USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 661:

  Which of the following compounds directly functions in excitation contraction coupling in smooth but not skeletal muscle?

  A. actin

  B. calcium

  C. myosin

  D. myosin light chain kinase

  E. troponin

  Correct Answer: D

• Question 662:

  In which of the following conditions would the gas composition of both end pulmonary capillary blood and alveolar air approximate that of mixed venous blood?

  A. airway obstruction

  B. breathing 100% oxygen

  C. hyperventilation

  D. normal breathing

  E. pulmonary capillary embolus

  Correct Answer: A

• Question 663:

  Below figure shows pulmonary function test tracings from a healthy person and a patient with pulmonary fibrosis. Of the following measures which would you expect to be increased in this patient, as compared to the expected norms?

  

  A. Forced expiratory volume (FEV)/forced vital capacity (FVC)

  B. FRC

  C. FVC

  D. tidal volume

  E. vital capacity

  Correct Answer: A

• Question 664:

  Although most cases of hypertension are "essential," meaning the underlying disorder is unknown, about 10% of cases are "secondary hypertension" due to a specific, usually treatable cause. Which of the following alternatives can lead to secondary hypertension?

  A. adrenal insufficiency

  B. estrogen deficiency

  C. hyperparathyroidism

  D. renal artery stenosis

  E. volume depletion

  Correct Answer: D

  Section: Physiology A fixed lesion of the renal artery results in impaired perfusion. When the kidney is poorly perfused, it increases renin secretion, which increases blood pressure and thus improves renal blood flow. Hence the appropriate treatment is surgical correction of the renal artery lesion. Adrenal insufficiency (choice A), estrogen deficiency (choice B), and volume depletion (choice E) are situations that tend to diminish blood pressure. There is no clear relationship between hyperparathyroidism (choice C) and hypertension.

• Question 665:

  A patient with untreated diabetes mellitus is admitted to the hospital for treatment. Laboratory findings include a blood pH below 7.2. Which of the following is likely to directly result from this level of acidemia?

  A. arteriolar constriction

  B. decreased catabolism

  C. hyperkalemia

  D. hypoventilation

  E. insulin sensitivity

  Correct Answer: C

• Question 666:

  During a routine preschool examination, a 5-year-old boy is found to have difficulty focusing on distant objects. Which of the following is true during far accommodation of the eyes?

  A. ciliary muscles are relaxed

  B. pupils are constricted

  C. the focal length of the lens is short

  D. the lens is rounded

  E. zonula fibers are relaxed

  Correct Answer: A

  Section: Physiology This patient probably suffers from myopia (nearsightedness). Myopia is either due to eyeballs that are too long or a lens that is too strong. To focus a distant object onto the retina (far accommodation), the lens has to decrease its refractive power (i.e., increase its focal length). This is accomplished through relaxation of the ciliary muscles that oppose the pull of the sclera, resulting in a tightening of the zonula fibers and a flattening of the lens. Shortening of the focal length (choice C), rounding of the lens (choice D), and relaxation of the zonular fibers (choice E), all occur during near accommodation. The pupils also constrict during near accommodation (choice B), perhaps to increase depth of field.

• Question 667:

  Exhibit: *missing*

  In below figure, which point depicts the renal filtered glucose in an 11-year-old male with untreated Type I

  diabetes mellitus?

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: A

  Section: Physiology Type I diabetes mellitus is a condition in which the pancreas secretes inadequate quantities of insulin, causing a fasting hyperglycemia. Choice Adepicts the filtered glucose in such a hyperglycemic state. Choices B and C depict the reabsorbed and excreted glucose which would also occur in a hyperglycemic state. Choice D depicts the filtered and reabsorbed glucose in a fasting, normoglycemic state. Choice E depicts the zero excreted glucose that would occur in a fasting nondiabetic individual since the tubular maximum for glucose has not been exceeded.

• Question 668:

  A 57-year-old woman presents with an arterial pressure of 180/115 mm Hg, and blood creatinine levels are elevated. Renal angiography reveals a severe bilateral stenosis of the renal arteries. Which of the following are elevated also?

  A. ADH secretion

  B. GFR

  C. para-aminohippurate (PAH) clearance

  D. renin secretion

  E. urine output

  Correct Answer: D

  Section: Physiology The bilateral renal artery stenosis will reduce renal perfusion pressure. Hence the juxtaglomerular apparatus will greatly increase renin secretion which causes the large rise in arterial pressure because of the vasoconstrictor action of angiotensin II. A reduced renal perfusion pressure will decrease PAH clearance (choice C), which estimates renal blood flow and will reduce GFR (choice B). The decreased formation of tubular fluid will result in reduced urine output (choice E) and the large rise in arterial pressure will activate arterial baroreceptors and suppress ADH secretion from the posterior pituitary (choice A).

• Question 669:

  In below figure, which point depicts the excreted glucose in a 31-year-old woman with untreated nephrogenic diabetes insipidus?

  

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: E

  Section: Physiology Nephrogenic diabetes insipidus is a condition in which the kidney is insensitive to the normal action of ADH, which is to cause a concentrated urine by promoting water reabsorption in the collecting duct. In such a person, plasma glucose will be normal--around 80 mg/ 100 mL and excreted glucose will be zero, since the tubular maximum for glucose has not been exceeded and all the filtered glucose is normally reabsorbed. Choices A, B, and C depict the filtered, reabsorbed, and excreted glucose in a hyperglycemic state which might occur during diabetes mellitus. Choice D depicts the filtered and reabsorbed glucose in a fasting, normoglycemic state.

• Question 670:

  Apatient is admitted to the hospital following a knife wound to the abdomen which results in extensive bleeding into the abdomen. The arterial pressure at admission is 65/30 mm Hg with a rapid, weak pulse. Compared to normal, the nerve impulses in the carotid sinus nerves and in the sympathetic nerves are changed in what way?

  A. both show decreased nerve impulse rates

  B. both show increased nerve impulse rates

  C. carotid sinus nerve impulses are decreased, sympathetic are increased

  D. carotid sinus nerve impulses are increased, sympathetic are decreased

  E. the patient is unconscious so there are no changes in nerve impulse rates

  Correct Answer: C

  Section: Physiology The carotid sinus baroreceptors signal the magnitude of arterial pressure to the brainstem which then causes reflex inhibition of sympathetic nerves to the body. Thus, a decrease in arterial pressure will cause a reduced carotid sinus nerve impulse rate, which reflexly increases sympathetic nerve impulse rates. Hence, choices A, B, and D are directionally incorrect. Choice E is incorrect because the arterial baroreflexes function at the level of the brainstem, which does not require the conscious mind for its action.