|
User: Sign In! Exam: [set] |
| FREE QBank for the USMLE® Step 1 & Step 2 Exams | Create a Test | Submit a Question | Browse Questions | My Account |
Our editorial board has written detailed explanations for every question and we have provided scoring table to crudely estimate your Step 1 score from these sample questions.
1. C is the correct answer.
As skeletal muscle activity increases, the oxygen demand increases. The vascular supply to the area responds by dilating the arterioles in order to bring in more blood and supply the increased oxygen demand. Choice A is incorrect because hydrostatic pressure in the capillaries is increased as blood flow increases. Choice B is incorrect because contracting skeletal muscle will produce metabolites and release them into the capillaries. Choice D is incorrect because contracting muscle cells will take up oxygen from the capillaries. Choice E is incorrect because the vascular supply to the muscle is increased as the arterioles vasodilate, therefore vascular resistance decreases.
2. D is the correct answer.
Ear pain worsened on manipulation, with inflammation of the canal (i.e. external ear) is most consistent with external otitis (D), colloquially known as “swimmer’s ear.” Acute otitis media (A) is an infection of the middle ear that usually presents with earache unaffected by external manipulation, with a red, bulging tympanic membrane on exam. Patients are often febrile to 102 degrees F (38.9 degrees C) or more. Children under 7 are more susceptible to this condition due to their shorter, more horizontal pharyngotympanic (aka auditory or Eustachian) tubes. Bullous myringitis (B) is an infection of the tympanic membrane (TM) itself, in which bubbles filled with blood form on the TM surface. Chronic otitis media (C) is incorrect both because of symptoms inconsistent with otitis media (see above), and the 1-day time course of the complaint is more suggestive of an acute process. Mastoiditis (E) typically manifests with pain, tenderness, and/or swelling of the mastoid process. Further, such a short history of pain is inconsistent with mastoiditis, as it is usually a sequela of otitis media. Accordingly, children (not adolescents) are most frequently affected.
3. C is the correct answer.
In Michaelis-Menten kinetics, halving the amount of enzyme decreases the maximum velocity (Vmax) in half. The Vmax is how quickly a given amount of enzyme can work if provided with unlimited substrate, thus decreasing the amount of enzyme decreases the Vmax. Choices A, B, and D are thus incorrect because the Vmax is not decreased.
4. E is the correct answer.
The key point here is the increase in conjugated bilirubin, demonstrating that the liver is functioning properly. Combined with hepatomegaly, jaundice, bilirubinuria, and the described abnormal stools, this conjugated hyperbilirubinemia suggests an obstruction of the biliary system (E). A defect in cholesterol synthesis (A) could adversely affect bile acid production and result in acholic, loose, clay-colored stools. However, such a defect should not affect bilirubin excretion and thus would not explain the hyperbilirubinemia seen in this infant. Furthermore, these defects in cholesterol synthesis are much less common than obstructions of the biliary system (E). A deficiency of glucuronosyltransferase (B) is suggestive of Gilbert’s syndrome (GS) or the much less common Crigler-Najar syndrome (CDS). However, in GS and CDS the hyperbilirubinemia is due to unconjugated, not conjugated, bilirubin. Unconjugated bilirubin is insoluble, and therefore would not appear in the urine. Hemolysis (C), like the glucuronosyltransferase disorders, results in an unconjugated, not conjugated, hyperbilirubinemia. Again, unconjugated bilirubin would not be seen in the urine. Inflammation of the terminal ileum (D) in an infant with loose, clay-colored stools suggests celiac disease. Though iron absorption (and many other substances) may be affected, celiac disease should not cause hyperbilirubinemia. Crohn’s disease would also affect the terminal ileum and may have symptoms of malabsorption, but it too should not cause hyperbilirubinemia. Further, onset of Crohn’s is usually not seen until 15 – 30 years of age.
5. E is the correct answer.
The interosseous membrane (E) is a fibrous sheet between the radius and ulna, forming the radio-ulnar syndesmosis. It divides the forearm into anterior and posterior compartments, and transmits force from the radius to the ulna. The annular ligament (A) comes off the lateral side of the ulna and encircles the proximal radius. It prevents translation of the proximal radius during pronation, and has no effect on axial forces like the force described here. The bicipital aponeurosis (B), a.k.a. lacertus fibrosus, extends medially from the biceps tendon to reinforce the cubital fossa. It does not transmit force from the radius to the ulna. The flexor retinaculum (C), a.k.a. transverse carpal ligament, forms the roof of the carpal tunnel. It does not transmit force from the radius to the ulna. The intermuscular septum (D) is one of two (lateral or medial) structures arising from the humerus, separating the anterior and posterior compartments of the upper arm. It does not transmit force from the radius to the ulna.
6. A is the correct answer.
Nucleotide deletion in the codon for amino acid 11 (A) would cause a frameshift mutation. Such a mutation could result in a different amino acid at positions 11 and up, with the potential for an aberrant stop codon and early termination, as observed. Nucleotide deletion in codon 20 (B) would cause a frameshift mutation. This mutation may result in a different amino acid 20, perhaps with termination thereafter. However, this option does not explain the difference observed in amino acids 11–19. Nucleotide deletion in the intervening sequence (a.k.a. intron) (C) would not affect peptide sequence because introns are spliced out of the primary transcript, and thus are not translated. Nucleotide substitution in codon 11 (D) may result in a different amino acid 11, but such a substitution would not change the rest of the nucleic acid sequence. Nucleotide substitution in codon 20 (E) may result in a different amino acid 20, but such a substitution would not change the rest of the nucleic acid sequence.
7. B is the correct answer.
Glucose is correct because erythrocytes do not have mitochondria. Accordingly, glucose is their only metabolic energy source, regardless of fasting status. Beta-hydroxybutyrate can be used as a metabolic energy source by muscle or renal cortex tissue after an overnight fast, or by brain tissue in a prolonged fasting state. It is never an energy source for erythrocytes. Free fatty acids can be metabolized by beta-oxidation in the mitochondria of cardiac and skeletal muscle. They are not an energy source for the brain or erythrocytes. During fasting or exercise, pyruvate in the erythrocyte is converted into lactate then shuttled to the liver as part of the Cori Cycle. In other tissues, the mitochondrial enzyme pyruvate dehydrogenase can use pyruvate to generate acetyl-CoA for the citric acid cycle. Triglycerides are the storage form of fatty acids, and are primarily found in the liver and adipose tissue.
8. B is the correct answer.
The tremor described in the question stem is an intention tremor since it is most obvious as the patient's hand moves closer to his target (i.e. his coffee cup), and is not present while at rest. Intention tremors are common in essential tremor, intoxication, multiple sclerosis. They are a sign of cerebellar dysfunction. The cerebellum is split into the vermis and hemispheres. The cerebellar hemisphere (B) regulates the coordination of the ipsilateral extremities and therefore would be involved in an intention tremor. The cerebellar vermis (C) regulates the trunk and midline structures and its dysfunction would cause ataxia (balance problems). Basal ganglia (A) involvement would cause rest tremor like those seen in Parkinson's. Frontal eye field (D) would cause vision problems but not a tremor. Motor nucleus of the thalamus (E) would most likely cause strength deficits, but not a tremor.
9. D is the correct answer.
The bacteria in question is Clostridium difficile (the most common cause of antibiotic-associated diarrhea). C. difficile is a anaerobic gram positive rod that forms spores. These spores are only destroyed by autoclaving (exposure to saturated steam for 15 minutes, option D), because the spore shell is resistant to other forms of sterilization. As a side note, using alcohol based cleaners (like Purell) will not sterilize your hands after you see a patient with C. difficile infection. Therefore, it is important to physically wash your hands with soap and water, in order to mechanically wash the spores off your hands.
10. E is the correct answer.
Due to the vomiting, this woman is losing HCl (the main stomach acid). Since she is unable to control the vomiting and is not eating she cannot adequately compensate for the acid loss. Therefore, she is in a state of metabolic alkalosis (pH>7.40) which eliminates options A, B, and C. Although her kidneys will eventually compensate by excreting HCO3, this process takes about a week to compensate, and therefore HCO3 will be increased (>24). In order to compensate, the respiratory drive decreases so that the body retains more CO2, and therefore pCO2 is increased (>40). Only option E has increased pH, pCO2 and HCO3. Option A is metabolic acidosis Option B is respiratory acidosis Option C is Normal Option D is respiratory alkalosis
11. A is the correct answer.
When the body is stressed, physiologically or pathologically, cortisol (option A) is produced in greater quantities than normal. In this case, severe burns is the stressor which would lead to an increase in cortisol. As a glucocorticoid, cortisol will increase protein catabolism which will increase nitrogen loss. Erythropoietin (option B) is released by the kidneys to stimulate RBC production. Insulin (option C) is released by the pancreas and regulates glucose levels and fat metabolism. Parathyroid hormone (option D) is released by the parathyroid gland and regulates calcium, phosphate and Vit D. Thyroxine (option E) released by the thyroid plays a part in increasing metabolic rate but would not specifically be involved in protein catabolism and thus nitrogen loss.
12. C is the correct answer.
Separation anxiety (option C) is a disorder of childhood that is most often seen in children 7-8 years old. The disorder manifests itself as an overwhelming fear of loss (usually of a parent) and can lead to physical complaints to avoid going to school or other activities. Separation anxiety is a normal part of development which occurs between 8-18 months; however, in a child >5 years old, separation anxiety that affects normal activity is described as a disorder. Childhood schizophrenia (option A) develops before puberty and is presents as withdrawal, failure to develop a separate identity from the mother, and may include autistic like behaviors. Latency is a Freudian stage of development that occurs from about age 6-puberty following the resolution of the Oedipal period. During this period the superego, the moral conscience is formed. Socialized conduct disorder (option D) is is a persistent behavior that manifests as violation of the rights of others (stealing, fighting, malicious acts). In those older than 18 years, this disorder is classified as antisocial personality disorder. Socialized conduct disorder is related to ADHD and ODD (oppositional defiant disorder). Symbiotic psychosis (option E) is classified as a pervasive developmental disorder of early childhood described by Margaret Mahler. Although separation anxiety is feature of the psychosis, it is accompanied by developmental and social retardation.
13. E is the correct answer.
This patient's serum bicarbonate is high, while her potassium is low. The potassium level in her urine is high. (Typical range is 50-150mEq per day). This indicates the use of a diuretic which blocks the reuptake of potassium. Choice A is incorrect because aldosterone increases potassium secretion, therefore aldosterone deficiency would cause decreased potassium secretion. Choice B is incorrect because hyperventilation causes respiratory alkalosis, resulting in decreased bicarbonate in the serum. Choice C is incorrect because acidosis causes decreased potassium secretion. Also, diabetic ketoacidosis would cause additional symptoms and abnormally high blood glucose levels. Choice D is incorrect because ingestion of anabolic steroids generally does not cause the type of potassium imbalance indicated by the lab values.
14. D is the correct answer.
The nucleus involved with circadian rhythms, sleep-wake cycle and melatonin regulation is the suprachiasmatic nucleus of the hypothalamus (option D). Accessory optic nucleus (A) is involved involved in eye movements. The lateral preoptic nucleus (B) is part of heat regulation in the hypothalamus. The pretectal (C) is the area in the midbrain related to pupillary light reflex. The supraoptic nucleus (E) of the hypothalamus regulates water balance and the produces ADH and oxytocin
15. B is the correct answer.
The cells expand in volume when they move from solution X into solution Y, indicating that water enters the cells. This occurs when cells are placed into a hypotonic solution: the level of solute in the cell is higher than in the surrounding solution, and the osmotic pressure created by the solute causes water to move into the cell. Choice A is incorrect because placing cells into a more hypertonic solution would cause them to decrease in volume. Choices C and D are incorrect because placing the cells into a isosmotic or isotonic solution would cause no change in cell volume.
16. C is the correct answer.
There is a one-one relation between the motor neuron and muscle cells (ie one motor neuron for each muscle cell). There is only one active end-plate from each motor neuron per muscle cell; therefore, option D is incorrect. In addition, the action potential in the neuron will be transferred to create a distinct action potential in each muscle innervated by the neuron. The action potential is constant in its duration and in its amplitude; therefore options A and B are incorrect because these parameters cannot be changed. Although the rate of synthesis of acetylcholine would increase the amount released by the axon terminal, the normal amount of acetylcholine released into the neuromuscular junction is enough to excite the muscle cell beyond the action threshold potential. Therefore, increasing the rate of synthesis (option E) would not effect the force of contraction. Increasing the frequency of firing of individual motorneurons (option C) will increase the force of contraction because with each action potential firing in the muscle cell, more calcium enters the cell. Calcium drives the force of contraction and therefore with more calcium in the cell, the stronger the force of contraction will be.
17. E is the correct answer.
In women (especially in the elderly or those with multiple vaginal deliveries), there is tendency for the urogenital diaphragm (E) to weaken causing incontinence due to increase in the abdominal pressure (coughing, sneezing, laughing). Strengthening these muscles (sphincter urethrae muscle (external urethral muscle), deep transverse perineal muscle, superficial transverse perineal muscle and perineal membrane) can often help this incontinence. The detrusor (A) is the muscle around the bladder that helps expel urine by squeezing the bladder. The obturator internus (B) and the piriformis (C) stabilize the hip. The rectus abdominis (D) is muscle of the abdominal wall.
19. B is the correct answer.
The increased pulse and decreased blood pressure indicate a loss of fluid (volume contraction.) The patient's hemoglobin, urea nitrogen, and sodium all rise to above the normal values by Day 3, whereas his glucose and creatinine remain normal. These changes are consistent with an hyperosmotic volume contraction, a loss of water without losing solute. This typically occurs due to dehydration. Choice A is incorrect because renal failure would decrease creatinine clearance. Choice C is incorrect because diabetic ketoacidosis would cause increased blood glucose levels. Choice D is incorrect because gastrointestinal hemorrhage would present with additional symptoms and hemoglobin would decrease. Choice E is incorrect because SIADH would cause decrease in urine volume and retention of fluid, not loss of fluid.
20. A is the correct answer.
In the question stem, the gram positive cocci in clusters are most likely Staph aureus and therefore, the answer choices must pertain to specific attributes of S. aureus. S. aureus expresses protein A which will bind to IgG and fibrinogen receptors (S aureus clumping factor) which will bind fibrinogen (option A) IL-1 and factor VIII (B) are produced by the body and therefore will not identify S aureus. Properdin and platelet factor 3 (C) are related to complement and platelet aggregation. Prothrombin and C3b (D) are related to thrombin (coagulation cascade leading to clot formation) and complement factor part of immune response. Transferrin is a iron carrier in the blood and plasminogen is precursor for plasmin which is an enzyme involved in fibrinolysis (clot busting).
21. B is the correct answer.
The symptoms and histology are typical for diverticulitis, the inflammation of a false pocket (diverticulum) consisting of mucosa and submucosa which have herniated through the muscularis layer. Diverticulitis affects older persons and typically presents with abdominal pain and rectal bleeding. Complications frequently include bowel stenosis, peritonitis, and abscess formation. Choice A, C and D are incorrect because colon tumors typically present as polyps rather than pockets. Choice E is incorrect because volvulus, an abnormal twisting of the intestine which impedes blood flow, typically has a sudden onset and does not display the histology shown here.
22. A is the correct answer.
The description of the bacteria is significant because it identifies the organism as group B streptococcus. Group B strep is a very common causes of newborn meningitis and sepsis, and it is most often found colonizing the mother's vagina (option A). The newborn's GI tract (B) is not completely sterile, but group B strep is not part of the flora. Colonization of the newborn's nasopharynx (C) is incorrect because the infection is not transmitted by the respiratory route, nor is it transplacental infection (D) (For transplacenta think TORCH), nor would it colonize the umbilical cord remnant (E) (an infection here would most likely be from an anaerobic bacteria).
23. C is the correct answer.
The clinical picture suggests a diagnosis of Gaucher’s disease. Gaucher’s disease is the most common variant of a group of diseases called lysosomal storage diseases which are caused by deficiency in any one of many lysosomal enzymes. Gaucher’s disease occurs due to the deficiency of beta-glucocerebrosidase, a lysosomal hydrolase (choice C) that converts glucocerebroside to cerebroside. Glucocerebroside accumulates and can then cause the clinical picture of mental retardation and hepatosplenomegaly. Hormone-sensitive lipase (choice A) is an enzyme found in the cytosol of adipocytes that hydrolyzes triglycerides to free fatty acids and glycerols. Lipoprotein lipase (choice B) is an enzyme found in endothelial cells lining capillaries that hydrolyzes triglycerides circulating in chylomicrons and VLDLs into free fatty acids and glycerols. Sphingolipid synthase (choice D) is an enzyme that uses ceramide as a substrate for sphingomyelin production. Tissue phospholipase (choice E) is an enzyme that hydrolyzes phospholipids into free fatty acids and other lipophilic products.
24. A is the correct answer.
Measles is an enveloped, single-stranded, negative sense RNA virus with a helical nucleocapsid. The hemagglutinin (HA) (choice A) viral protein is an envelope protein that binds sialic acid on cells allowing the virus to be endocytosed. Antibodies targeting viral envelope proteins have the best chance of binding their targets and providing the best immunity. Matrix (choice B), nonstructural (choice C), nucleocapsid (choice D), and polymerase (choice E) proteins are shielded from their respective antibodies by the viral envelop and continue to be hidden once the virus is endocytosed into the host cell. Antibodies to the aforementioned proteins will not provide as much immunity from disease as antibodies to envelop proteins.
25. B is the correct answer.
This patient has heart failure, hypotension, and no signs of atherosclerosis in the setting of alcohol abuse, sedentary lifestyle, and poor dieting. The most likely diagnosis is dilated cardiomyopathy secondary to alcohol abuse. Dilated cardiomyopathy is the most common cardiomyopathy and etiologies include alcohol abuse, thiamine deficiency, coxsackie viral infection, cocaine abuse, doxorubicin toxicity, and idiopathic. Ultimately, patients suffer from systolic dysfunction with eventual cardiac arrest. The most appropriate recommendation for this patient is to remove the source of his cardiomyopathy—alcohol (choice B). Diet (choice C), exercise (choice A & D), and weight loss (choice E) will definitely have cardio-protective effects; however, removing the etiology of the patient’s heart failure needs to have highest priority in the management of this patient.
26. C is the correct answer.
Recent studies have demonstrated that grapefruit juice contains chemicals called furanocoumarins which have been shown to inhibit drug metabolism by interfering with the hepatic cytochrome P450 system, especially CYP3A4. Inhibiting a drug’s hepatic metabolism can lead to higher peak serum concentrations (choice C) of that drug. Hepatic CYP3A4 activity (choice A) would be decreased by the furanocoumarins in grapefruit juice. Intestinal drug metabolism (choice B) should not be affected because grapefruit juice inhibits hepatic drug metabolism. Total body clearance (choice D) and volume of distribution (choice E) of the aforementioned drugs should both decrease. Volume of distribution is the ratio of the amount of drug in the body versus the plasma drug concentration. If the plasma drug concentration increases because drug metabolism is decreased, then volume of distribution will decrease. Clearance is the ratio of the rate of elimination of a drug to the plasma drug concentration. If the plasma drug concentration increases, then clearance will decrease.
27. B is the correct answer.
Finasteride inhibits 5-alpha-reductase, interfering with the conversion of testosterone to dihydrotestosterone (DHT) (choice B). DHT is the primary mediator in the pathogenesis of benign prostatic hyperplasia, causing hyperplasia of glandular and stromal cells. Androstenedione (choice A) is the precursor to both male and female sex hormones. It can be formed from either dehydroepiandrosterone converted by 3-beta-hydroxysteriod dehydrogenase or 17-alpha-hydroxyprogesterone converted by 17,20 lyase. Estradiol (choice C) is the major estrogen in humans. Estradiol can be formed by the aromatization of testosterone. Additionally, androstenedione can be aromatized to estrone (choice D) and then converted to estradiol by 17-beta-hydroxysteriod reductase. Testosterone (choice E) is formed by converting androstenedione via oxidoreductase.
28. B is the correct answer.
Steadily increasing beta-hCG concentration status post removal of hydatidiform mole is suggestive of malignant gestational trophoblastic disease (GTD). Choriocarcinoma (choice B) is a GTD that is commonly associated with increased beta-hCG concentrations and hydatidiform moles, making it the most likely diagnosis in this patient. Adrenal adenoma (choice A) and pituitary insufficiency (choice D) are not commonly associated with either hydatidiform moles or increased concentrations of beta-hCG. Ectopic pregnancy (choice C) or a second noninvasive mole (choice E) could be possible explanations for an increased beta-hCG concentration, but is much less likely than a malignant GTD in this clinical scenario.
29. D is the correct answer.
This patient is exhibiting signs and symptoms of orthostatic (postural) hypotension in the setting of decreased intravascular volume secondary to prolonged diarrhea. Orthostatic hypotension is diagnosed when, within 2-5 minutes of standing, one or more of the following are present: (1) 20mmHg or more fall in systolic pressure; (2) 10mmHg or more fall in diastolic pressure; (3) symptoms of cerebral hypoperfusion. There are many etiologies of orthostatic hypotension which include decreased intravascular volume, autonomic insufficiency, alcohol, medications, and aging. The patient’s prolonged diarrhea has left her in a volume depleted state, causing the apparent signs and symptoms. The best initial therapy for this patient is to replete her intravascular volume with intravenous fluids that are as similar to her plasma as possible. The patient has lost both water and electrolytes in her diarrhea, both of which need to be replaced. Of the answer choices 0.9% Saline (choice D) both resembles plasma the most and is cost-effective. 0.9% Saline is also known as normal saline and is comprised of 154mEq of sodium and 154mEq of chloride. Desmopressin (choice A) is a synthetic arginine vasopressin analogue that has antidiuretic effects. It can be used to treat patients with central diabetes insipidus. This patient most likely has high levels of ADH in her volume deplete state and would benefit more with IV hydration. 5% Dextrose in water (choice B) is a type of IV fluid; however, it is not as physiologically similar to plasma as 0.9% Saline. 5% dextrose in water is essentially water with dextrose without any electrolytes. Furthermore, as the dextrose will be rapidly metabolized, the water supplied distributes across both the extracellular and intracellular fluid compartments. This leads to a reduced amount of intravascular volume repletion relative to supplying saline. Fresh frozen plasma (choice C) is a blood product with strict indications, only given to patients to replace clotting factors, not to correct volume status. Methoxamine (choice E) is an alpha-1-adrenergic receptor agonist that induces vasoconstriction. This patient would benefit more from correcting volume status with IV fluids than with a vasoconstrictor.
30. E is the correct answer.
This patient has a productive cough with unilateral signs of alveolar consolidation as demonstrated by right-sided bronchial breath sounds and increased tactile fremitus. In this clinical setting, lobar pneumonia (choice E) is the most likely diagnosis. Asthmatic bronchitis (choice A) is characterized by a nocturnal cough, episodic expiratory wheezing (inspiratory as well when severe), and decreased breath sounds due to air-trapping. Bullous emphysema (choice B) is characterized by progressive dsypnea, diminished breath sounds, and decreased tactile fremitus due to air trapping. A productive cough is not commonly associated with this condition. Chronic bronchitis (choice C) is defined as a productive cough for at least 3 months for 2 consecutive years. Congestive heart failure (choice D) can lead to bilateral pleural effusions as the pulmonary capillary hydrostatic pressure exceeds the capillary oncotic pressure and fluid moves into the pleural space. Clinically, CHF can be characterized by bilateral decreased breath sounds, crackles at both lung bases, decreased tactile fremitus bilaterally. Fremitus is decreased or absent when the transmission of vibrations from the larynx to the surface of the chest is impaired. Etiologies include obstructed bronchus, COPD, separation of the pleural surfaces by fluid, fibrosis, infiltrating tumor, or a very thick chest wall.
31. D is the correct answer.
Trimethoprim-sulfamethoxazole is a sulfa-based drug. Sulfonamides are known inhibitors of the P-450 enzymatic system, and warfarin is primarily metabolized by CYP450:2C9. Trimethoprim-sulfamethoxazole would be expected to increase the serum levels of warfarin and push the INR to super-therapeutic levels with the increased risk of bleeding. Therefore, it would be recommended to decrease the dosage of warfarin (choice D). Begining therapy with vitamin K (choice A) is the treatment for warfarin overdose, which this patient does not have. Additionally, giving vitamin K will drop the INR to sub-therapeutic levels which will place this patient with a newly placed prosthetic valve at risk for thromboembolisms. Increasing the dosage of warfarin (choice B) would not be recommended in this patient because trimethoprim-sulfamethoxazole will already increase the serum levels of warfarin. Further increasing the dosage of warfarin will definitely place this patient at risk for bleeding. Making no alterations in the dosage of warfarin (choice C) is not recommended because of the risk of bleeding with a supra-therapeutic INR as a result from inhibited warfarin metabolism. Stopping the warfarin and changing to low-dose aspirin (choice E) is not recommended because this patient with a newly placed prosthetic valve still requires anti-coagulation to prevent thromboembolisms. Additionally, aspirin has not been shown to be adequately effective in anti-coagulating patients with prosthetic valves.
32. C is the correct answer.
The deficient enzyme must be common to both pathways of converting glycogen to glucose and of converting fructose to glucose to yield the observed disease. Only Glucose-6-phosphatase (choice C) is common to both pathways. Glucose-6-phosphatase is required in the conversion of Glucose-6-phosphate to glucose, which is the common last step in the pathway of converting both glycogen and fructose to glucose. Deficiency of glucose-6-phosphatase is also known as Von Gierke’s disease or Type I glycogen storage disease. Fructokinase (choice A) converts fructose to fructose-1-phosphate—the first step in the metabolism of fructose. Deficiency in this enzyme should not effect the conversion of glycogen to glucose. Fructokinase deficiency can lead to a benign disorder called essential fructosuria. Glucokinase (choice B) is a liver-specific enzyme that converts glucose to glucose-6-phosphate as the first step of glucose metabolism. Deficiency in this enzyme should not effect conversion of glycogen to glucose or conversion of fructose to glucose. Phosphoglucomutase (choice D) is an enzyme that allows inter-conversion between glucose-1-phosphate and glucose-6-phosphate. Deficiency in this enzyme will impair conversion of glycogen to glucose, but will not impair conversion of fructose to glucose. UDPG-glycogen transglucosylase (choice E) is an enzyme that facilitates the incorporation of glucose into glycogen. Deficiency of this enzyme will impair glycogen synthesis.
33. B is the correct answer.
Mullerian-inhibitory stubstance (choice B) is a hormone secreted by the Sertoli cells of the testes during embryogenesis of the fetal male. It inhibits the development of the Mullerian ducts, which would develop into the upper vagina, uterus and cervix, and fallopian tubes, if uninhibited. Estrogen (choice A and D) and testosterone (choice C and E) have no role in the development of the mullerian ducts.
34. C is the correct answer.
Often when patients refuse to comply with a physician's recommendations, there is a reason for the refusal. It is important to explore the patient's reasons for refusal. This woman has explained why she does not want a mammography. She is afraid of the discomfort involved. Therefore offering analgesia (choice C) is a reasonable first option to try to allay her fears, and have her agree to the procedure. In general, fear tactics (choice A and D), and ultimatums (choice B and E) will not be the correct answer on the USMLE Step 1 exam.
35. E is the correct answer.
This man suffered from Korsakoff syndrome. His history of alcoholism predisposed him to a thiamine (B1) deficiency, a vitamin that is crucial to cellular energy production. A deficiency of this vitamin causes Wernicke-Korsakoff syndrome. Wernicke encephalopathy is characterized by confusion, ocular disturbance, and ataxia of gait. Korsakoff syndrome manifests as loss of short-term memory and confabulation. The lesion of both of these disorders is found in the mammillary bodies (choice E) of the thalamus. The amygdala (choice A) is an almond-shaped nuclear mass in the medial part of the anterior temporal lobe. It is involved in processing memory and emotion. The caudate nucleus (choice B) is a nucleus located in the basal ganglia involved in the control of voluntary movement. The hippocampus (choice C) is a part of the limbic system found in the medial temporal lobe. It is involved in short term memory and and spatial navigation. The locus coeruleus (choice D) is a nucleus located in the brain stem. It is involved in the stress response, and secretes norepinephrine.
36. C is the correct answer.
Gastrin and histamine (choice C) both result in increased HCl secretion from parietal cells. Gastrin is produced by the G cells of the antrum and duodenum, and it stimulates parietal cells, as well as increases histamine release from enterochromaffin cells. Parietal cells also have receptors for histamine, which stimulate them to secrete gastric acid. Acetylcholine will increase gastric acid secretion, but secretin (choice A and E) stimulates secretion of bicarbonate from the pancreas, neutralizing acid. Cholecystokinin (choice B and E) stimulates gallbladder contraction and pancreatic enzyme secretion. Vasoactive intestinal polypeptide (choice D) stimulates water and electrolyte secretion from the intestines via cAMP.
37. E is the correct answer.
Sensitivity, as defined in biostatistics, is the number of true positive results divided by the total positive test results (true positive plus false negative). Sensitivity = 60/(60+20) = 0.75
38. D is the correct answer.
Blood pressures in the pulmonary artery (choice D) are in the range of 15-30mmHg systolic and 4-12mmHg diastolic, which are pressures that most closely match those found in this patient's catheterization. Left atrial (choice C) pressures range from 1-10mmHg, and right atrial (choice E) pressures range from 0-8mmHg. Prior to birth, the ductus arteriosus (choice A) diverts blood from the pulmonary artery to the aorta, and the foramen ovale (choice B) provides a communication between the two atria, equalizing their pressures, and shunting blood from the pulmonary circulation to the systemic circulation.
39. B is the correct answer.
This question involves the relation of predictive value to disease diagnosis. Choosing Point B as the cutoff will cause the test to have a relatively high false-positive rate: some people with concentrations within the normal range will test positive for the disease. However, because this disease is irreversible and fatal unless treated early, it is appropriate in this case to set a cutoff point that will not generate any false-negative results. Thus, setting the cutoff point at B will ensure that the negative predictive value of the test is 100%, at the expense of having a somewhat lower positive predictive value. Choice A is incorrect because the false-positive rate would be so high that the test would not be clinically useful (the positive predictive value will be too low). Choices C-E are incorrect because all these choices would give some false-negative results (the negative predictive value will not be 100%).
40. B is the correct answer.
This infant has the clinical presentation of cystic fibrosis, which is due to defective ion transport at epithelial surfaces (choice B). This is an autosomal recessive disease due to a mutation in the chloride transporter, cystic fibrosis transmembrane conductance regulator (CFTR). Patients present with meconium ileus, deficiencies of pancreatic enzymes, pulmonary obstruction, frequent pulmonary infection, bronchiectasis, cor pulmonale, and respiratory failure. Other findings include liver cirrhosis, infertility, and elevated NaCl concentrations in sweat. This is not due to an autoimmune disorder (choice A), disaccharidase deficiency (choice C), inability to synthesize apolipoprotein B (choice D), or villous atrophy of the jejunum (choice E).
41. B is the correct answer.
Dextrocardia (choice B) is a congenital malformation of the heart in which the heart is situated on the right side of the body. These patients require ECG leads to be placed in the reverse position. The condition is usually asymptomatic. Bifid heart (choice A) is a congenital heart defect where the heart is split, or separated into two parts. Double-outlet right ventricle (choice C) is a congenital heart disease where both the pulmonary artery and the aorta arise from the right ventricle. Persistent truncus arteriosus (choice D) is a cyanotic congenital heart disease where a single arterial vessel arises from the base of the heart, and splits in to the coronary, systemic, and pulmonary arteries. Transposition of the great vessels (choice E) is also a cyanotic congenital heart disease, where the aorta arises from the right ventricle, and the pulmonary artery from the left ventricle. The pulmonary and systemic circuits are in parallel rather than in series.
42. E is the correct answer.
Chloroform and diethyl ether are organic solvents that break down lipid membranes, such as viral envelope (choice E). Enveloped viruses, like HIV-1, acquire their envelopes from the plasma membrane as they exit the cell they infected. This membrane is largely made up of lipids. Naked viruses, like HAV, lack this lipid viral envelope, and are therefore resistant to chloroform and diethyl ether. An important way of classifying viruses is whether or not they have an envelope. The other answer choices do not affect whether the virus is sensitive to organic solvents.
43. C is the correct answer.
Hyperthyroidism (choice C) is often due to excessive production of thyroid hormone in the absence of TSH stimulation. Classic symptoms include irritability, nervousness, weight loss, increased appetite, tremor, sweating, and tachycardia. Congestive heart failure (choice A) is a condition where decreased cardiac output causes inadequate perfusion of tissues. It does not cause irritability. Cushing syndrome (choice B) is any condition that causes excess serum cortisol. Signs and symptoms include weight gain, round face, thinning of skin, purple striae, and hirsutism. Mitral valve prolapse (choice D) is a condition where the mitral valve bulges into the left atrium during systole. It would not cause this man's clinical presentation. Pheochromocytoma (choice E) is a tumor of the adrenal medulla that causes excess secretion of catecholamines, such as epinephrine and norepinephrine.
44. C is the correct answer.
Gap junctions (choice C) allow transfer of chemical and electrical signals between cells. The key structural component of gap junctions is the connexon, a hollow cylinder made up of transmembrane proteins. Gap junctions allow cells to coordinate activities with each other, and are found in nerve cells, cardiac muscle, smooth muscle, and liver cells. Basal lamina (choice A) is a layer of extracellular matrix on which the epithelium sits. Desmosomes (choice B) are structures that bind to intermediate filaments between adjacent cells in order to hold them together. Glycosaminoglycans (choice D) are the carbohydrate portions of proteoglycans, or mucopolysaccharides, that form the major structural components of the extracellular matrix. Tight junctions (choice E) are barriers that form a belt-like structure encircling epithelial cells along their apical surface. They prevent movement of small molecules between the two cells.
46. E is the correct answer.
The urachus is a connection between the dome of the bladder and the umbilicus that obliterates during development. A urachal cyst (Answer E) is usually located in between the obliterated ends of this developmental duct. A hydrocele (Answer A) is a benign collection of peritoneal or scrotal fluid in the scrotum. It is usually due to patent processus vaginalis or scrotal fluid imbalance. A meckel cyst (Answer B), aka duplication cyst, often contains ectopic gastric mucosa. It is most often located in the ileum, duodenum or stomach. A Meckel's diverticulum (Answer C) is an intestinal outpouching that usually occurs in the ileum. It occurs when the vitelline duct, which connects the primary midgut and the yolk sac, fails to obliterate. During the 6th week of development, the midgut herniates through the umbilical cord. An omphalocele (Answer D) occurs during week 12 when this hernation fails to retract, leaving an amnion-covered sac protruding through the umbilicus.
47. B is the correct answer.
Agranulocytosis (Answer B) is a rare adverse effect of all antipsychotics. The RBC (Answer A and E), platelet (Answer C) and eosinophil (Answer D) lines are not known to be affected by clozapine. Clozapine is a (new-generation) atypical anti-psychotic that blocks 5-HT2 and dopamine receptors. Unlike the traditional antipsychotics, it is useful for treatment of the negative symptoms of schizophrenia. Its major side effect is agranulocytosis, which requires WBC monitoring. Haloperidol is a high-potency dopamine blocker used to treat psychosis. Drugs in this class are more selective for dopamine receptors compared to low-potency antipsychotics such as chlorpromazine or thioridazine, hence haloperidol is the drug of choice to avoid cross-reactivity at muscarinic, adrenergic, and histaminic receptors. Long-term adverse effects of haloperidol include parkinsonian features and tardive dyskinesia secondary to blockade of the nigrostriatal pathway.
48. A is the correct answer.
Nasal decongestants are alpha1-adrenergic stimulants that cause smooth muscle contraction, reducing vascular congestion. Benign prostatic hyperplasia is partly due to proliferation of smooth muscle in the bladder neck, urethra, and prostate. Therefore alpha1 blockade is one of the main symptomatic treatments to relieve smooth muscle tension. Main effects of beta2 adrenergic stimulation (Answer B) include bronchodilation and vasodilation. Both sympathetic and parasympathetic ganglionic receptors are nicotinic (Answer C), hence the complex autonomic effects of nicotine. Nicotinic receptor stimulation at the neuromuscular junction (Answer D) causes skeletal muscle contraction, which is not involved in BPH. Serotonergic receptors (Answer E) are not involved in BPH.
49. D is the correct answer.
Always associate mitral stenosis with rheumatic fever. Other valves can be involved but the most common cause of mitral stenosis is aseptic scarring after systemic Group A Streptococcus infection. The murmur of mitral stenosis is described as above. As with any murmur, as the severity increases so does pressure in the chamber before the valve (in this case the left atrium). Dyspnea, fatigue, and rales on exam are symptoms of congestive heart failure, regardless of the underlying cause. This is also the murmur that may be revealed during pregnancy. Aortic regurgitation is a diastolic murmur characterized by wide pulse pressure and may be associated with aortic dissection or trauma. Aortic stenosis usually occurs in elderly patients secondary to calcifications, but it can also be secondary to congenital bicuspid aortic valve in young people. The aortic stenosis murmur is crescendo decrescendo and radiates to the carotids. Mitral regurgitation murmurs are systolic and can occur secondary to chordae tendinae rupture after MI or in predisposed people with mitral valve prolapse. It is a blowing mid to late systolic murmur. Pulmonic regurgitation is a diastolic murmur best heard in the left 2nd intercostal space usually secondary to congenital defect.
49. C is the correct answer.
Muscle atrophy caused by disuse is usually reversible. It is characterized by a decrease in the density of myofibrils (Answer C) but no change in the overall number of muscle fibers (Answer B). Slow-twitch muscle fibers, fast-twitch fibers and intermediate fibers are differentiated cell types, they do not convert after embryogenesis (Answer A). Long-term exercise causes reactive muscle hypertrophy that may include an increase in mitochondrial content (Answer D). Sarcopenia occurs in old age with failure of satellite cells (Answer E) that help regenerate muscle fibers.
49. B is the correct answer.
The closer the toxic dose is to the effective dose, the narrower the therapeutic window. Therefore the ratio of toxic/effective dose is what matters. If it is closer to 1, it has the highest risk of toxicity at effective doses, regardless of what the median effective dose actually is. Examples of drugs that have narrow therapeutic windows include lithium and digoxin.
50. D is the correct answer.
The patient described has multiple myeloma, which is characterized by proliferation of plasma cells and hyperproduction of monoclonal light chains (Bence-Jones proteins). Accumulation at the renal tubules causes renal insufficiency. MM also causes bone destruction, both from marrow expansion and stimulation of osteoclasts. This causes hypercalcemia, which also contributes to renal dysfunction. As with any leukemia, other cell lines are suppressed, causing anemia and thrombocytopenia.
50. B is the correct answer.
Fetal swallowing reduces the amount of amniotic fluid. Congenital gastrointestinal obstructions, such as duodenal atresia (Answer B) cause a buildup of amniotic fluid, or polyhydramnios. Erythroblastosis fetalis (Answer C) occurs when maternal and fetal blood mix, leading to alloimmune hemolysis, usually against Rh antigen. In late pregnancy, most amniotic fluid is composed of fetal urine. Renal anomalies that reduce the amount of urine production, such as horseshoe kidney (Answer D), are associated with oligohydramnios. Congenital heart disease does not manifest until after birth (Answer A). Neural tube defects (Answer E) usually do not affect the amount of amniotic fluid.
50. B is the correct answer.
Self-mutilation is a classic symptom of Lesch-Nyhan syndrome, a genetic HPRT enzyme deficiency. Purines, namely guanine and hypoxanthine, are recycled to GMP and IMP by HPRT (Answer D). A deficiency in HPRT (Answer B) forces purines to be degraded to excess uric acid. Another purine salvage pathway deficiency, APRT deficiency (Answer A), leads to toxic buildup of adenosine metabolites in B and T cells, one of the causes of SCID. Answer C describes nucleic acid recycling, which should prevent uric acid accumulation. PRPP (Answer E) is a purine synthesis enzyme; PRPP superactivity, not deficiency, would cause uric acid buildup.
51. E is the correct answer.
Recall that that the sympathetic nervous system causes pupilary dilation (mydriasis) via α-adrenergics, while the parasympathetic nervous system constrics the pupil (miosis) via muscarinic cholinergics. The diagram in this questions shows that the left pupil is smaller than the right pupil without treatment, which points to either increased parasympathetic stimulation or decreased sympathetic stimulation in the left eye. Adding tyramine, which is an indirect sympathomimetic, has no effect on the left eye, which is consistent with sympathetic denervation of the left eye (choice E). The treatment with epinephrine had a large effect on the left eye, however, which rules out blockade of alpha-adrenergic receptors (choice A), since blocking the α-adrenergic receptors would have blocked any effect of epinephrine. Blockade of β-adrenergic receptors (choice B) is incorrect since B-receptors are not involved in pupillary constriction and dilation. Blockade of muscarinic receptors (choice C) is incorrect because the left eye is constricted without treatment, not dilated as it would be with unopposed sympathetic stimulation. Finally, inhibition of cholinesterase (choice D) is incorrect because it would not have blocked tyramine from dilating the left eye, since it acts on adrenergics, not cholinergics.
52. E is the correct answer.
This patient is most likely taking a statin. Statins inhibit the activity of HMG CoA reductase (choice E). One of the major side effects reported from statin use is myalgia. This is an important presenting symptom because continued use can result in rhabdomyolysis and acute renal failure. Decreasing the production of LDL (choice C) is an effect of statins, but not the direct action. Bile acid binding resins (choice A) such as cholestyramine do not cause myalgias. Decreasing the binding of bile acids (choice B) and decreasing the activity of lipoprotein lipase (choice D) are not current methods for lowering serum cholesterol.
53. D is the correct answer.
This patient most likely has familial hypercholesterolemia, an autosomal dominant disorder associated with a deficiency in LDL receptors (choice D). The rise in his cholesterol concentration is most likely due to a decrease in LDL receptor-mediated endocytosis of cholesterol-rich LDL. Tendon xanthomas are a typical feature of LDL receptor deficiency. In contrast, yellow papular skin lesions, or eruptive xanthomas, are a typical feature of a mutation in the VLDL receptor gene (choice E) and apoC2 (choice B). A mutation in apoA2 (choice A) would interfere with HDL cholesterol and would not lead to skin manifestations. A mutation in apoE4 (choice C) would cause an increase in both triglycerides and cholesterol and there may be yellow deposits in the skin creases on the palms on physical exam.
54. E is the correct answer.
The first thing you need to recognize to answer this question is that this patient has hyponatremia (110 mEq/L, normal is between 135-145). Given the clinical finding of a lung mass, the most likely explanation is that this patient has SIADH, a paraneoplastic complication of small cell carcinoma of the lung (choice E). SIADH is syndrome of inappropriate antidiuretic hormone (ADH) secretion, in which the body, or in this case the lung tumor, secretes ADH that is not responsive to normal feedback mechanisms, resulting in inappropriate retention of water and dilution of the sodium concentration. The other malignancies in the answer choices are not associated with SIADH. Adenocarcinoma of the lung (choice A) is more common in non-smokers and is not associated with SIADH. Craniopharyngioma (choice B) is usually a tumor of childhood that is a remnant of Rathke’s pouch; it could compress the pituitary but this would lead to decreased ADH production, not increased. Medullary carcinoma of the thyroid (choice C) could secrete excess calcitonin, but not ADH. Renal cell carcinoma (choice D) can secrete excess erythropoietin, leading to polycythemia, or excess red blood cells, but this would have no effect on sodium concentration.
55. E is the correct answer.
Inserting a single nucleotide between codons 135 and 136 shifts the reading frame, so that the codons which follow now read: UUU (new codon 136), AUG (new codon 137), UGU (new codon 138), UAA (new codon 139), with a leftover uridine at the end. However, the new sequence includes a stop codon, UAA (new codon 139), which means that the total number of amino acids will be 138 (choice E).
56. E is the correct answer.
Primary spontaneous pneumothorax presents with acute chest pain and shortness of breath. It is believed to result from rupture of a subpleural bleb (choice E), which is usually located in the apex of the lung. Blebs can be found in more than 75% of patients undergoing thoracoscopy for treatment of primary spontaneous pneumothorax. Also, patients with a spontaneous pneumothorax tend to be thinner and taller on average as is the case with this patient. An important distinction of the correct answer from the other answer choices is that it is the only choice that most likely will have an acute presentation in adulthood. Bronchiectasis (choice A) and lung abscess (choice B) are both caused by infectious processes that would be unlikely in a previously healthy patient. Panacinar emphysema (choice C) and pulmonary sequestration (choice D) would both most likely present much earlier in life. Panacinar emphysema is most commonly a result of alpha-1-protease inhibitor deficiency and pulmonary sequestration is a congenital malformation of the lower respiratory tract which results in a nonfunctioning mass of lung tissue.
57. C is the correct answer.
Group B Streptococci, or more specifically S. agalactiae, occasionally colonize the female reproductive tract and are common causes of neonatal meningitis. The best characterized virulence factors of Group B Streptococci are the capsular polysaccharides, which confer serotype specificity. The capsule provides virulence by inhibiting the deposition of complement components on the surface of the organism and therefore inhibiting ingestion (choice C) by cells of the immune system. The other answer choices are examples of virulence factors of other organisms, but not Group B Streptococci.
58. E is the correct answer.
Given this patient's presentation and the finding of curved bacterial rods, the patient is most likely infected with Helicobacter pylori. H. pylori is a major cause of peptic ulcer disease as well as gastritis, both which can cause epigastric pain with a positive fecal occult blood test. H. pylori tests positive for oxidase, catalase, and urease. Therefore, there would most likely be increased urease activity in the antrum (choice E) of this patient. Achlorhydria (choice A) and antiparietal cell antibodies (choice B) both describe changes seen in pernicious anemia. Infection with H. pylori would most likely not cause cholecystitis (choice C) or an immunodeficient state (choice D).
59. G is the correct answer.
Sulfonylureas increase the secretion of insulin from pancreatic beta cells (choice E) by binding to ATP-dependent potassium channels causing an inhibition of the outflux of potassium. This causes a depolarization of the cell membrane, which opens voltage-dependent calcium channels and stimulates secretion of insulin-containing granules. In contrast, sulfonylureas do not decrease the secretion of insulin from the pancreas (choice B). Changing the amount of glucose produced by the liver (choices A and D) is also not the mechanism of action of sulfonylureas. Metformin is an example of a drug that can decrease the amount of glucose produced by the liver. Sulfonylureas also do not decrease the speed of carbohydrate absorption from the intestines (choice C).
60. C is the correct answer.
This patient has regressed (choice C) because she is dealing with her problem in a way a child would, and she has therefore set back her maturational clock. This defense mechanism is seen in very sick patients as well as in children under stress who may begin wetting the bed. Denial (choice A) is the avoidance of awareness of some painful reality, such as the denial of a newly diagnosed cancer. Displacement (choice B) is a process whereby avoided ideas and feelings are transferred to some neutral person or object. An example of this is a wife yelling at her husband because she is angry at her boss. Repression (choice D) is an involuntary withholding of conscious awareness. Sublimation (choice E) is the only mature defense mechanism listed in the answer choices, involving replacement of an inappropriate desire with a desire or action that is considered appropriate, differing from displacement where the desire is replaced or transferred, but to a person or object that is still inappropriate. An example of sublimation would be a person who utilizes they're frustration or anger as competitiveness in sports.
61. A is the correct answer.
Granulocyte colony-stimulating factor (choice A) increases neutrophil, eosinophil and basophil counts: the patient’s white blood cell differential shows an increase in the percentage of neutrophils from 9% to 90% after the growth factor was given. The percentage of eosinophils did not change, but since the total number of cells increased, the absolute eosinophil amount also increased. The percentage of lymphocytes decreased. The other growth factors listed would not increase production of neutrophils. Transforming growth factor-beta (choice B) is made by macrophages, endothelial cells, and T-cells and is involved in B-cell maturation. IL-6 (choice C) is an acute phase reactant made by macrophages, and IL-8 (choice D) is involved in neutrophil migration and chemotaxis. Macrophage colony-stimulating factor (choice E) would increase the percentage of cells in the monocyte-macrophage line, but that information is not provided in the question.
62. B is the correct answer.
Point Y shows an elevated pCO2, but the pH is slightly below normal, indicating that the patient has compensated and is thus experiencing a chronic acid/base imbalance. In chronic obstructive pulmonary disease (choice B), patients retain CO2 and thus are in a state of chronic respiratory acidosis; the renal compensation is to retain bicarbonate and secrete H+ to correct the pH. Adaptation to high altitude (choice A) would lead to a higher than normal pH, as a person would try to breathe in more oxygen would hyperventilate, blowing off CO2 and become alkalotic. In diarrhea (choice C), the patient experiences metabolic acidosis, but the respiratory compensation would lower the pCO2, not raise it. Similary, in the case of ingestion of a strong acid (choice D), the patient would hyperventilate to blow off CO2 to compensate for the metabolic acidosis, lowering the pCO2, not raising it. Severe prolonged vomiting (choice E) leads to loss of acidic gastric contents which would lead to a metabolic alkalosis – since the body never “over-compensated” an acidic pH in the face of metabolic alkalosis is unlikely even with respiratory compensation, and especially not in an acute setting.
63. C is the correct answer.
Antimicrobial resistance in Escherichia coli is primarily conferred through transfer of a plasmid (choice C). This is true in the case of strains of Excherichia coli that carry a resistance to ampicillin. Without the need to produce the beta-lactamases needed to be resistant to ampicillin, it will not preferentially transfer the plasmid and it may be lost in subsequent generations. The other four answer choices discuss changes to the actual gene which are not ways in which E. coli develops resistance.
64. A is the correct answer.
Haemophilus decreyi (choice A) is a Gram-negative coccobacillus that is typically grown on chocolate agar. Like the other answer choices, it is a sexually transmitted disease, but it is characterized by painful lesions in the genitalia. Herpes simplex virus (choice B), like other viruses, cannot be Gram stained. The test of choice for identifying a herpes virus is a Tzanck test. Neisseria gonorrhoeae (choice C) is a Gram-negative diplococci. Treponema pallidum (choice D) is the bacteria that causes syphilis and is a spirochete. Trichomonas vaginalis (choice E) parasitic flagellated protozoan.
65. E is the correct answer.
Selective constriction of the efferent arterioles will cause the changes described in choice E. It will increase GFR by causing an increase in the glomerular capillary pressure causing an increase in the net pressure in the glomerulus. There will also be decreased renal blood flow as constriction of either the afferent or efferent arterioles will cause a decrease in perfusion to the kidneys. As the filtration fraction is the GFR devided by renal plasma flow, which is effectively renal blood flow, this number will increase as GFR has increased and renal blood flow has decreased. The other choices give an incorrect combination of answers.
66. D is the correct answer.
ADH (vasopressin) is secreted by the posterior pituitary gland. Its secretion is in response to either activation of baroreceptors in the veins, atria and carotid bodies in response to reduced plasma volume, or by activation of osmoreceptors in the hypothalamus in response to increased plasma oncotic pressure. The patient in this question has orthostatic hypotension and poor skin turgor, clinical signs suggesting volume depletion. Likewise, plasma volume is low and ADH levels are responsively increased. Because plasma sodium concentration is lower than normal, the renin-angiotensin-aldosterone system will be activated and the concentrations of all three will be increased. ANP is secreted by atrial myocetes in response to increased blood pressure, the opposite of this patient. In dehydrated states, urine osmolality is higher than plasma/serum osmolality due to the action of ADH increasing permeability of the collecting duct to reabsorb water.
67. C is the correct answer.
This patient is exhibiting signs of Wernicke's encephalopathy, a condition of thiamine deficiency. The classic triad of Wernicke's is encephalopathy, ophthalmoplegia in the form of lateral gaze nystagmus, and ataxia. Chronic alcoholics and indivduals undergoing TPN without B1 supplements are predisposed to B1 deficiency. Wernicke's may be precipitated by carbohydrate heavy meals because thiamine is a cofactor for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, key enzymes in glucose metabolism. Untreated Wernicke's encephalopathy may progress to Korsakoff syndrome, an irreversible condition characterized by psychosis, anterograde and retrograde amnesia, and confabulation.
68. C is the correct answer.
Cytomegalovirus (CMV) infection in immuncompetent hosts is usually subclinical, or at most presents as a mild form of mononucleosis similar to Epstein-Barr virus with mild fever, lymphadenopathy, splenomegaly and atypical circulating lymphocytes for several weeks. However, in immunocompromised hosts, such as the post-transplant patient above, CMV infection or reactivation of a latent CMV infection can manifest as a multisystem disease within 20-60 days. In addition to the aforementioned features of mononucleosis, CMV in immunocompromised hosts also manifests as pneumonia, hepatitis, gastritis and colitis. In late stage AIDS patients, CMV particularly causes a severe form of retinitis. Adenovirus also causes a worsened form of its normal disease in immunocompromised hosts, but usually presents with severe gastroenteritis (vomiting and diarrhea) and pneumonia/bronchitis/ARD. Coxsackie virus usually presents in childhood as hand-foot-and-mouth disease, causing painful, vesicular, blisters in the oral mucosa, tonsillar pillars and palms and soles. Though influenza may cause a severely fatal pneumonia in immunocompromised hosts, it does not cause usually cause liver abnormalities. Parvovirus usually causes a chronic infection of the bone marrow and should be suspected in post-transplant patients with erythropoietin-resistant anemias.
69. E is the correct answer.
Between the ages of 7-9 months, an infant develops stranger anxiety for individuals who are not primary caregivers. Stranger anxiety is a normal developmental milestone. It manifests as crying and physical discomfort when not in the presence of a primary caregiver, and usually resolves by 24 months. It is commonly confused with the pathologic entity of separation anxiety disorder, a condition usually seen beyond the age of two years and classified as three or more of the following DSM-IV criteria: - Recurring distress when separated from the subject of attachment (such as the mother or home) - Persistent, excessive worrying about losing the subject of attachment - Persistent, excessive worrying that some event will lead to separation from a major attachment - Excessive fear about being alone without subject of attachment - Persistent reluctance or refusal to go to sleep without being near a major attachment figure, like a mother - Recurrent nightmares about separation
70. B is the correct answer.
When the USMLE question involves a traveler returning to a trip from a specific locale, it is usually a clue to the diagnosis. In this case, coccidiomycosis is a well-known fungal disease endemic to California, Arizona, New Mexico and Nevada, giving it the moniker "Valley fever." It usually presents several weeks after exposure as a flu-like illness with fever, myalgias and erythema nodosum over the shins. Patients who fail to clear the infection may progress to chronic pulmonary infection, pulmonary effusions or meningitis. Blastomycosis and Histoplasmosis are also systemic fungal infections, but the travel history usually involves a recent visit to the Mississippi/Ohio River valley. M. pneuomniae causes a pneumonia syndrome, and M. marinum causes systemic skin nodules, but both are usually opportunistic infections of the immunocompromised.
71. D is the correct answer.
17 beta-estradiol is the major form of estrogen present in a woman's body from menarche to menopause. Its role in menstruation is primarily during the proliferative phase (day 1-14) to increase the size of the endometrium and prepare it for the progesterone-dominated secretory phase (day 15-28) during which an embryo will potentially implant and spiral vessels will penetrate the layers of the endometrium. Estradiol peaks on day 13, and a surge of positive feedback on luteinizing hormone (LH) by estradiol during this period causes the follicle to burst on day 14 of the cycle, releasing the egg. Progestone levels are at their lowest during this period, and it is only the secretion of progesterone by the remnants of the follicle, the corpus luteum, that causes a rise in progesterone levels in the second phase of the cycle.
72. A is the correct answer.
This patient is exhibiting signs of upper and lower motor neuron degeneration, suggesting a diagnosis of amyotrophic lateral sclerosis (ALS). Upper motor neuron degenerative signs include hyperreflexia, increased tone, and positive bilateral Babinski signs. Lower motor neuron degenerative signs include muscle atrophy, areflexia, fasciculations, and flaccid paralysis. Since ALS causes degeneration of both upper and motor neurons, this is the likely diagnosis for this patient. Alzheimer dementia is not known to correlate with motor neuron loss. Guillan-Barre is usually post-viral illness of the GI tract and usually presents with a rapidly ascending, reversible muscle paralysis. Multiple cerebral infarcts would explain the upper motor signs but not the degeneration of lower motor neurons. Multiple sclerosis usually presents in middle-aged women with optic signs or singular neurologic defects that include peripheral sensory losses, not the universal loss of motor neurons described above.
73. C is the correct answer.
This patient is having an immune complex (type III) hypersensitivity reaction to the tetanus booster commonly referred to as an Arthus reaction. Because the patient has been previously immunized, preformed circulating antibodies locally fixate complement at the injection site due to the high load of tetanus toxoid in the booster. This results in a local inflammatory vasculitis with pain, edema and skin ulceration. Accumulation of mononuclear cells occurs in cell-mediated (type IV) hypersensitivity. Langerhans cells are dendritic cells of the skin that present foreign antigens in response to infection or foreign bodies, but antigen capture in the epidermis has no role in the Arthus reaction. Histamine release is a key component of immediate (type I) hypersensitivity. IgM and IgG proliferation occur in antibody-mediated (type II) hypersensitivity reactions.
75. A is the correct answer.
Inflammatory carcinoma of the breast creates pitting classically referred to as an "orange peel" appearance on clinical exam. It produces a rapid increase in breast size, itching, redness and warmth of the overlying skin. There is usually no obvious lump, and likewise inflammatory carcinoma is often confused with mastitis on clinical exam. The pitting is caused by severe inflammation destroying the suspensory (Cooper's) ligaments attaching breast tissue to the dermis, resulting in a dimpled "orange peel." The remaining answers do not play a part in the pathogenesis of pitting in inflammatory carcinoma.
76. F is the correct answer.
You need to know the likely organisms that cause osteomyelitis, and determine which of these are associated with sickle cell disease. In general, Staph aureus and Salmonella enteritidis are the two most common causes of osteomyelitis in general. The vaso-occlusive bone disease related to sickle cell leaves the bone prone to infection. Here, the best answer choice is (F) Salmonella enteritidis. (A) Clostridium family bugs cause Gas Gangrene, myonecrosis and septicemia, NOT osteomyelitis. (B) Enterococcus faecalis is a Gram-Positive bacterium that normally inhabits the human gastrointestinal tract. It can exhibit antibiotic resistance and cause endocarditis and bladder or prostate infections. (C) Listeria monocytogenes is a Gram positive, motile (with flagella) organism. It causes the disease Listerosis, which is characterized by septicemia, encephalitis and uterine/cervical infections. (D) Proteus mirabilis is a Gram-negative, facultatively anaerobic bacterium. It shows swarming, motility, and urease activity. So, Proteus infection commonly results in struvite or calcium carbonate crystals in the urine, and to the formation of kidney stones.
77. E is the correct answer.
This question tests basic anatomical knowledge of the nerves and muscles of the hand and their functions. Such questions are rare on the actual USMLE, but do exist. The structure between the two tendons mentioned is the median nerve. Loss of the median nerve at the wrist results in loss of thenar muscle innervation, resulting in an inability to oppose the thumb. (A) Adduction and abduction of the fingers are mediated by the palmar and dorsal interosseus muscles of the hand, respectively. These are mostly innervated by the ulnar nerve. (B) Extension of the index finger requires forearm extensors. (C) Flexion of fingers 4 and 5 requires forearm flexor muscles. This is a wrist injury. (D) The ulnar nerve would mediate sensation over the base of the small finger. (E) Opposition of the thumb and other fingers involves flexion of the flexor carpi radialis (FCR) and flexor digitorum superficialis (FDS), both innervated my the median nerve. The FDS muscle in the forearm gives rise to 4 tendons that pass through the flexor retinaculum of the carpal tunnel and insert at the proximal interphalangeal joints. (So, it's an extrinsic muscle of the hand.) The FCR muscle passes a tendon just lateral to the FC-ulnaris tendon, and inserts at the base of the 2nd metacarpal.
78. D is the correct answer.
This question tests knowledge of the changes in fuel metabolism that occur with starvation. Skeletal muscle oxidizes fuels to produce Acetyl CoA, which enters the citric acid cycle to yield ATP for energy during use. We need only to know which fuel provides the Acetyl CoA after 2 days of starvation. Let's go step by step. In the resting state, skeletal muscles degrade adipose tissue triglycerides (C) and ketone bodies from the liver. During heavy bursts of activity, muscle uses phosphocreatine (A) stores and anaerobic respiration to break down muscle glycogen (B) to lactic acid. Moderately active muscle uses blood glucose (E) in addition to adipose-fatty acids and ketone bodies. After an overnight fast, glycogen stores in the liver and muscle become depleted. After 24 hours, the blood glucose concentration begins to fall and glucagon is released. After prolonged starvation (>24 hours), skeletal muscle uses circulating fatty acids (D) from triacylglycerol molecules that were broken down in adipose tissue. This permits the efficient use of fuel for muscle while reserving glucose (and later ketones) for the brain.
79. B is the correct answer.
Increased urinary excretion of catecholamines suggests increased production of catecholamines, a process that occurs in the adrenal medulla. (You should know the various layers of the adrenal glands and the respective hormones produced in each layer.) The patient presents with symptoms of hypertension secondary to a suprarenal mass, consistent with a pheochromocytoma. You should know that such masses are much more commonly benign (only 10% malignant). Therefore (B) benign neoplasm of the adrenal medulla is the most likely cause.
80. H is the correct answer.
The key to answering this question is focussing on 4 key points: 1. diarrhea with or without blood 2. location: inflammatory changes are seen in the DISTAL part of the colon only 3. number of lesions: there are multiple ulcerations 4. depth of lesion: these ulcerations are limited to the mucosa. Ulcerative colitis matches the characterization in the question stem along these 4 four points. The various diseases listed in the answer choices can best be differentiated based on the 4 points listed above. In particular, you must be familiar with the differences between Crohn's disease (B) and Ulcerative Colitis (E). (A) AIDS associated gastroenteritis results in pathological changes more proximally than described here, and would not selectively target the colon. Futher, AIDS complications rarely result in inflammatory changes. (B) Crohn's disease may occur anywhere throughout the colon and occurs in a patchy, discontinuous fashion. It penetrates deeper into the mucosa producing transmural fistulae and inflammation, unlike UC. (C) C.difficile colitis (also called pseudomembranous colitis) typically affects older patients who have had prior exposure to antibiotics and rarely produces bloody diarrhea. (D) E. coli is the most common cause of bacterial colitis, and depending on the pathogenic strain, may present differently. Notably, the lamina propria of the large intestine is infiltrated by polymorphonuclear leukocytes, without producing such a pattern of mucosal inflammation.
81. D is the correct answer.
This girl has severe carditis, which resulting enlargement of the cardiac shadow and acute congestive heart failure. This is a severe consequence of rheumatic fever, which is suggested by the acute-onset polyarthritis and rash (erythema marginatum). Rheumatic fever generally occurs 1-5 weeks after an upper respiratory infection caused by beta-hemolytic streptococcus. It is postulated that the immune system's response to the strep results in attack also on native tissues with similar antigens ("molecular mimicry"). Averting the possibility of rheumatic fever after streptococcus infection is the basis of penicillin treatment and prophylaxis for all people with suspected infection.
82. C is the correct answer.
All the described abnormalities point to Cri-du-Chat syndrome, uniquely characterized by a 'crying of the cat' like vocalization made by affected infants. Cri-du-chat results from deletion of part of the short arm of chromosome 5, and spares the normal diploid number. This answer choice is 46,XX,del(5)(p12). 46,XX,del(5)(p12) describes a rare translocation that results in Acute Lymphoblastic Leukemia, not developmental disorders. 46,XX,del(5)(p12) indicates a trisomy in Chromosome 13, resulting in severe mental retardation and growth abnormalities called Patau's Syndrome. The description above suggests that this is not the best answer. 47,XX,+21 describes Trisomy in chr 21, which is classically Down's Syndrome. While Down's syndrome may result in microcephaly, it would most prominently cause mental retardation. 69,XXY is a total triploidy and usually incompatible with life.
83. D is the correct answer.
The sudden onset of edema in the face and dependent limbs, coupled with hypoalbuminemia suggests a nephrotic syndrome in this child. Consistently, she has hyperlipidemia (cholesterol >200mg) and proteinuria. In children, the most common cause of a nephrotic syndrome is Minimal Change Disease (D, abbrev. MCD). The child does not exhibit hypertension or overt hematuria. This eliminates renal diseases that are associated with a more NEPHRITIC picture, such as membranoproliferative glomerulonephritis (C) and Rapidly Progressive GN (E). Be sure to review NEPHROTIC vs NEPHRITIC syndromes. MCD, (aka lipoid nephrosis) involves T cell mediated destruction of the polyanion charge barrier on epithelial foot processes, which results in leakage of albumin into the urine. This is manifest in this patient as a reduced serum Albumin (<3.5mg) and Protenuria (>0.15g/24h). While MCD is often idiopathic, it has been described to occur days to weeks after upper respiratory infections, as here. It is difficult to differentiate between MCD and the other nephrotic choices clinically, but you should know these important distinctions in their histology: By definition, patients with MCD present histologically with normal looking glomeruli. Focal segmental Glomerulosclerosis (A, FSGS) presents with focal sclerotic plaques of the glomerular tufts and hyaline deposits. It is also often associated with HIV and IV drug use. Membranous glomerulonephritis (B) presents later in life, insidiously and is an immune complex disorder that results in mesangial deposits. The workup will show positive Anti nuclear antibodies and/or Anti dsDNA. (remember, this is a NEPHROPATHY and is assoc. with a NEPHROTIC picture despite its name).
84. A is the correct answer.
To answer this question, you must know which organelles are sources of calcium available for use WITHIN the cell. The main sources of calcium in eukaryotic cells are the Smooth Endoplasmic Reticulum (A, SER) and the mitochondria (C). Release of intracellular calcium stores upon G protein activation follows a well established pathway: the beta-gamma subunit of a G-protein is cleaved and proceeds to activate Phospholipase C (PLC). PLC, in turn, cleaves the membrane bound phospholipid [phosphatidylinositol 4,5-bisphosphate] (PIP2) molecule into 2 components: Diacylglycerol (DAG) and Inositoltriphosphate (IP3). IP3 then binds to IP3 receptors present on the surface of the SER, which opens calcium channels and releases Ca2++ into the cytosol. Calcium release by the mitochondria is not the direct target of the G-protein mediated calcium release. The other answer choices are mere distractors and are NOT sources of calcium within animal cells.
85. B is the correct answer.
This girl has suffered from intussusception (choice B), when a piece of bowel gets “telescoped” into the proximal bowel, leading to ischemia and infarction. The patient’s abdominal pain and vomiting are consistent with this diagnosis. The picture is key to this question, since all of the other choices could have similar clinical presentations. Appendicitis (choice A) would also present with RLQ pain and vomiting but would not involve the adjacent bowel. Meckel diverticulum (choice C) would present similarly to appendicitis but the would show an outpouching of bowel, not an entire infarcted region. Necrotizing enterocolitis (choice D) is unusual in a four year old; most patients are newborns. Strangulated hernia (choice E), would present similarly but the pathology would not show one piece of bowel telescoped into the other.
86. D is the correct answer.
The question stem provides 3 useful hints which all point to Neutrophils (D) as the answer. First, the boy's infections are of pyogenic origin, indicating bacterial infection that results in pus formation. Pus consists primarily of expended neutrophils. Since there is a defect in the pyogenic response (resulting in repeated infection), there is most likely a defect in the action of Neutrophils. Second, his normal antibody response to immunizations can help you rule out B Lymphocytes (A) or Macrophages (C, the most common antigen presenting cell type) as the answers. Third, a normal recovery from chickenpox and measles (both viruses) requires intact function of T lymphocytes (E) and Eosinophils (B, because they contain abundant RNAses). The other answers do not play a direct role in the body's response to pyogenic infections.
87. C is the correct answer.
Normal grief reaction, an emotional response to loss lasting up to 6 months, is characterized by feelings of physical pain, distress, and physical and emotional suffering. It may include symptoms such as diminished appetite, difficulty sleeping, restlessness, anhedonia, auditory and visual hallucinations, and feelings of guilt. Although patients suffering from a normal grief reaction may be depressed, the diagnosis of major depressive disorder is reserved for a small subset with generalized feelings of hopelessness, helplessness, worthlessness, and guilt that persists for more than 6 months. Dysthymic disorder has some features of major depressive disorder (anhedonia, sleep disturbance, etc.) but usually does not last as long and is not as disabling. Obsessive-compulsive disorder is a mood disorder that involves distressing, intrusive thoughts (obsessions), and the ritualized repetitive behaviors (compulsions) sometimes employed to ward them off. Schizoaffective disorder comprises features of both schizophrenia and a mood disorder, and may include delusions, disorganized thinking and/or speech, and manic and/or depressive episodes.
88. A is the correct answer.
Presbycusis, or age-related sensorineural hearing loss, affects a majority of the elderly. Hearing loss is usually symmetrical, and is most prominent in high-frequency tones. Diminished perception of any of the other tones in the list suggests a pathological condition and warrants further work-up.
89. B is the correct answer.
Increased carbon dioxide shifts the oxygen-dissociation curve to the right, leading to an increase in oxygen unloading. Curve B is the only option that depicts this right-shift while maintaining the shape of the curve. Other factors you should know that can shift the curve to the right include higher temperature, increased 2,3-BPG, and lower pH.
90. C is the correct answer.
This patient may be developing rhabdomyolysis - a very serious complication involving muscle necrosis and release of cellular contents into the bloodstream. Clinical signs include diffuse muscle pain, increased serum creatine kinase, elevated serum potassium, and acute renal failure - indicated by a rapidly rising creatinine level. Although rhabdomyolysis is a rare side effect, it has been associated with the administration of statins, such as lovastatin, especially when taken in combination with cyclosporine or fibrates. None of the other drugs listed above has been associated with rhabdomyolysis.
91. D is the correct answer.
This patient has been poisoned by the organophosphate parathion. Organophosphates inhibit acetylcholinesterase (AChE), leading to toxic build-up of acetylcholine (ACh) and resulting in the symptoms listed above. Remember the mnemonic DUMBELS associated with cholinergic toxicity: Defecatioin, Urination, Miosis, Bronchorrhea/Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation.
92. C is the correct answer.
To answer this question, you need to know that pain and temperature sensation are carried in the spinothalamic tract. Therefore, impaired pain and temperature sensation points to a lesion in the contralateral spinothalamic tract (Region C). Specifically, the spinothalamic tract carries information about pain and temperature from the contralateral side of the body from the dorsal root ganglion, crossing at the anterior white commissure and finally synapsing in the VPL thalamic nucleus. Region A is the hypoglossal nerve (cranial nerve XII), which controls the tongue muscles. Region B is the trigeminal nerve (cranial nerve V) which carries pain and temperature from the ipsilateral face. Region D shows damage to the medullary pyramid which controls the skeletal muscles of the contralateral body. Region E is the medial lemniscus, which controls proprioception and fine touch of the contralateral body.
93. A is the correct answer.
Small, atretic ovarian follicles are a normal finding in post-menopausal women. As women enter menopause, their ovaries lose the ability to support viable ova and follicles. This process of planned cell death is called apoptosis. By contrast, necrosis is unplanned cell death caused by an insult to previously viable tissue. Metaplasia and transformation are associated with neoplastic processes, which may be occurring in this woman's uterus leading to bleeding. Don't be fooled, the question asks not about uterine histological findings, but rather about those in the ovaries which are entirely benign.
94. D is the correct answer.
95. B is the correct answer.
A high spiking fever and shaking chills after a trip to central Africa is a classical story for malaria of the Plasmodium genus. The conventional method for diagnosing malaria is a (B) Giemsa-stained blood smear. (A) Acid-fast stains are classically used for diagnosis of tuberculosis, while (D) India ink wet mount is known for its use with Cryptococcus neoformans. (E) KOH stain is used for fungal elements in thick mucoid material and in specimens containing keratinous material, such as skin scales, nails, or hair.
96. A is the correct answer.
The commonly-used HIV medications have well-known side effects. In particular, zidovudine (AZT), the commonly-used nucleoside reverse transcriptase inhibitor (NRTI), may cause anemia through (A) decreased formation of erythrocytes. Approximately 1% of patients experience this adverse effect after 2-4 weeks of taking the medication. Other significant side effects of AZT are headache (63%), malaise (53%), nausea (51%), anorexia (20%), vomiting (17%), constipation (6%), and granulocytopenia (2%), anemia (1%). (B) Folic acid deficiency and (E) iron deficiency may, respectively, cause macrocytic and microcytic anemia, but they are not in and of themselves related to HIV medications. Similarly, these medications do not affect (C) the formation of erythrocyte antibodies or (D) the fragility of erythrocytes.
97. E is the correct answer.
In this patient with a history of ovarian cancer, the most likely cause of her edema is (E) obstruction of lymph vessels secondary to her malignancy. While various clinical conditions can cause edema, including congestive heart failure, cirrhosis, and nephrotic syndrome, these disorders are typically associated with pitting edema. This patient presents with nonpitting lymphedema, characterized by its involvement of an isolated limb. (A) Decreased capillary hydrostatic pressure would not cause edema, although increased capillary hydrostatic pressure would. (B) Decreased interstitial hydrostatic pressure is unlikely. (C) Increased capillary oncotic pressure would not cause edema, although decreased capillary oncotic pressure would. (D) Increased capillary permeability, as in seen in burns, trauma, inflammation, sepsis, and allergic reactions, may cause edema. However, this presentation makes lymphedema much more likely.
98. E is the correct answer.
Rhabdomyolysis (Choice E) occurs when muscle fibers break down, often due to stress (such as running a race), releasing myoglobin into the bloodstream, which can then damage the kidneys. The recent history of a race, as well as the urinalysis which is positive for blood on dipstick but negative for RBCs supports this diagnosis. Acute glomerulonephritis (Choice A) usually results in red blood cells in the urine and is unlikely with no history of infection or other symptoms. Hypovolemia (Choice B) can lead to acute renal failure by prerenal mechanism but would not cause a positive dipstick for blood. Renal infarct (Choice C) would present with severe pain and renal failure, as would renal vein thrombosis (Choice D).
99. F is the correct answer.
To answer this question, you need to know that beta-thalassemia major is caused by under-production of the beta globin protein, the product of the beta-globin gene. Since all three of the nucleotides in this question are upstream of the transcription start site, they are not part of the gene transcribed, and therefore are not required for binding elongation factors, such as eIF4F (choice A) or eIF4G (choice B), which are involved in translation of proteins, not the transcription. Similarly, histone acetylase and deacetylase (choices C and D) are involved in chromatin packing of the gene as a whole, not a particular region, as in this example. A loss of function mutation in positive-acting transcription factors (choice F) is the only choice that would result in under-production of the entire protein product by affecting the promotor region.
99. A is the correct answer.
Doxorubicin has a well known side-effect profile of (A) dilated cardiomyopathy, with dose-related CHF and transient ECG abnormalities occuring in over 10% of patients. Other side effects include leukopenia (75%) nausea and vomiting (21-55%). It is not as closely associated with restrictive cardiomyopathy or pulmonary disease. The chemotherapeutic agent bleomycin is better known for causing pulmonary toxicity, particularly pulmonary fibrosis.
99. A is the correct answer.
A warm, painful, and erythematous breast mass (often accompanied by fluctuance), experienced by breast-feeding women, that resolves with antibiotics suggests an infectious cause. Although far less common than mastitis, a breast abscess is the only infectious etiology among the answer choices. Risk factors include primiparity, maternal age >30, and a pregnancy lasting longer than 41 weeks. Fibrosis (scarring) can replace the abscess in some women, leaving a firm mass and dimpled overlying skin months after the abscess has resolved.
100. B is the correct answer.
This man is exhibiting the classic signs of (B) delirium: an acute change in mental status, inattention, disorganized thinking, and a fluctuating level of awareness. Delirium can be caused by any of the following in the mnemonic P. DIMM WIT: Postoperative state, Dehydration/malnutrition, Infection, Medications, Metals (heavy metals exposure), Withdrawal from alcohol/drugs, Inflammation, and, as in this case, Trauma/Burns. The acute onset of this change in mental status makes (B) delirium a much more likely diagnosis than (A) adjustment disorder, (C) Paranoid personality disorder, (D) Schizophrenia, or (E) Alzheimer's dementia.
100. B is the correct answer.
Severe combined (T and B) immunodeficiency, also known as SCID, is caused a purine salvage pathway deficiency of (B) adenosine deaminase. Without this enzyme to convert adenosine to inosine, there is an excess of ATP, dATP, and S-adenosylhomocysteine. These substances are toxic to immature lymphoid cells, and also prevent DNA synthesis through feedback inhibition of ribonucleotide reductase. Therefore, lymphoid cells fail either to reach maturity or to be produced in the first place, resulting in SCID. Deficiency of (A) adenine phosphoriboxyltransferase (APRT) may lead to kidney stones formed of adenine and salts. Deficiency of (C) adenosine kinase is associated with nonspecific developmental abnormalities. (D) Adenylosuccinate synthetase deficiency has been implicated in the development of hyperuricemia and gout. Deficiency of (E) Hypoxanthine-guanine phosphoribosyltransferase causes Lesch-Nyhan Syndrome, characterized by self-mutilation, retardation, aggression, hyperuricemia, and gout.
101. D is the correct answer.
Immune thrombocytopenic purpura (ITP) (D) causes a profound decrease in platelets, can reveal petechiae on physical exam, and should be of rapid onset with all other laboratory values normal. Bone marrow biopsy would reveal normal-to-increased numbers of megakaryocytes. Marrow biopsy in acute megakaryocytic leukemia (A) would show hypercellular marrow replaced by blast cells and dysmorphic promegakaryocytes and megakaryocytes. This patient has mature megakaryocytes. In acute myelogenous leukemia (B), blast red cells should be seen in the peripheral smear and bone marrow. This patient has normal red cell morphology. In aplastic anemia (C) there are profound decreases in red cells, white cells, and platelets. This patient has normal RBC and WBC values. Epstein-Barr (EBV) viral infection (E) is usually associated with a leukocytosis and mild thrombocytopenia, not the normal WBC count and profound platelet deficiency seen here. Though immune thrombocytopenic purpura is a rare complication of EBV, (D) is a better answer choice in this situation.
102. B is the correct answer.
Acute physical or psychological stress activates the hypothalamic-pituitary-adrenal axis, resulting in increased plasma ACTH and (B) cortisol concentrations. Fever, caused by systemic infection or by pyrogen administration, is a potent stimulus of ACTH and cortisol secretion, while infection causes release of interleukins IL-1 and IL-6, which stimulate hypothalamic CRH secretion, and tumor necrosis factor-alpha, which stimulates ACTH secretion directly. Cortisol, in turn, acts as a physiological antagonist to insulin by inhibiting glycogenesis, promoting lipolysis, and mobilizing extrahepatic amino acids and ketone bodies. This leads to gluconeogenesis with resultant increased circulating glucose concentrations.
103. D is the correct answer.
Quadrant D (D) contains CD4+ T lymphocytes (a.k.a “helper” T cells). This population is activated by antigen presented on major histocompatibility complex (MHC) class II molecules, which are only expressed on “professional” antigen presenting cells (APCs). These antigens are fragments of nonself peptides internalized by APCs. This CD4+ population would respond to hepatitis A virus vaccine. Quadrant A (A) contains CD8+ T lymphocytes (a.k.a. “cytotoxic” T cells). This population is activated by antigen presented on major histocompatibility complex (MHC) class I molecules, which are expressed on nearly all nucleated cells. Such antigens are selected at random from cytosol content, and may be self- or nonself-peptides (e.g. infectious virion). This CD8+ population would respond to virulent hepatitis A virus, but not the vaccine. Quadrant B (B) contains CD4+ CD8+ T lymphocytes, corresponding to an intrathymic (immature) phenotype. Such cells are usually not seen peripherally, and do not express mature T cell function. Quadrant C (C) would contain CD4- CD8- T lymphocytes. Such cells would be abnormal and would not be involved in a vaccine response.
104. E is the correct answer.
A connexon is an assembly of 6 proteins (called connexins) that forms a gap junction in the (E) transmembrane region between the cytoplasm of two adjacent cells. The connexon is actually the hemichannel supplied by a cell on one side of the junction; two connexons from opposing cells normally come together to form the complete intercellular gap junction channel. However, in some cells, the hemichannel itself is active as a conduit between the cytoplasm and the extracellular space.
106. B is the correct answer.
Prolonged bleeding times are commonly seen in infants who have a deficiency of Vitamin K. The sterile intestines of newborns are lacking in intestinal flora to synthesize Vitamin K, and this newborn is at particular risk, having recently undergone an antibiotic regimen. Therefore, she is likely deficient in Vitamin K. Vitamin K is necessary for the (B) γ (gamma) carboxylation of glutamic acid residues of proteins necessary for blood clotting. Vitamin K-dependent clotting factors II, VII, IX, and X are therefore deficient, resulting in prolonged PT and aPTT times. Anticoagulant Proteins C and S are also affected by the lack of Vitamin K, but the hypocoagulability is more significant in Vitamin K deficiency.
107. E is the correct answer.
Proteinuria, edema, and hypertension after 20 weeks' gestation in a previously normotensive woman are pathognomonic for (E) preeclampsia. Preeclampsia occurs in approximately 5 to 8 percent in the United States, although it is mild in 75 percent of cases. This disease is associated with the HELLP syndrome (Hemolysis, Elevated LFTs, Low Platelets.) When the above presentation includes seizures, a diagnosis of (C) eclampsia is made. In this case, this woman's headaches are caused by hypertension, while her edema is secondary to the reduced plasma oncotic pressure following protein loss in the urine. (A) Acute glomerulonephritis can cause hypertension, but is less likely to cause edema, while (D) Nephrotic syndrome causes edema without hypertension. (B) Congestive heart failure does not cause orbital edema.
108. B is the correct answer.
The lab values for hemotocrit and hemoglobin indicate that this women has anemia. Her MCV value of 70 is consistent with a microcytic anemia. The most common microcytic anemia is iron deficiency anemia. Chronic blood loss through the GI tract is the most common cause of iron deficiency anemia in men and post menopausal women. An acquired hemolytic anemia likely would present with additional symptoms on physical exam, including signs of jaundice, dark urine upon standing, and splenomegaly. Also, the history does not suggest a cause for hemolysis. Beta-Thalassmia minor is a mild microcytic anemia. In the majority of cases, Beta-Thalassemia minor is asymptomatic, and many affected people are unaware of the disorder. This is an inherited anemia that would not present late in life with increasing shortness of breath. Folic acid deficiency and Pernicious anemia leading to Vitamin B12 deficiency are both types of macrocytic and megaloblastic anemia. The MCV value would be elevated above 96 micrometer^3 and these types of anemia are less common than iron deficiency anemia.
109. A is the correct answer.
COPD describes patients with chronic bronchitis and/or emphysema who have a decreased forced expiratory volume. The overwhelming majority of patients with chronic bronchitis are smokers, up to 90% of all cases. Cigarette smoking also has been shown to be the major cause of emphysema. Therefore, decreasing the prevalence of cigarette smoking would lead to the greatest decrease in COPD in the community. Persons with COPD are advised to get the flu and pneumococcal immunizations to help prevent serious infections in patients with compromised lung function. Patients with COPD have increased frequency and severity of lung infections and this likely plays a role in the etiology and progression of COPD, but not nearly to the extent of cigarette smoking. Therefore, increasing the rate of flu and pneumococcal immunizations would not lead to the greatest decrease of COPD. Similarly, decreasing radon levels may decrease the prevalence of COPD, but only to a smaller extent when compared with cigarette smoking. Increasing exercise will not decrease COPD in this community, especially if they continue to smoke cigarettes.
110. C is the correct answer.
A noncompetitive antagonist (C) binds at a different site than the receptor, or irreversibly binds the receptor site. In either case, the system is not activated. Thus, response is lowered at a given dose of agonist, and this effect is not overcome with increased agonist dose. (The dose-response curve shifts downward.) Drug W meets this description. A competitive antagonist (A) reversibly binds to a receptor without activating the system, lowering the response at a given agonist dose. However, a response of maximum efficacy may be achieved with increased agonist dose. (The dose-response curve shifts to the right.) Drug W is not a competitive antagonist because it acts at a site other than the receptor for drug V. Further, it is not stated that the effect of drug W is overcome with increasing doses of drug V. A full agonist (B) will produce a response of maximum efficacy if present in sufficient quantity. Drug W cannot be a full agonist, because it diminishes the physiologic effect of drug V. When administered alone, a partial agonist (D) binds to the receptor site and elicits a less-than-100% response regardless of dose. When administered with a full agonist, it acts like an antagonist because it competes for receptor binding sites. (The dose-response curve shifts downward, and may also shift left or right.) Drug W cannot be a partial agonist because it acts at a site other than the receptor for drug V. A reverse agonist (or inverse agonist) (E) binds to the same receptor site as an agonist, but elicits the opposite effect. This choice is incorrect because drug W does not bind at the same site as drug V, and only a diminished (rather than opposite) effect is observed.
111. B is the correct answer.
During the cephalic and gastric phases that occur after the child eats breakfast, secretions from the pancreas have high concentrations of digestive enzymes in the form of inactive precursors, including trypsinogen. The increased amount of trypsinogen in the duodenum is a result of stimulation of acinar cells by vagal input during cephalic phase and vago-vagal reflex secondary to stomach distention. Degradation of trypsin does not lead to increased trypsinogen within the duodenum. The rate of trypsinogen activation does not increase the amount of trypsinogen in the duodenum. It only increases the amount of activated trypsinogen or trypsin in the duodenum. Therefore, the actual amount of trypsinogen in the duodenum decreases as the trypsinogen is activated to trypsin. Transcription of the trypsinogen gene and translation of the trypsinogen mRNA occur within the acinar cells of the exocrine pancreas and these processes increase the amount of trypsinogen within the acinar cells. However, it is the action of the vagus nerve to increase exocytosis of trypsinogen that leads to an increase of trypsinogen within the duodenum.
112. C is the correct answer.
Thyroid peroxidase is the enzyme responsible for iodide oxidation and binding to tyrosine in the follicle lumen. The other steps in thyroid synthesis including cleavage of iodine from iodinated tyrosines, endocytosis of colloid, movement of iodide from plasma into thyroid cells, and separation of thyroxine from thyroglobulin in lysosomes, do not require thyroid peroxidase and would therefore not be inhibited in the transgenic animal.
113. B is the correct answer.
The woman experienced a panic attack, which can mimic heart attacks. After the resolution of a panic attack, the medical evaluation would be normal, which distinguishes these attacks from multiple heart attacks. The most appropriate nonpharmacologic therapy is cognitive behavioral therapy. The goal of this therapy is to change the way a patient interprets the world in order to change the patient's response to problems. For patients who experience panic attacks, cognitive behavioral therapy can help them to increase adaptive behavior and decrease emotional distress, thereby decreasing the amount of panic attacks. Assertiveness training is a subtype of cognitive behavioral therapy. However, it is not the most appropriate therapy since it only address one aspect of the woman's disorder. Assertiveness training may help decrease social anxiety, but if that is not the only trigger for this woman's panic attacks, then it would not be sufficient for therapy. Dynamic psychotherapy is a form of talking and relational therapy that is best used for adjustment, personality, depressive, and eating disorders. It also takes several months to years for the therapy to be effective. Therefore, it would not be appropriate for helping the woman with her recurrent panic attacks. Psychoanalysis is a specific type of treatment where the analyst, upon hearing the thoughts of the patient, formulates and then explains the unconscious basis for the patient's symptoms and character problems. It can be used for panic attacks and anxiety disorders, but it would not be the most appropriate therapy since this woman would benefit more from relaxation training and systemic desensitization that are associated with cognitive behavioral therapy. Psychodrama is a kind of group therapy in which group members act out their problems in a way to better understand conflicts between people. This type of therapy would not be appropriate for the woman and may even provoke another panic attack.
114. E is the correct answer.
The 9-month-old girl likely has phenylketonuria (PKU). In this disorder, there is a deficiency of phenylalanine hydroxylase or tetrahydrobiopterin cofactor, which causes a buildup of phenylalanine. State-mandated newborn screening looks for evidence of PKU to prevent the complications and developmental delays that occur in PKU when phenylalanine builds up in the body. The excess phenylalanine spills over into the urine as phenylacetic acid. The musty odor is a clue to the diagnosis. Since this is a disorder of aromatic amino acid metabolism, there is a musty odor in the diapers. Other common findings in PKU include fair skin, mental retardation, and growth retardation. There would be an increased concentration of homocysteine in the urine in homocysteinuria, which is caused by cystathionine synthase deficiency, decreased affinity of cystathionine synthase for pyridoxal phosphate, or methionine synthase deficiency. Common findings with this disease include mental retardation, osteoporosis, tall statue, kyphosis, lens subluxation, and atherosclerosis. Increased isoleucine in the urine likely result from blocked degradation of branched amino acids due to a lack of alpha-ketoacid dehydrogenase deficiency. This disease is maple syrup urine disease and the urine ofen smells like maple syrup. Homogentisic acid in the urine is seen in alkaptonuria. In this disease, there is a deficiency of homogentisic acid oxidase. The common finding in this disease is that urine turns dark on standing and connective tissue may be darker in color. Increased concentration of isovaleric acid in the urine can be found in isovaleric acidemia. Patients with isovaleric acidemia may present in early neonatal life with a sudden onset and severe illness. The illness usually begins within a few days of birth with increasing lethargy and decreased feeding, which often causes dehydration and weight loss. The classic odor in this disease is an "odor of sweaty feet" that represents the accumulation in the body of isovaleric acid and related compounds.
115. H is the correct answer.
A 10-month-old child that can sit unassisted and has started to crawl has normal motor function. Infants do not start to walk until about 15 months. Her social and cognitive development are also normal. It is normal for infants to babble at 10 months and to be able to speak a few words by 15 months. Finally, the separation anxiety is also normal for infants between the ages of 10-15 months old. If this 10-month-old girl was not able to sit unassisted, crawl, and babble, then her motor and cognitive development would be described as delayed because these are important milestones that occur in infants between 7-9 months. In addition, the presence of separation anxiety is normal for her age and up to 15-months-old and therefore is not a sign of delayed social development.
116. A is the correct answer.
Tinea corporis or ringworm is a fungal infection. An effective treatment for this infection is a topical azole that acts by blocking ergosterol synthesis and thereby increasing fungal membrane permeability. Miconazole and clotimazole are two azoles available in topical solutions that can be used to treat this infection. Inhibition of DNA synthesis is the mechanism of action of flucytosine, which converts to fluorouracil and competes with uracil. This drug can be used to treat systemic fungal infections, but the side effects of nausea, vomiting, diarrhea, and bone marrow suppression limit its use. Inhibition of ribosomal protein synthesis is the mechanism of action of various antibacterial agents including aminoglycosides, tetracyclines, chloramphenicol, erythromycin, Lincomycin, and Clindamycin. These drugs are used to treat various bacterial infections, but they are not used to treat fungal infections. Interference with mycolic acid synthesis is how Isoniazid works. Isoniazid is a drug used for tuberculosis prophylaxis and in combination with other drugs for therapy for active tuberculosis. Isoniazid is not used to treat fungal infections. Rifampin is another drug used in combination with Isoniazid for active tuberculosis therapy. It works by irreversibly binding to and inhibition of DNA-dependent RNA polymerase. Rifampin also is used for meningococcal prophylaxis, but it is not used to treat fungal infections.
117. E is the correct answer.
The midsystolic murmur heard best in the left third intercostal space associated with a thrill is consistent with the murmur of a ventricular septal defect (VSD). Of the answer choices above, only Tetralogy of Fallot includes a VSD. In addition to a VSD, patients with Tetralogy of Fallot also have pulmonary stenosis, right ventricular hypertrophy, and overriding aorta. These patients often present shortly after birth with cyanosis. An atrial septal defect would present with a loud S1 and a wide, fixed split S2 on physical exam and it is unlikely that the patient would present with cyanosis. The bicuspid aortic valve would not present with cyanosis. Many patients live with unrecognized bicuspid aortic valves until later in life with the development of aortic stenosis secondary to calcifications of the valve leaflets. Patent ductus arteriosus likely would present with a continuous machine-like murmur. Coarctation of the aorta is associated with elevated blood pressure in the upper extremities and decreased blood pressure in the lower extremities. If these patients present shortly after birth, they often have cyanosis of the lower extremity only.
118. D is the correct answer.
Visual accommodation occurs by contraction of the ciliary muscle to increase the curvature of the lens. Parasympathetic nerve fibers are responsible for ciliary muscle contraction and these act on muscarinic receptors. The muscarinic receptors are activated by acetylcholine to stimulate contraction of the ciliary body. Many antidepressant drugs have anti-cholinergic properties, thus blocking the muscarinic receptors and resulting in the loss of visual accommodation. Antidepressant medication also may have anti-histaminergic and anti-serotoninergic properties. However, these two receptors are not found in the ciliary muscle and are not responsible for stimulating visual accommodation. There are no beta-adrenergic receptors that stimulate the ciliary muscle of the eye. Therefore, blockade of beta-adrenergic receptors would not cause loss of visual accommodation. There are alpha-adrenergic receptors located in the radial muscle of the eye, but this muscle is not responsible for visual accommodation.
119. C is the correct answer.
Hepatotoxicity is a well known side effect of isoniazid. Pyridoxine is given with isoniazid to help prevent B6 deficiency and neurotoxicity. The proximity of this man's symptoms to starting isoniazid, normal chest x-ray, and lack of exposure make tuberculosis and hepatitis B unlikely. Cholecystitis is not a well-known toxicity of pyridoxine and jaundice is not a typical feature of cholecystitis.
120. B is the correct answer.
Colchicine is effective in acute gout. It inhibits polymerization of microtubules and leukocyte chemotaxis. (A) Allopurinol, (D) probenecid, and (E) sulfinpyrazone should be avoided during an acute flair because rapid changes in serum uric acid concentrations can precipitate crystalization of uric acid. Allopurinol inhibits uric acid production by inhibiting xanthene oxidase and probenecid inhibits uric acid reabsorption in the kidney. Sulfinpyrazone's mechanism of action is similar to probenecid. (C) Morphine is a nonspecific treatment choice for gout. Colchicine is a better first choice.
121. E is the correct answer.
Activated plasminogen (plasmin) degrades fibrin to fibrin split products. (A) Heparin activates antithrombin III, which decreases the activity of IIa and Xa. (B) Aspirin inhibits cyclooxygenase and thereby prostaglandin production by platelets. (C) Factor II (prothrombin) is the inactive form of IIa (thrombin). (D) TPA action is not dependent on fibrinogen concentration.
122. D is the correct answer.
Figure D shows a plateau of blood flow as mean arterial pressure (MAP) increases. This illustrates the phenomenon of autoregulation, in which tissues alter pre- or post-capillary resistance to keep blood flow relatively constant in the face of changing MAP. (The curve appears similar to those seen in pH buffer systems.) Figure A shows a direct relationship between blood flow and MAP. This is an absence of autoregulation. Figure B shows an inverse relationship between blood flow and MAP. This is abnormal and is not an example of autoregulation. Figure C shows an increase in blood flow at a constant MAP. This is abnormal and is not an example of autoregulation. Figure E shows a plateau of blood flow as MAP increases, but high blood flow should be seen with high MAP, not low.
123. C is the correct answer.
Eukaryotic genes contain introns and exons. Exons contain the genetic information that is transcribed into RNA while introns are spliced out during processing. Prokaryotic genes do not contain introns. Both prokaryotic and eukaryotic cells contain (A) cell membranes, (B) DNA, (D) mRNA, and (E) ribosomes.
124. E is the correct answer.
This man likely had ventricular fibrillation secondary to ischemic heart disease given his age, history of angina and type 2 diabetes, and his sudden collapse and death. Ventricular fibrillation is the most common cause of sudden cardiac death in adults. (A) Cardiac tamponade, (C) necrosis of the myocardium, and (D) rupture of the papillary muscle would be uncommon causes of sudden cardiac death and would most likely each present with their associated symptoms. (B) Embolus to the right middle cerebral artery would produce a stroke and not sudden cardiac death.
125. E is the correct answer.
This woman's clinical and radiographic history is consistent with the diagnosis of sarcoidosis. Sarcoidosis is characterized by widespread noncaseating granulomas, elevated serum ACE levels, and is associated with, among other things, restrictive lung disease. (A) Pulmonary hemorrhage is unlikely. There is no history of hemoptysis or evidence of hemorrhage on chest x-ray. (B) Liquefactive necrosis is often associated with cellular destruction, often secondary acute infection. (C) There is no suggestion of bronchiectasis or dilation of the respiratory bronchioles on history or radiography. (D) Bacterial infection with abscess formation is unlikely given this woman's clinical history and radiographic findings.
126. B is the correct answer.
C5a is the major factor responsible for neutrophil chemotaxis. Activation of both the classical and alternative complement pathways results in C5a production and eventual membrane attack complex (MAC) formation.
127. B is the correct answer.
(B) In the adrenal gland, the zona glomerulosa produces mineralocorticoids, the zona fasciculata produces glucocorticoids, and the zona reticularis produces androgens. This patient's pituitary tumor was likely causing compression/destruction of ACTH-secreting cells as well as LH/FSH-secreting cells of the pituitary. This caused atrophy of the zona fasciculata and zona reticularis, respectively. The zona glomerulosa, which responds primarily to angiotensin II and serum potassium levels was spared. An acute stressor, such as this woman's surgery, will increase the body's need for cortisol and can lead to acute adrenal crisis in a case such as this. We are not given any information that would lead us to believe there was autoimmune destruction, denervation, or granulomatous disease. This woman's cortisol deficiency was likely a cause of the tumor in her pituitary rather than a primary adrenal deficiency.
128. D is the correct answer.
(D) The most likely answer is irritable bowel syndrome. Alternating periods of constipation/diarrhea associated with psychosocial stress is typical of IBS. Physical and laboratory studies are normal in IBS. (A) Gastroenteritis generally follows more of an acute timeline, does not wax and wane, constipation is not typically a component of the illness, and gastroenteritis implies that there may be nausea/vomiting from stomach involvement. (B) Generalized anxiety disorder involves chronic anxiety often with little to provoke the anxiety and may include physical symptoms, but alternating periods of diarrhea/constipation is not a common complaint. Additionally, patients with GAD will tend to complain of anxiety related to a variety of everyday problems. This woman's anxiety is related specifically to her GI complaint. (C) We are not given any information to lead us to a diagnosis of hypochondriasis. She has no history of multiple visits to the doctor or hospital with undiagnosed problems. (E) We are not given information that would lead us to a diagnosis of major depressive disorder. This woman's anxiety is related to her GI complaints.
129. D is the correct answer.
Typically, body NaCl level is constant: NaCl excretion equals NaCl intake. However, administration of mineralocorticoid will cause the body to reabsorb more NaCl. For each day, the difference between NaCl intake and NaCl excretion equals NaCl retention. On day 1 he retains 170 mmol NaCl; on day 2 he retains an additional 110 mmol NaCl; on day 3 he retains an additional 20 mmol NaCl. On day 4, NaCl excretion equals NaCl intake, showing he has reached a new steady-state. Thus, overall he has retained 170 + 110 + 20 = 300 mmol NaCl. With free access to water and usual caloric intake, the retained NaCl is equivalent to addition of isotonic fluid. Given that 150 mmol NaCl weighs 1 kg, 300 mmol NaCl therefore weighs 2 kg. This 70-kg man will weigh 72 kg (answer D) at the end of day 4.
130. A is the correct answer.
Sildenafil (Viagra) is a commonly-used medication for erectile dysfunction and increasingly pulmonary hypertension. The drug is a potent cGMP phosphodiesterase 5 (PDE5) inhibitor. Thus, it blocks PDE5, which increases cellular cGMP in the corpus cavernosum. The increased cGMP promotes smooth muscle relaxation and vasodilitation, facilitating an erection. A major side effect of sildenafil is that the above cascade can also occur in the general circulation at the level of the arteriole, thus causing systemic vasodilitation. This may result in dizziness and orthostatic hypotension. Such symptoms are especially worsened by nitrates such as nitroglycerin, which is contraindicated in patients taking sildenafil or other PDE5 inhibitors.
131. E is the correct answer.
Skin cancer comes in three major forms - squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and melanoma. This patient's presentation and histology suggest squamous cell carcinoma. In general, a lesion described as ulcerated or with heaped borders is cancerous until proven otherwise. The atypical and dysplastic keratinocytes indicate a squamous cell origin. Actinic keratosis is a thick, scaly lesion that a predecessor lesion to SCC. It would be fair to consider in this patient except that the clinical presentation describes a lesion that has progressed much further. Melanoma is a neoplasm of melanocytes. Melanoma should be associated with ABCDE - Asymmetry, irregular Borders, multiple Colors, Diameter greater than 5mm, and Evolution of a pre-existing nevus. Melanoma is more common in younger people. Mycosis fungoides is a presenation of cutaneous T-cell lymphoma; this patient's histology is not suggestive of such a rare diagnosis.
132. A is the correct answer.
Paternalism is when a physician places his/her values system as the primary values system to make decisions for the care of the patient instead of deferring to the patient's values or autonomous decisions. In this case, the wishes of the patient should be represented by the family members as there is no living will or advanced directives. Preserving fairness would involve ethical decisions about who should receive scarce resources; a classic example deals with who should have priority in receiving organ transplants. A good example of protecting patient autonomy is the process of informed consent before procedures or experiments. Rationing care acknowledges scarce health resources must be appropriated based on their cost-effectiveness, even though an individual patient's health options may be diminished. A good example of truth-telling would involve the disclosure to a patient of his/her prognosis.
133. D is the correct answer.
The test is attempting to measure the alveolar ventilation, or the amount of gas reaching the alveoli that is capable of gas exchange. The 20 micrometer particles are not arriving as they are too large to pass through the 10+ levels of conducting airways. One can reach this answer through elimination of the others: A - macrophage ingestion takes a long time, and would not affect a quick scan such as this. There is no evidence that nonuniform ingestion, if it exists, can explain the problem with this aerosol. B - If the particles adhered to the walls, the more distal parts of the lung would be less ventilated by the particles, which would exacerbate the problem with the aerosol. C - This would happen uniformly throughout the lung, which would not affect the measurement of alveolar ventilation. E - The mucociliary system is exceedingly slow - it is an "elevator." This alone cannot explain the difficulty with the aerosol.
134. C is the correct answer.
The boy's wound appears to be superficial - he "scraped" his foot which is now infected (likely by a Gram positive organism such as Strep A or Staph). The superficial lymphatic drainage of the lower extremity roughly follows the superficial vessels. In this case of the lateral foot, the lymphatics drain along the path of the small saphenous vein to the popliteal fossa.
135. E is the correct answer.
Vitamin C deficiency (scurvy) classically presents with ecchymoses, petechaie, and gingival swelling. Vitamin C is necessary for the production of collagen; its deficiency results in a tendency towards weakened tissues and bleeding. Beriberi is due to a deficiency of thiamine (B1). It may present as either "wet" (high-output heart failure and peripheral edema) or "dry" (mostly peripheral neuritis and paralysis). Either can also present with Wernicke's encephalopathy (ataxia, confusion, opthalmoplegia/nystagmus). Kwashiorkor is found in children, generally under age 4, who suffer from severe protein malnutrition. Symptoms include edema, red hair, muscle wasting, and eventual death. Pellagra is due to niacin (B3) deficiency and classically presents with the D's - dermatitis, dementia, and diarrhea. Rickets is due to a vitamin D deficiency. It classically presents with symptoms/signs of osteomalacia or "softening" of the long bones - bowed legs, "knocked knees," greenstick fractures, costochondral pain, and especially growth disorders.
136. E is the correct answer.
Logically, a vaccine needs to work by inducing memory cells. There are two types of memory cells - T and B. Memory B cells (a variant of plasma cells) can only be produced after signaling from activated T cells. Thus, the vaccine will need to lead to the activation of T cells. The carrier protein in the vaccine enables it to be taken up and processed by antigen-presenting cells (dendritic cells, B cells, macrophages). The peptides are presented on MHC type II, which contact and activate T-lymphocytes, starting the above immune cascade.
CALCULATING YOUR SCORE
The scores below were tabulated using our vast database of student test results. Of course, there are a number of underlying assumptions in our calculations that affect the accuracy of the prediction. Nevertheless, we feel comfortable that this predicted score will give you a crude assessment of where you stand and what's required to achieve your target score.
| # Correct | Score | # Correct | Score | # Correct | Score |
144 143 142 141 140 139 138 137 136 135 134 133 132 131 130 129 128 127 126 125 124 |
269 268 266 265 263 262 261 259 258 256 255 254 252 251 249 248 247 245 244 242 241 |
123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 |
240 238 237 235 234 232 231 230 228 227 225 224 223 221 220 218 217 216 214 213 211 |
102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 |
210 209 207 206 204 203 202 200 199 197 196 194 193 192 190 189 187 186 185 183 182 |
| Copyright © 2008 WikiTestPrep™ | Terms and Conditions | About Us | Donate | Frequently Asked Questions | Contact Us |