A third year medical student is doing research on mechanisms of absorption within the gastrointestinal tract. She is comparing different mechanisms with the hopes of improving drug absorption within the intestines. These mechanisms include simple diffusion, facilitated diffusion, and active transport. Her first group of molecules use simple diffusion to cross from the gastrointestinal tract into the epithelial cells. Which of the following macromolecules can cross the epithelial cell apical membrane by simple diffusion?

A 55 year old woman with a long standing history of osteoarthritis visits the physician because of epigastric abdominal pain, vomiting, fatigue, and weight gain over the past month. The abdominal pain sometimes wakes her at night, and she feel pain if she has not eaten in several hours. She has smoked one pack of cigarettes daily for 20 years. On physical examination, she has epigastric and right upper quadrant tenderness to deep palpation. Bowel sounds are present. A biopsy of the affected tissue is most likely to show hyperplasia of which of the following structures?

A 42 year old mother of five comes to a primary care physician complaining of acute pain in her abdomen that has lasted for 3 days and is most pronounced after meals. Her vital signs are within normal limits, and her body mass index is 34. On physical examination, she has tenderness on palpation with voluntary guarding under the rib cage on her right side. Ultrasound confirms the diagnosis. The patient is counseled regarding surgical options and lifestyle modifications. Which hormone triggers this patient’s pain?

A 34 year old man comes to his primary care physician for his yearly well-patient physical examination. He reports that he “may have developed some reflux lately.” He also states that when he eats certain foods, or has a meal too close to bedtime, he experiences a burning sensation below his sternum and a sour taste in his mouth. His medical history is significant for obesity, hypertension, and hyperlipidemia. He takes lisinopril and simvastatin and reports taking an “occasional” over the counter ranitidine for his gastrointestinal symptoms, typically with near-complete resolution of the symptoms. His physician advises him to continue the use of this medication, as needed. He is also encouraged to lose some weight with diet and exercise. The patient is instructed to return if ranitidine is no longer sufficient to control his symptoms. Which of the following describes the mechanism of action of the medication this patient is taking for his gastroesophageal reflux disease (GERD)?