Certified Neuroscience Registered Nurse (CNRN) Practice Exam

Which structure prevents the backflow of contents from the stomach into the esophagus?

1. Lower esophageal sphincter

2. Pyloric sphincter

3. Cardiac sphincter

4. Fundal valve

The correct answer is: Lower esophageal sphincter

The lower esophageal sphincter serves as a crucial barrier between the stomach and the esophagus, effectively preventing the backflow of gastric contents into the esophagus. This sphincter is a muscular ring located at the junction of the esophagus and the stomach. When functioning properly, it contracts to create a seal that keeps stomach acid and partially digested food from regurgitating into the esophagus, where it can cause irritation and damage, leading to conditions such as gastroesophageal reflux disease (GERD). In contrast, the other structures listed do not play the same role in preventing backflow from the stomach to the esophagus. The pyloric sphincter, for example, regulates the passage of digested food from the stomach into the small intestine, rather than controlling reflux into the esophagus. The term "cardiac sphincter" is sometimes used colloquially to refer to the lower esophageal sphincter, but it is not a distinct anatomical structure. Finally, the fundal valve is not a recognized anatomical structure in the context of esophageal function. Thus, the lower esophageal sphincter is specifically designed to prevent backflow from the stomach, making it the correct choice for this question.