Medical case: Fussy child
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Medical case: Fussy child
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[ID] => 554652
[post_author] => 12815
[post_date] => 2024-12-23 18:20:02
[post_date_gmt] => 2024-12-23 23:20:02
[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
A mother brings her two-year-old son to the pediatrician, after noticing that, in recent months, he appears to be “clammy and fussy” a couple of hours after feeding. “He’s vomited a couple of times and I even took him to the ER yesterday because he was having a seizure,” she exclaims, clearly frightened and worried about her son.
During the physical examination, the physician palpates the boy’s abdomen and finds that the boy’s liver is enlarged. She also checks the boy’s growth curve and notices that his weight percentile has fallen from about average to under the 5th percentile. The physician recommends that the boy undergo a carefully monitored fast at the hospital to test for hypoglycemia. After eating a meal, the boy’s blood glucose levels are monitored for several hours. Normal blood glucose levels are 60-150 mg/dL. The results are shown in Figure 1.
Figure 1 Glucose tolerance test results, showing glucose levels following a meal (time = 0)
Upon seeing the results, the pediatrician suggests that the boy is suffering from a metabolic disorder that does not allow him to maintain sufficient blood glucose levels after a meal. She orders that a specimen of the boy’s liver be analyzed for a series of enzyme deficiencies in the metabolism of glucose.
[post_title] => Medical case: Fussy child
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[question] => Which of these statements is most supported by the information given in the passage?
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[answer] => 4
[description] => Reason for Correct Answer:
Normally, after blood sugar levels drop following a meal, glycogen breakdown precedes gluconeogenesis in the maintenance of blood glucose levels.
The passage defines normal blood glucose levels as 60–150 mg/dL.
According to the graph, severe hypoglycemia (< 60 mg/dL) did not occur until 9–10 hours after the meal. (Note that the spike in blood glucose levels at hour = 2 is due to the recent influx of glucose from a meal. The boy’s enzyme deficiency does not affect his ability to break down glucose, but rather, to maintain blood glucose levels.)
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[answers] => Array
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[each_answer] => A. The spike in blood glucose at hour = 2 for the boy is expected because he has a deficiency in an enzyme that prevents him from breaking down glucose.
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[each_answer] => B. Gluconeogenesis is responsible for maintaining blood glucose levels immediately after a meal.
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[each_answer] => C. Glycogen breakdown is responsible for maintaining blood glucose levels 10–18 hours after a meal.
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[each_answer] => D. In this patient, severe hypoglycemia did not occur until 9–10 hours after the meal.
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[1] => Array
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[quiz_unique_key] => 1403770772
[question] => What is a plausible explanation for the boy’s enlarged liver?
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[answer] => 3
[description] => Reason for Correct Answer:
The information in the passage suggests that there is an abnormality in carbohydrate metabolism. What two processes are responsible for maintaining blood glucose levels?
Glycogenolysis and gluconeogenesis are responsible for maintaining blood glucose levels.
Also note that the breakdown of glycogen is probably affected because blood glucose levels start to drop off early after a meal, starting at hour = 5 (Figure 1). If glycogen breakdown was occurring and only gluconeogenesis was affected, we would expect blood glucose to be normal until 10–18 hours after a meal, but the data suggest there may be an impairment in both processes.
The liver is one of the major stores of glycogen – normally, it is broken down after a meal to maintain blood glucose levels. If this is not occurring, glycogen will build up and cause the liver to enlarge.
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[0] => Array
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[each_answer] => A. The liver is engorged because of increased blood flow.
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[each_answer] => B. The liver contains an excess of fat.
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[each_answer] => C. The liver contains an excess of glycogen.
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[each_answer] => D. The liver contains an excess of glucose.
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[quiz_unique_key] => 1403770772
[question] => What would happen to blood glucose levels if the boy was given a snack at Hour = 6
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[answer] => 1
[description] => Reason for Correct Answer:
Why did blood glucose levels rise at hour = 2?
Blood glucose levels rose at hour = 2 in response to a meal at hour = 0.
Since blood glucose rises in response to a meal, we would again expect blood glucose levels to rise initially. However, the boy is unable to maintain blood glucose levels for very long because of an enzyme deficiency, so we would expect the blood glucose levels to drop again after a couple of hours.
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[each_answer] => A. Rise and then drop a couple of hours later
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[each_answer] => B. Rise and continue to rise a couple of hours later
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[each_answer] => C. Rise and then stabilize a couple of hours later
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[each_answer] => D. No change
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[quiz_unique_key] => 1403770772
[question] => The pediatrician diagnoses the patient with an enzyme deficiency that impairs gluconeogenesis and results in a buildup of glucose-6-phosphate inside of the cell. Which of the following is most likely?
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[answer] => 3
[description] => Reason for Correct Answer:
Glucose-6-phosphate is an intermediate in gluconeogenesis. An impairment in the enzyme that breaks it down would result in its buildup in the cell.
Glucose-6-phosphate is also an intermediate in glycolysis. (Choice B is wrong.) However, it is broken down by different enzymes in gluconeogenesis and glycolysis.
Glucose-6-phosphate is also an intermediate in glycogenolysis (glycogen breakdown) AND it’s broken down by the same enzyme in this pathway. (Choice A is wrong.)
In the last steps of both gluconeogenesis and glycogenolysis, glucose-6-phosphate is broken down to glucose by glucose-6-phosphatase, a phosphatase that removes a phosphate group, creating free glucose.
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[each_answer] => A. The enzyme deficiency is not the cause of impairments in glycogenolysis.
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[each_answer] => B. That enzyme’s substrate is not present in glycolysis.
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[each_answer] => C. The enzyme is a phosphatase.
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[each_answer] => D. The enzyme is a kinase.
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[quiz_unique_key] => 1403770772
[question] => Relative to normal patients, what changes in hormone levels are most likely present in this child?
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[answer] => 2
[description] => Reason for Correct Answer:
Insulin and glucagon respond antagonistically to changes in blood sugar. Therefore changes that increase one will decrease the other, and vice versa.
The patient in question has decreased blood sugar levels due to an inability to produce glucose through glycogenolysis and gluconeogenesis.
Insulin acts to promote glucose storage and reduce blood sugar levels, whereas glucagon acts to increase blood sugar levels.
In conditions of low blood sugar, which this boy usually has, glucagon release will be stimulated and insulin release inhibited in an attempt to combat hypoglycemia. This patient will not respond properly to glucagon, but it will continue to be released due to his low blood sugar. The normal effects of insulin and glucagon are summarized below.
https://commons.wikimedia.org/wiki/File:Blood_glucose_control.png
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[each_answer] => A. Increase insulin, decreased glucagon
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[each_answer] => B. Decreased insulin, increased glucagon
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[each_answer] => C. Decreased insulin, normal glucagon
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[each_answer] => D. Normal insulin, decreased glucagon
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Figure 1
