What causes hypertrophic pyloric stenosis?

Hypertrophic pyloric stenosis is caused by progressive hypertrophy of the circular muscles of the pylorus, which leads to a narrowing of the pyloric sphincter. This condition typically occurs in infants and results in gastric outlet obstruction due to the muscular walls of the pylorus becoming excessively thickened. As these muscles hypertrophy, they impede the passage of food from the stomach into the duodenum, causing symptoms such as projectile vomiting and dehydration.

Understanding hypertrophic pyloric stenosis in this context is crucial, as it highlights how the anatomy and physiology of muscle growth in an early developmental phase can lead to significant clinical consequences. The other choices all relate to processes or conditions that do not lead to the characteristic thickening of the pyloric muscle layers seen in this disorder. For instance, thinning of the pyloric sphincter would not cause stenosis, and excessive bile production or increased gastric acid secretion would not directly result in the muscular hypertrophy responsible for the narrowing of the pylorus.