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Free STEP1 Exam Braindumps (page: 64)

Page 63 of 213
PDF with 845 Questions

Exhibit:

Please refer to the exhibit.
Which of the following proteins uses the sodium electrochemical gradient to actively transport a solute into the cell?

  1. A
  2. B
  3. C
  4. D
  5. E

Answer(s): E

Explanation:

SGLT-1 is a sodium-dependent cotransport protein that uses the sodium electrochemical gradient to actively move glucose into the cell. GLUT2 (choice B) does transport glucose, but it is a facilitated diffusion carrier that moves glucose down its concentration gradient. The Na, K-ATPase (choice C) is a primary active transport protein. It uses the energy liberated from ATP hydrolysis to actively transport sodium and potassium. It establishes and maintains the sodium electrochemical gradient. The sodium:
calcium countertransport protein (choice D, also termed NCX) uses the sodium electrochemical gradient to move calcium ions out of, not into, the cell. The calcium ATPase (choice A, also termed PMCA) is a primary active transport protein that actively transports calcium out of the cell. Both NCX and PMCA serve to maintain a low intracellular calcium concentration.



A 23-year-old female has serum electrolytes tested as part of a routine physical. The laboratory results reveal a mild degree of hypokalemia. Which of the following will promote movement of extracellular potassium into the intracellular fluid compartment and cause hypokalemia?

  1. extracellular fluid hyperosmolality
  2. intravenous administration of a betaadrenergic blocker
  3. intravenous administration of insulin
  4. metabolic acidosis
  5. physical exercise

Answer(s): C

Explanation:

Among other actions, insulin is known to stimulate the uptake of potassium into cells of the body via stimulation of the , ATPase. Choices and will either have the opposite action, or no effect.



Below figure shows blood glucose levels after ingestion, at the arrow of 100 grams of glucose in a patient newly diagnosed with Type II diabetes. The curve labeled R is the patient's reference response. After curve R was obtained, the patient commenced a daily exercise regime. After several weeks of exercise a second curve was obtained. Which of the following best describes the response to glucose after exercise training?

  1. curve 1
  2. curve 2
  3. curve 3
  4. curve 4

Answer(s): B

Explanation:

Exercise recruits both non-insulin-dependent and insulin-dependent glucose transport proteins to the plasma membrane of active skeletal muscle cells. This effectively increases sensitivity to insulin and the response to ingested glucose is blunted after exercise training. This excludes choice E, which states that no effect can be expected from exercise and choice A (curve 1), which represents a state of lower insulin receptor sensitivity compared to the sedentary state R. Ingestion of glucose will cause an initial rise of blood glucose in both active and sedentary people (excludes choices C and D).



A deficiency of argininosuccinate synthetase (ASD) can be suspected in a 2448-hour-old neonate with elevated serum ammonia. To discriminate the fact that the hyperammonemia is indeed due to ASD and not due to a deficiency in other urea cycle enzymes, one can assay for the serum concentration of citrulline and urinary orotic acid concentration. Which of the following would best describe the expected findings?

  1. Both citrulline and orotate levels will be low.
  2. Citrulline levels will be absent but orotate will be elevated.
  3. Citrulline levels will be between 100300 M and orotate levels will be elevated.
  4. Citrulline levels will be >1000 M, orotate will be near normal.

Answer(s): D

Explanation:

A urea cycle disorder (UCD) is likely in a neonate that has elevated serum ammonia appearing, not before, but between 24 and 48 hours after a normal term delivery. There are three hallmark symptoms associated with UCDs. These are hyperammonemia, encephalopathy, and respiratory alkalosis. Thus, elevated serum ammonia is not, in and of itself, indicative of a specific defect in the urea cycle. An analysis of the levels of various amino and organic acids in the plasma and urine is the primary key to determining which defect led to the elevation in serum ammonia. Differential diagnosis of neonatal hyperammonemia, as a consequence of a UCD can be accomplished by measurement of plasma citrulline and urinary orotic acid levels. Shown in below figure is the standard differential diagnosis chart for determining which of four possible neonatal UCDs is the cause of the hyperammonemia.
First, the hyperammonemia appears in the absence of any significant acidosis or ketosis. If analysis of serum citrulline demonstrates that it is >1000 M it is confirmation that the clinical symptoms are due to a deficiency in ASD. In this circumstance it is not necessary to assay for levels of urinary orotic acid but they would be expected to be normal. Since citrulline levels are dramatically elevated in cases of ASD, choices A, B, and C are not correct.






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