Final Answer:
The lower esophageal or gastroesophageal sphincter is made up of smooth muscle.Therefore, the correct answer is:A) Smooth muscle
Step-by-step explanation:
The lower esophageal or gastroesophageal sphincter (LES or GE sphincter) is a muscular ring located at the junction between the esophagus and the stomach. Its primary function is to regulate the flow of food and stomach contents between these two structures. The LES prevents stomach acid and contents from flowing back into the esophagus, which helps to prevent acid reflux.
The lower esophageal sphincter is composed of smooth muscle. Smooth muscle is a type of involuntary muscle found in the walls of various organs, including the digestive tract. Unlike skeletal muscle, which is under conscious control, smooth muscle contracts involuntarily in response to various stimuli.
In the context of the LES, the smooth muscle contraction helps maintain a closed state to prevent the backward flow of stomach contents into the esophagus. When you swallow, the LES temporarily relaxes to allow food to pass from the esophagus into the stomach. Afterward, it contracts to prevent the stomach contents, including acidic gastric juices, from refluxing into the esophagus.
Disorders or weakening of the LES can contribute to conditions like gastroesophageal reflux disease (GERD), where stomach acid frequently flows back into the esophagus, leading to symptoms like heartburn and irritation.So the correct option is A.