QUESTION: 197

The terminal ileum was removed from a 50-year-old woman during excision of a tumor. About 3 years later, the patient was admitted to the hospital. She is very pale. Hemoglobin is 9 g/dL, MCV (mean corpuscular volume) has increased to 110 (110 fL). The provisional diagnosis is a vitamin deficiency. Which of the following vitamins is the most likely one causing the symptoms?

Answer(s): D

Explanation:

Deficiency of vitamin results in hematological, neurological, and GI effects. The hematologic
symptoms include a low red blood cell count with large-sized macrocytic red blood cells as described. Absorption of vitamin is relatively complicated. The large and not very lipophilic molecule is released from food by the low pH of the stomach and pepsin digestion and binds to R protein (also called haptocorin). Pancreatic proteases digest these complexes and the liberated cobalamin (vitamin ) now complexes with an intrinsic factor (which is produced by gastric parietal cells) and is absorbed as such in the terminal ileum. Hence, vitamin absorption will be low in this patient.
Liver storage is thought to be sufficient for 36 years so that the 3-year latency of the anemia further supports a vitamin deficiency. The water-soluble vitamins and (choices B and C) are
absorbed in the duodenum by simple diffusion. Absorption of the lipid-soluble vitamins A and K (choices A and E) is supported by bile-acid mixed micelles, although vitamin Aand vitamin do not heavily rely on bile acids and can also enter the enterocytes by simple diffusion. Additionally, of the stated choices, only vitamin deficiency is associated with anemia.

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QUESTION: 198

below figure illustrates uptake of two gases (nitrous oxide and carbon monoxide) from alveolar air to pulmonary capillary blood. Based on this information what can we conclude about carbon monoxide?

it does not dissolve in blood
it does not interact with hemoglobin
it has equilibrated with pulmonary capillary blood
it is a diffusion-limited gas
it is a perfusion-limited gas

Answer(s): D

Explanation:

The plot shows that carbon monoxide fails to equilibrate with pulmonary capillary blood during the time that blood is exposed to alveolar air. Since pulmonary partial pressure rises to only a few percent of alveolar partial pressure, carbon monoxide is a diffusion-limited gas. In contrast, nitrous oxide, which does equilibrate, is a perfusion-limited gas (choice E). Carbon monoxide does cross the respiratory membrane (choice C), dissolve in pulmonary capillary blood (choice A), and binds with hemoglobin (choice B). In fact, its affinity for hemoglobin is about 250-fold greater than that of oxygen.

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QUESTION: 199

Which of the following is likely to cause a negative free-water clearance by the kidney?

central diabetes insipidus
demeclocycline, an inhibitor of the renal tubular actions of ADH
nephrogenic diabetes insipidus
water deprivation
water drinking

Answer(s): D

Explanation:

Water deprivation will eventually increase extracellular fluid osmolality, which triggers release of ADH. ADH acts on the collecting duct to increase water reabsorption, thus making the excreted urine more concentrated via a negative free-water clearance. Choices B and C will reduce the sensitivity of the collecting duct to normal circulating ADH. Choices A and E will reduce the amount of ADH secreted by the posterior pituitary.

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QUESTION: 200

An 18-year-old woman presented with 1 week of history of fever and malaise. She had mild jaundice and elevated temperature. Hemoglobin was 13.8 g/dL, leukocyte count 13 × 109 per liter. Serum bilirubin was elevated (42 mmol/L) and contained 95% unconjugated bilirubin. Liver enzyme tests were normal. Which of the following is the most likely cause of these signs and symptoms?

alcohol poisoning
decreased glucuronyl transferase
increased lactate dehydrogenase (LDH)
excessive hemolysis
obstruction of bile flow

Answer(s): B

Explanation:

Glucuronyl transferase is the enzyme that conjugates bilirubin in the liver, after which it is excreted in bile or urine. Ahereditary defect in glucuronyl transferase concentration, or activity, is called Gilbert syndrome. It may lead to mild jaundice and general discomfort with typical onset in childhood or early adulthood. Alcohol poisoning (choice A) leads to liver damage, and an elevation of conjugated bilirubin. Abnormalities of liver enzyme tests would be expected. Lactate dehydrogenase (choice C) catalyzes the conversion of lactate to pyruvate as part of cellular energy production. Since many cells including red blood cells are rich in LDH, increased serum LDH levels could point toward excessive hemolysis, but would not be a cause for it.
Although hemolysis that exceeds the capacity of the liver to clear bilirubin from serum (choice D) would lead to increased unconjugated bilirubin, it is not the best choice due to the woman's normal hemoglobin (1216 g/dL for females). Obstruction of bile flow (choice E) leads to backup of largely conjugated bilirubin in the blood stream.

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QUESTION: 197

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QUESTION: 198

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QUESTION: 199

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QUESTION: 200

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