmembrane conductance regulator) protein, which disrupts electrolyte and water transport across cell membranes. This causes thickened mucus and affects the lungs, pancreas, liver, and intestines.

C. Infection is a common complication in cystic fibrosis due to the buildup of thick mucus, which can trap bacteria, but it is a consequence rather than the primary issue.

D. Pancreatitis is a potential complication of cystic fibrosis due to the blockage of pancreatic ducts, but it is not the major cellular issue.

A. Meconium ileus is a common early sign of cystic fibrosis in newborns. It occurs when the meconium, which is the first stool of a newborn, becomes thick and sticky, leading to a blockage in the intestines. This is often one of the first signs of cystic fibrosis in infants.

B. Cyanosis, while indicative of oxygenation problems, is not a specific sign of cystic fibrosis in newborns. It may be seen in many respiratory or cardiac conditions.

C. Yellow, seedy, loose stools are more commonly associated with normal newborn digestion or conditions like lactose intolerance or gastrointestinal infections, not specifically cystic fibrosis.

D. Coughing is a symptom of cystic fibrosis, but it typically develops later as the disease progresses and affects the lungs, rather than being an early sign in newborns.