Tone of lower esophageal sphincter is increased by?
**Core Concept**
The lower esophageal sphincter (LES) is a critical component of the gastroesophageal junction, functioning as a pressure barrier to prevent reflux of gastric contents into the esophagus. The tone of the LES is influenced by various factors, including hormonal, neural, and mechanical stimuli.
**Why the Correct Answer is Right**
The correct answer involves the regulation of LES tone by gastrin, a peptide hormone secreted by G cells in the stomach. Gastrin stimulates the release of histamine from enterochromaffin-like cells (ECL cells), which in turn activates the H2 receptors on parietal cells. This leads to an increase in gastric acid secretion and a subsequent increase in LES tone, thereby preventing gastric reflux. The gastrin-LES axis plays a vital role in maintaining the integrity of the gastroesophageal junction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the vagus nerve primarily stimulates the contraction of the LES, but it does not directly increase its tone.
**Option B:** This option is incorrect as the presence of food in the stomach can actually relax the LES, increasing the risk of gastric reflux.
**Option C:** This option is incorrect as the presence of a meal in the stomach can stimulate the release of gastrin, but it is the gastrin itself that increases LES tone, not the meal.
**Clinical Pearl / High-Yield Fact**
The LES tone is increased during the day due to the basal release of gastrin and decreased at night due to the absence of gastrin secretion. This nocturnal decrease in LES tone is a contributing factor to the increased incidence of nocturnal gastroesophageal reflux disease (GERD).
**Correct Answer:** D. Gastrin