Water and electrolyte handling in GI tract — MCQs

What is the primary mechanism for iron absorption in the duodenum?

A 35-year-old woman presents with exertional dyspnea and fatigue for the past 3 weeks. She says there has been an acute worsening of her dyspnea in the past 5 days. On physical examination, the mucous membranes show pallor. Cardiac exam is significant for the presence of a mid-systolic murmur loudest in the 2nd left intercostal space. A CBC and peripheral blood smear show evidence of microcytic, hypochromic anemia. Which of the following parts of the GI tract is responsible for the absorption of the nutrient whose deficiency is most likely responsible for this patient’s condition?

A 25-year-old man presents to the physician with 2 days of profuse, watery diarrhea. He denies seeing blood or mucus in the stools. On further questioning, he reveals that he eats a well-balanced diet and generally prepares his meals at home. He remembers having some shellfish from a street vendor 3 days ago. He takes no medications. His past medical history is unremarkable. Which of the following mechanisms most likely accounts for this patient’s illness?

A 47-year-old man comes to the physician because of abdominal pain and foul-smelling, watery diarrhea for several days. He has not had nausea, vomiting, or blood in the stool. He has a history of alcohol use disorder and recently completed a 7-day course of clindamycin for pneumonia. He has not traveled out of the United States. Which of the following toxins is most likely to be involved in the pathogenesis of this patient's symptoms?

A 21-year-old man with a recent history of traumatic right femur fracture status post open reduction and internal fixation presents for follow-up. The patient says his pain is controlled with the oxycodone but he says he has been severely constipated the past 4 days. No other past medical history. Current medications are oxycodone and ibuprofen. The patient is afebrile and vital signs are within normal limits. On physical examination, surgical incision is healing well. Which of the following is correct regarding the likely role of opiates in this patient’s constipation?

An investigator is studying the electrophysical properties of gastrointestinal smooth muscle cells using microelectrodes. He measures the resting membrane potential of a cell to be -70 mV. The equilibrium potentials of different ions involved in generating the membrane potential are shown. ENa+ +65 mV EK -85 mV ECa2+ +120 mV EMg2+ +10 mV ECl- -85 mV Which of the following is the most important contributor to the difference between the resting membrane potential and the equilibrium potential of potassium?

Which neurotransmitter primarily mediates slow synaptic transmission in the enteric nervous system?

A 75-year-old woman is brought to a physician’s office by her son with complaints of diarrhea and vomiting for 1 day. Her stool is loose, watery, and yellow-colored, while her vomitus contains partially digested food particles. She denies having blood or mucus in her stools and vomitus. Since the onset of her symptoms, she has not had anything to eat and her son adds that she is unable to tolerate fluids. The past medical history is unremarkable and she does not take any medications regularly. The pulse is 115/min, the respiratory rate is 16/min, the blood pressure is 100/60 mm Hg, and the temperature is 37.0°C (98.6°F). The physical examination shows dry mucous membranes and slightly sunken eyes. The abdomen is soft and non-tender. Which of the following physiologic changes in glomerular filtration rate (GFR), renal plasma flow (RPF), and filtration fraction (FF) are expected?

A 72-year-old male with a past medical history significant for aortic stenosis and hypertension presents to the emergency department complaining of weakness for the past 3 weeks. He states that, apart from feeling weaker, he also has noted lightheadedness, pallor, and blood-streaked stools. The patient's vital signs are stable, and he is in no acute distress. Laboratory workup reveals that the patient is anemic. Fecal occult blood test is positive for bleeding. EGD was performed and did not reveal upper GI bleeding. Suspecting a lower GI bleed, a colonoscopy is performed after prepping the patient, and it is unremarkable. What would be an appropriate next step for localizing a lower GI bleed in this patient?

A 54-year-old man presents with 3 days of non-bloody and non-bilious emesis every time he eats or drinks. He has become progressively weaker and the emesis has not improved. He denies diarrhea, fever, or chills and thinks his symptoms may be related to a recent event that involved sampling many different foods. His temperature is 97.5°F (36.4°C), blood pressure is 133/82 mmHg, pulse is 105/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is notable for a weak appearing man with dry mucous membranes. His abdomen is nontender. Which of the following laboratory changes would most likely be seen in this patient?