USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 601:

  A person has an elevated plasma osmolality and reduced plasma ADH level and excretes a large volume of osmotically dilute urine. The urine contains no glucose. What is the most likely explanation for this situation?

  A. congestive heart failure

  B. nephrogenic diabetes insipidus

  C. neurogenic diabetes insipidus

  D. primary polydipsia

  E. uncontrolled diabetes mellitus

  Correct Answer: C

  Section: Physiology Normally, an elevated plasma osmolarity will stimulate increased ADH secretion and cause increased renal water reabsorption, which should lower the elevated plasma osmolarity. Since in this case ADH is reduced in the face of elevated osmolarity and the kidney is not reabsorbing water, it is clear that neurogenic diabetes insipidus is present (choice C). Choice A is incorrect because congestive heart failure will trigger water retention via the reduced cardiac output and lower arterial pressure, which stimulates ADH release via arterial baroreceptors. Choice B is incorrect because nephrogenic diabetes insipidus results from renal insensitivity to normal, or elevated circulating ADH levels. Choice D is incorrect because primary polydipsia is associated with reduced plasma osmolarity which will suppress ADH release. Choice

  E is incorrect because diabetes mellitus will be associated with elevated plasma and urine glucose levels.

• Question 602:

  A 14-year-old female presenting with polyuria is subsequently diagnosed with Type I diabetes mellitus. The polyuria results from an osmotic diuresis that involves primarily which part of the renal tubule?

  A. collecting duct

  B. glomerulus

  C. juxtaglomerular apparatus

  D. proximal tubule

  E. thick ascending limb of the loop of Henle

  Correct Answer: D

• Question 603:

  A 68-year-old woman presents with sleep disturbances and memory loss. After careful analysis, she is diagnosed with early stages of Alzheimer's disease. Her pharmacological treatment plan includes acetylcholine esterase inhibitors. One week after starting treatment, the woman's daughter calls in, reporting that her mom has developed new symptoms that might be related to her new medicine. Which of the following is a likely side effect of the drug?

  A. dry mouth

  B. forgetting to urinate

  C. muscle weakness

  D. nausea and diarrhea

  E. vertigo

  Correct Answer: D

  Section: Physiology Increasing the lifetime of acetylcholine by inhibiting its enzymatic breakdown might help existing brain cells to work better. Studies found that Alzheimer patients at early stages might benefit from cholinergic therapy by small improvements in cognitive abilities and a delay in the progression of the disease. However, the side effects of acetylcholine therapy may outweigh the benefits of it. The increased concentration of acetylcholine at postsynaptic nerve endings of the parasympathetic nervous system can result in excessive stimulation of peripheral organ muscarinic and nicotinic receptors. Increased GI motility may occur resulting in nausea and diarrhea. For the same reason, increased salivation, not decreased as in choice A, and increased micturition, and not decreased as in choice B, are expected. Less common side effects include muscle cramps, not muscle weakness as in choice C, due to overstimulation of the cholinergic neuromuscular junction. Acetylcholine overdosing for an extensive time might eventually lead to muscle weakness due to desensitization of postsynaptic acetylcholine receptors, but this is not the best choice in this case. Vertigo (choice E) is the sensation that the room is spinning. Although neurological problems can always lead to kinetoses, there is no direct connection between acetylcholine esterase inhibitors and vertigo.

• Question 604:

  A 75-year-old male presented with a 6-month history of early satiety and with upper abdominal discomfort for many years. Physical examination revealed mild epigastric tenderness. Esophago-gastroduodenoscopy showed a large, ulcerated mass in the upper stomach, which was found to be cancerous. Surgery resulting in the removal of the gastric fundus was performed. After successful surgery, the patient was advised to eat small portions and to drink small volumes because of which of the following?

  A. almost complete absence of gastric motility

  B. distorted emptying of liquids

  C. inadequate mixing of large food boluses

  D. lack of receptive relaxation in the stomach

  E. weaker and slower propulsion of food toward the pylorus

  Correct Answer: D

  Section: Physiology The receptive relaxation reflex is a feature of the orad stomach, composed of the fundus and upper stomach body. Without food, the orad stomach shows low frequency, sustained contractions that are responsible for generating a basal pressure within the stomach. When food enters the stomach, a reflex is initiated, which allows gastric accommodation of large increases in volume with only small increases in intragastric pressure. The tonic contractions of the orad stomach also contribute to some extent to gastric emptying (choice B), since they generate a pressure gradient from the stomach to the intestine. However, neural and hormonal components play a more important role in regulating gastric emptying, which makes this not the best choice. Since the lower stomach is not affected by the surgery, characteristic motility patterns of the distal stomach remain (choice A). Features of the distal stomach include strong peristaltic waves of contractions, which cause the mixing of the chyme with digestive secretions (choice C), the grinding of the particles to a small size, and the propulsion through the gastroduodenal junction (choice E). All these motility patterns would still be a feature of the remaining stomach.

• Question 605:

  Following an automobile accident a patient suffers a pelvic fracture and significant internal blood loss resulting in hemorrhagic shock. Which of the following organs has the largest specific blood flow (blood flow per gram of tissue) under resting conditions and is especially vulnerable during the shock phase?

  A. brain

  B. heart muscle

  C. kidneys

  D. skeletal muscle

  E. skin

  Correct Answer: C

  Section: Physiology During resting conditions, approximately 15% of the cardiac output goes to the brain, 15% to the muscles, 30% to the GI tract, and 20% to the kidneys. However, when normalized by organ weight, the kidneys receive the largest specific blood flow (400 mL/100 g) at rest and are particularly vulnerable during hemorrhagic shock. The brain (choice A) also receives relatively high specific blood flow (50 mL/100 g). Heart muscle (choice B), not surprisingly, also has a relatively high resting specific blood flow (60 mL/100 g), which may increase fivefold during exercise. Skeletal muscles (choice D) have low specific blood flow (23 mL/100 g) at rest, which may increase up to 20-fold during strenuous exercise. Blood flow through the skin (choice E) varies between 1 and 100 ml/100 g and serves temperature regulation.

• Question 606:

  Opioid peptides are an important physiological mechanism of the body for relief from painful stimuli. Used as pharmacologic agents, they are highly valuable tools for pain management, although side effects are usually inevitable. Which of the following problems are most likely during opiate treatments?

  A. difficulty sleeping

  B. hypermotility of the GI tract

  C. placebo effects

  D. respiratory alkalosis

  E. tolerance (need for higher dosage to achieve the same therapeutic effect)

  Correct Answer: E

  Section: Physiology Tolerance is commonly observed with many pharmacologic agents, including opioids. Difficulty sleeping (choice A), hypermotility of the GI tract (choice B), and respiratory alkalosis (choice D) are opposite to the expected effect of opiates. The placebo effect (choice C) is, at least in part, likely due to the release of endogenous opioid peptides in anticipation of pain relief, but is not a complication or side effect of therapy.

• Question 607:

  Which of the following shows the correct effects of hormones, when increased in serum, on liver glycogen content?

  

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: C

  Section: Physiology Glucagon and catecholamines such as epinephrine stimulate the mobilization of glycogen by triggering the cAMP cascade. Hormones that increase liver cell cAMP promote glycogen breakdown, and hormones that decrease liver cell cAMP promote glycogen synthesis. Cortisol, the main glucocorticoid, regulates the metabolism of proteins, fats, and carbohydrates. It acts on most organs catabolically. However, on the liver it has anabolic effects, increasing glycogen synthesis and accumulation in the liver. Choices A, B, D, and E do not correctly reflect the effects of the three different agents on glycogen metabolism.

• Question 608:

  Exhibit:

  

  Please refer to the exhibit:

  Which of the following is a feature of the principal cell in the cortical collecting duct?

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: D

  Section: Physiology The principal cell is the major sodiumreabsorbing and potassium-secreting cell in the collecting duct. It functions via specific sodium and potassium channels that increase luminal cell membrane permeabilty to these ions and a sodium/potassium ATPase in the basolateral cell membrane. Choice A is incorrect because the specific movement of sodium through the luminal membrane via specific sodium channels creates an excess of negative charges in the tubular lumen. Choice B is incorrect because sodium is reabsorbed while potassium is predominantly secreted by this cell. Choice C is incorrect because aldosterone regulates sodium and potassium transport, not water transport. ADHdoes increase water transport via aquaporins. Choice E is incorrect because a sodium/potassium/2 chloride transporter is not located in this cell type, but is located in the thick ascending loop of Henle cells instead.

• Question 609:

  One of your diabetic patients has a blood glucose level of 200 mg/dL. Surprisingly, a dipstick test is negative for urinary glucose. How could this finding be explained?

  A. dipstick tests are more sensitive for reducing sugars other than glucose

  B. the patient has defective tubular glucose transporters

  C. the patient has diabetes insipidus

  D. the patient has significantly reduced GFR

  E. the patient is in a state of antidiuresis

  Correct Answer: D

  Section: Physiology Glucose excretion by the kidneys depends on the glomerular filtration and tubular reabsorption rates. Glucose first appears in the urine, when the capacity of the glucose transporters in the proximal tubuli cells is exceeded. This usually occurs at plasma glucose levels higher than 180 mg/dL. Patients with longstanding diabetes mellitus often have decreased renal function and reduced GFR. Under these circumstances the threshold (i.e., plasma level) for excretion of glucose is higher than in a healthy person. Urine dipsticks nowadays are both sensitive and specific for glucose, detecting as little as 100 mg/dL (choice A). Earlier dipstick tests were sensitive but not specific (they detected other reducing sugars in addition to glucose). Adefect in glucose transporters (choice B) results in glucosuria even at normal plasma glucose concentration. Patients with diabetes insipidus (choice C) have a large urine output due to absence of ADH or defective renal ADH receptors, but should not have a plasma glucose level of 200 mg/ dL. Antidiuresis (choice E) increases the concentration of solutes in the urine and increases the sensitivity to detect urine glucose. Reabsorption of filtered glucose occurs in the proximal tubule by active transport.

• Question 610:

  As part of a neurological examination, a patient is placed in a chair that rotates to the right under the control of a computer so that the patient's head and body move in unison with the chair. How would a healthy person react immediately upon getting off the chair that turned for 1 minute?

  A. behave the same as before the rotation

  B. display post-rotational eye nystagmus to the right

  C. experience a vertigo that would be diminished if he immediately got back in the rotating chair

  D. experience "past pointing" to the left when asked to reach a target

  E. fall to the left when asked to walk on a straight line

  Correct Answer: C

  Section: Physiology For about 2030 seconds after the rotation stops, the endolymph of the vestibular system continues to rotate due to its inertia. The brain still receives the input of rotation, while the input from the person's eyes and mechanoreceptors signal that the motion stopped. This conflicting information causes dizziness which would disappear if the person continue rotating. The eyes of a healthy person would be "flicking" in the direction opposite to the direction of rotation, so that nystagmus would be to the left, not to the right (choice B). If the person attempts to reach out and touch a target during the postrotatory nystagmus, the movement will miss the target in the direction of the slow phase of nystagmus, to the right in this case, not to the left (choice D). An attempt to walk during the period of nystagmus and vertigo induced by ceasing rotation often leads to a fall, in this case to the right, not to the left (choice E). The compensatory movements to the right are due to the fact that the brain interprets the continuing rotation of the endolymph in relation to the now unmoving outer walls of the vestibular organs as if a rotation to the left has begun. This incorrect input signal is processed by the brain to influence eyes, trunk, and limb muscles to exert compensatory actions. The responses are entirely normal and their absence could indicate dysfunction of the peripheral or central vestibular system (choice A).