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Free STEP1 Exam Braindumps (page: 57)

Page 56 of 213
PDF with 845 Questions

Multiple sclerosis is a relatively common nervous system demyelinating disease. It is autoimmune and restricted to the central nervous system. Nerve conduction velocity is depressed in almost all affected individuals. Manipulations which prolong action potential duration seem to mitigate symptoms, possibly by facilitating conduction through sections of membrane which are no longer myelinated. Application of which type of drug might be expected to prolong action potential duration and thus be a potential therapeutic tool?

  1. activates potassium channels
  2. blocks L-type calcium channels
  3. blocks potassium channels
  4. blocks sodium channels
  5. increases sodium channel inactivation

Answer(s): C

Explanation:

In clinical trials, a class of drugs, the aminopyridines, that blocks certain potassium channels has shown some promise for symptomatic relief of the symptoms of multiple sclerosis. The neuronal action potential is terminated by sodium channel inactivation and potassium channel activation. A drug that blocks potassium channels would thus prolong the action potential. Activating potassium channels (choice A) or increasing sodium channel inactivation (choice E) would shorten the action potential. Blocking sodium channels (choice D) would either shorten the action potential or block it altogether. Since calcium channels are not involved in the neuronal action potential, calcium channel blockade would not be expected to have much effect (choice B).



Which of the following conditions would likely be associated with decreased levels of circulating EPO?

  1. chronic alkalosis
  2. chronic renal failure
  3. emphysema
  4. pernicious anemia
  5. pulmonary fibrosis

Answer(s): B

Explanation:

EPO is a glycoprotein produced primarily in the kidney, thus EPO levels tend to be depressed in chronic renal failure. EPO is a growth factor that stimulates the production of red blood cells. Its production by the kidney is triggered by low tissue oxygenation. Any condition that decreases the oxygen-carrying capacity of the blood (such as anemia, choice D) or that causes hypoxia by decreasing lung function (such as emphysema or pulmonary fibrosis, choices C and E) will produce elevated levels of circulating EPO.
Alkalosis (choice A) increases hemoglobin's affinity for oxygen, making it more difficult for tissues to extract oxygen from the blood. In alkalosis, tissues thus tend to have lower oxygen content, with a resultant increase in circulating EPO levels.



Exhibit:

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

Answer(s): C

Explanation:

Compliance of the lung is the change in lung volume divided by the change in airway pressure (V/P). This patient's lungs have a compliance of 4 L/10 cm O = 400 mL/cm O. Lung elasticity (choices A and B) is the inverse of compliance, and this patient's lungs have an elasticity of 1.25 cm O/L.



Exhibit #1:
Missing
Exhibit #2:

The data in below figure indicate that the lung compliance in this patient (solid line) is altered relative to the norm. This patient is most likely suffering from which of the following conditions?

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

Answer(s): B

Explanation:

Normal lung compliance is about and this patient's lung compliance is significantly higher than normal. High lung compliance occurs in -antitrypsin deficiency. Acute obstruction of the glottis (choice A) does not affect lung compliance. Asbestosis (choice C), sarcoidosis (choice E), and idiopathic pulmonary fibrosis (choice D) are diseases that show a restrictive pattern and would have a compliance less than normal






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