GERD and esophageal disordersDownloads

A scientist is studying the mechanism by which the gastrointestinal system coordinates the process of food digestion. Specifically, she is interested in how distension of the lower esophagus by a bolus of food changes responses in the downstream segments of the digestive system. She observes that there is a resulting relaxation and opening of the lower esophageal (cardiac) sphincter after the introduction of a food bolus. She also observes a simultaneous relaxation of the orad stomach during this time. Which of the following substances is most likely involved in the process being observed here?

A 62-year-old man comes to the office complaining of dysphagia that started 4-5 months ago. He reports that he initially had difficulty swallowing only solid foods. More recently, he has noticed some trouble swallowing liquids. The patient also complains of fatigue, a chronic cough that worsens at night, and burning chest pain that occurs after he eats. He says that he has used over-the-counter antacids for "years" with mild relief. He denies any change in diet, but says he has "gone down a pant size or 2." The patient has hypertension and hyperlipidemia. He takes amlodipine and atorvastatin. He smoked 1 pack of cigarettes a day for 12 years while in the military but quit 35 years ago. He drinks 1-2 beers on the weekend while he is golfing with his friends. His diet consists mostly of pasta, pizza, and steak. The patient's temperature is 98°F (36.7°C), blood pressure is 143/91 mmHg, and pulse is 80/min. His BMI is 32 kg/m^2. Physical examination reveals an obese man in no acute distress. No masses or enlarged lymph nodes are appreciated upon palpation of the neck. Cardiopulmonary examination is unremarkable. An endoscopy is performed, which identifies a lower esophageal mass. Which of the following is the most likely diagnosis?