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Why do you have dysphagia with GERD? - dysphagia more condition_symptoms]dysphagia

I can not imagine in my head. If you have a tumor course you have difficulty swallowing. But do not understand why is dysphagia with acid reflux? If the esophageal muscle does not relax properly? I know that opens the sphincter ERP due to increased pressure in the stomach. Why is dysphagia? Besides, what is the difference between this and stomach ulcer? In the confused.