Answer to Question 1
Normally the lower esophageal sphincter prevents reflux of gastric contents into the esophagus.
This is accomplished by the competence of the sphincter muscle and relative pressures on either side of the sphincter.
If LES competence is compromised or if gastric pressure is greater than esophageal pressure, then gastric contents will flow into the esophagus.
Factors that potentially affect LES pressure include the hormones gastrin, estrogen, and progesterone; presence of hiatal hernia; presence of scleroderma, smoking, or some medications including dopamine, morphine, and theophylline; and nutritional factors.
Foods high in fat, chocolate, spearmint, peppermint, alcohol, and caffeine have been noted to decrease LES pressure.
Answer to Question 2
Parietal cells within the stomach are primarily responsible for synthesis of hydrochloric acid (HCl).
Acid secretion is released in three phases: the cephalic phase, gastric phase, and intestinal phase.
There is also a basal secretion that occurs without any environmental or gastrointestinal stimulation and is controlled by circadian rhythms.
Numerous substances affect parietal cell secretion, including signals to the brain stimulated by our sensory perception of food; presence of food within the stomach; and the substances pepsinogen, acetylcholine, histamine, and gastrin.
Histamine, gastrin, and acetylcholine all mediate the final step in the secretion of HCl.
Atmospheric pressure decreases as altitude increases.
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