QUESTION: 145

A 34-year-old male is brought into the emergency room, having been found unconscious in his apartment. Apparently, he has been in this state for 2 days. The laboratory values for the patient's blood and urine are consistent with elevated circulating antidiuretic hormone (ADH). Which one of the following will directly stimulate ADH in this patient?

angiotensinogen
extracellular fluid osmolality increase
temperature decrease
thyroid hormone
volume increase

Answer(s): B

Explanation:

ADH acts to increase renal water conservation secondary to dehydration. Choice B, which can result from dehydration, is the logical trigger for ADH secretion. Angiotensinogen (choice A) is inactive and will not directly stimulate ADH, but its active metabolite angiotensin II or III will increase ADH secretion. Choices C, D, and E will either inhibit, or have minimal effects on ADH secretion.

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QUESTION: 146

End-stage chronic renal disease is associated with a glomerular filtration rate (GFR) of less than 15 mL/ min and an increase in which of the following blood values?

calcium
erythropoietin (EPO)
hematocrit
phosphate
1, 25-(OH vitamin

Answer(s): D

Explanation:

Chronic renal failure reduces phosphate excretion and thus phosphate accumulates in the blood. The renal peritubular cells are the major source of circulating EPO, which stimulates red blood cell production. Hence renal failure will decrease EPO levels (choice C) and will decrease hematocrit (choice E) as well. The kidney is responsible for production of vitamin D3, the active
form of vitamin D, and renal failure also results in decreased active vitamin D (choice E). Secondary to this, the circulating levels of calcium will decrease (choice A).

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QUESTION: 147

A very thin 15-year-old female presents with headache, polyuria, and grand mal seizures. She answers the question, if she has had to vomit recently, with "frequently" but that these symptoms "are under control now." Her body mass index is 14.1. Serum glucose, calcium, and potassium are normal. Serum sodium, chloride, and osmolarity are low. As a working diagnosis, which of the following is most likely?

Addison disease
central diabetes insipidus
diabetes mellitus
nephrogenic diabetes insipidus
water intoxication

Answer(s): E

Explanation:

Excessive vomiting can lead to large losses in fluid and electrolytes. Dehydration triggers the sense of thirst. Her age, her extremely low body mass index (normal 18.524.9), and her frequent vomiting all point toward anorexia nervosa. Anorexic people might drink large amounts of water to reach target weight. By drinking a lot of water without adequately replacing electrolyte imbalances, water intoxication can result.
Diluted serum sodium levels can lead to headaches and seizures. Although vomiting, weight loss, and fainting due to low blood pressure could point toward Addison disease, the typical symptoms of hypocortisolism, which include hyperkalemia, hyperosmolality, and hyperpigmentation, are not mentioned and hence make choice A not the best one. In patients with diabetes insipidus, whether caused by a lack of ADH (choice B) or by failure of the kidney to adequately respond to ADH (choice D), serum osmolality is expected to be high. Normal glucose values make uncontrolled diabetes mellitus not the best working diagnosis (choice C).

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QUESTION: 148

The ventricular action potential labeled N in below figure represents a normal ventricular action potential. Which of the other action potentials (labeled AE) would be most characteristic of the ventricular cell after administration of a drug that partially blocks slow calcium channels?

Answer(s): D

Explanation:

The slow calcium channels function in the ventricular myocardial cell to allow the influx of calcium into the cell, which has the dual role of triggering the calcium-mediated contractile mechanism and maintaining the depolarized state after the voltage-gated sodium channels close, soon after the rapid upstroke. Hence, blocking these channels will shorten the plateau phase of the action potential as seen in choice D, while also decreasing the contractile force of the heart. In choice A action potential duration is also shortened, but in a manner that would reflect blockade of the rapid voltagegated sodium channels, not the slow calcium channels. Choice B represents no change in the action potential. Choice C would occur if the drug prolonged the open state of the slow calcium channels. The hyperpolarization of choice E is more likely the result of increased potassium channel currents.

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QUESTION: 145

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QUESTION: 147

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QUESTION: 148

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