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Exam Section 1: Item 1 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment " Exam Section 1: Item 1 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 14-year-old boy is brought to the physician by his parents because of increasingly severe left knee pain during the past week. The pain is exacerbated by running or kneeling. He plays multiple sports and is currently in the middle of soccer season. There has been no recent trauma to the area or related sports injuries. Physical examination shows full range of motion of both lower extremities. There is a discrete area of swelling just below the left patella over the proximal portion of the tibia. Palpation of the area produces pain. Pain is also reproduced when he does a full squat. Examination of the right knee shows no abnormalities. Which of the following is the most likely cause of this patient's condition? A) Chondromalacia B) Ligamental tear C) Osgood-Schlatter disease D) Osteochondritis
E) St - CORRECT ANSWER C.
Osgood-Schlatter disease refers to osteochondrosis or traction apophysitis of the tibial tubercle that typically occurs in adolescent, athletic children. Repetitive tension via the patellar tendon transmits to the tibial tubercle, presenting as pain reported during activities that increase the stress on the tubercle, such as kneeling, squatting, kicking, or similar activities that increase the extensor force transmitted by the quadriceps. Patients localize pain to the anterior aspect of the proximal tibia and knee. Physical examination typically discloses tenderness over an enlarged tibial tubercle. The condition is diagnosed clinically; x- rays, if obtained, may show increased lucency in the area of the tibial tubercle. Treatment is through rest, cryotherapy, and non-steroidal anti-inflammatory medications, as the condition resolves with time and unloading. Incorrect Answers: A, B, D, and E. Chondromalacia (Choice A) as related to the knee refers to deterioration of cartilage along the posterior aspect of the patella. It is common in young athletes, especially runners, and presents with knee pain that is worse with bending. It can be differentiated from Osgood-Schlatter disease by the location of pain, whereas chondromalacia will not present with pain at the tibial tuberosity.
Ligamental tear (Choice B) is a broad term that in the context of the knee could describe damage to any of the collateral ligaments, such as the anterior or posterior cruciate or the medial or lateral collateral ligaments. Tear or rupture of these ligaments presents with pain which is worse when placing the affected ligament under strain, tenderness in the area of the injury, and laxity when evoking the motion restricted by the ligament itself. Osteochondritis (Choice D) describes the inflammation of bone or cartilage within a joint; it may al" " Exam Section 1: Item 2 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 40-year-old man is evaluated because his skin is extremely sensitive to sunlight. Exposure to the sun causes the formation of vesicles and blisters on the skin, which frequently take weeks to heal. He is diagnosed with a disorder caused by the increased synthesis of compounds in the skin that are subject to excitation by visible light. Which of the following biochemical pathways is most likely defective in this patient? A) Bile acid synthesis B) Bilirubin degradation C) Heme synthesis D) Melanin synthesis
E) Riboflavin metabolism - CORRECT ANSWER C.
Porphyria cutanea tarda is characterized by severe cutaneous photosensitivity with blistering and hyperpigmentation after exposure to sunlight and is the most common of the porphyrias. It is caused by decreased activity of uroporphyrinogen decarboxylase, an enzyme used to in the production of heme. The initial substrates for heme are glycine and succinyl-CoA. Their conversion to heme begins in the mitochondria with a rate limiting step catalyzed by aminolevulinate synthase. A series of additional steps then occurs which take place in the cellular cytoplasm. In one of these intermediate steps, uroporphyrinogen decarboxylase catalyzes the conversion of uroporphyrinogen III to coproporphyrinogen III. Not only will a deficiency in uroporphyrinogen decarboxylase prevent correct heme synthesis, it will also cause uroporphyrinogen III to accumulate. Accumulated uroporphyrinogen IIl is then deposited in the skin. Upon exposure to light of wavelength 400nm, the molecule enters an excited state and releases photons which in turn create reactive oxygen species within the skin. These reactive oxygen species damage the basement membrane, lipids, and proteins nearby resulting in dermoepidermal separation and blister formation. Incorrect Answers: A, B, D, and E. Bile acid synthesis (Choice A) uses cholesterol as the initial substrate. Cholesterol 7a-hydroxylase is the rate-limiting step in the creation of bile acids. Porphyrins are not intermediate byproducts of this pathway. Impaired bile acid production will lead to decreased intestinal absorption of lipids and fat-soluble vitamins, but not photosensitivity and blister formation.
Because LH stimulates the Leydig cells to produce testosterone, when LH concentration is decreased, testosterone concentrations will also decrease (Choice B). A medication which continuously increases testosterone would not be appropriate for use in prostate cancer as it is an androgen-dependent malignancy and would continue to grow under androgen stimulation. LH decreases rather than showing no change (Choice C) when" " Exam Section 1: Item 4 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 34-year-old woman comes to the physician because of a 10-year history of constipation. She usually has fewer than three bowel movements weekly. She often has bloating and cramping, and she has to strain and apply perineal pressure to defecate. She says that she does not have problems with sleep, appetite, or energy. Palpation of the abdomen produces diffuse discomfort; bowel sounds are present. Which of the following is the most likely cause of this patient's gastrointestinal symptoms? A) Colon polyps B) Congenital megacolon (Hirschsprung disease) C) Factitious disorder D) Gluten enteropathy E) Irritable bowel syndrome
F) Major depressive disorder - CORRECT ANSWER E.
Irritable bowel syndrome (IBS) is characterized by recurrent, intermittent abdominal pain and alteration of bowel habits as either a change in stool frequency or consistency. The abdominal pain may be either exacerbated or relieved by defecation and can vary widely in location and character. IBS commonly presents with intermittent episodes of diarrhea and/or constipation, often which alternate. When diarrhea does occur, it usually does so during waking hours which serves to differentiate it from other causes of diarrhea. It is most common in middle-aged women and the pathogenesis is unknown. It is not caused by a structural abnormality, and physical examination will show nonspecific abdominal discomfort rather than localized pain. Stress management may improve bowel habits in patients with irritable bowel syndrome, which is often associated with concomitant anxiety. If medication is needed, dicyclomine is an antispasmodic and diphenoxylate slows gut motility. Both are used in the management of irritable bowel syndrome. Incorrect Answers: A, B, C, D, and F. Colon polyps (Choice A) present in a variety of subtypes, from non-neoplastic polyps (eg, hamartomatous, mucosal, inflammatory, hyperplastic) to potentially malignant polyps (adenomatous, serrated). Polyps are typically asymptomatic and are only recognized after screening colonoscopy. They are not a common cause of chronic constipation. Inflammatory polyps may be seen in inflammatory bowel disease, but not irritable bowel syndrome.
Congenital megacolon (Hirschsprung disease) (Choice B), or intestinal aganglionosis, is caused by the congenital absence of the distal portion of the myenteric plexus, a part of the enteric nervous system located between the inner and outer layers of the muscularis externa. This often leads to a failure to pass stool within the first fe" " Exam Section 1: Item 5 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- Human gene fragments in appropriate vectors may be introduced into bacterial cells by transformation. Which of the following is most likely to be used to transfer cloned human genetic material to bacteria? A) DNA complexed with bacterial histones O B) Human chromosomal fragments C) Naked DNA D) Purified euchromatin
E) Purified heterochromatin - CORRECT ANSWER C.
Transformation describes the ability of bacteria to uptake and incorporate exogenous genetic material (naked DNA) from the environment. Following lysis of a cell DNA may exist extracellularly; a bacterium may uptake such material through the cell membrane. Transformation is one of three methods of horizontal gene transfer by which bacteria can acquire novel genes which may confer a survival benefit. Notably, Streptococcus pneumoniae and Haemophilus influenzae type B have demonstrated acquisition of genetic material by transformation. In order for transformation to occur, a bacterium must demonstrate competence (the ability to uptake such material). Competence occurs in states of stress such as starvation. Beyond transformation, horizontal gene transfer may also occur via conjugation (in which two cells in direct contact, typically involving a sex pilus), exchange material, and transduction (transfer of genetic material via a viral vector such as a bacteriophage). Incorrect Answers: A, B, D, and E. DNA complexed with bacterial histones (Choice A), human chromosomal fragments (Choice B), purified euchromatin (Choice D), and purified heterochromatin (Choice E) all describe fragments of DNA associated with additional protein sizes. The process of transformation requires naked DNA, which describes DNA that is not associated with proteins, lipids, or molecules that may shield it. exes and of variable Educational Objective: Transformation describes the ability of bacteria to uptake and incorporate genetic material (naked DNA) that is not associated with proteins or lipids from the environment. This mechanism may promote genetic diversity and acquisition of survival advantage. %3D Previous Next
Previous Next Score Report Lab Values Calculator Help Pause" " Exam Section 1: Item 7 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 12-year-old girl is brought to the emergency department 15 minutes after she accidentally sliced her left palm with a knife. Physical examination shows a 2-cm laceration over the left palm. The wound is cleansed and sutured. One week later, the sutures are removed. At this time, which of the following factors is most instrumental in the migration of fibroblasts into the area of wound healing? A) Collagen B) Fibronectin C) Нераrin D) Immunoglobulin
O E) Plasminogen - CORRECT ANSWER B.
Wound healing occurs via a staged process. In early wound healing, platelet aggregation and platelet plug formation occur to achieve hemostasis. In the subsequent 1 to 7 days, neutrophils and macrophages infiltrate the area and release growth factors and cytokines that stimulate fibroblast proliferation. Fibronectin is essential for fibroblast migration by providing a pathway for migration during wound healing. Fibroblasts bind to peptide sequences within fibronectin, which guide them to the site of healing. Granulation tissue forms as collagen is deposited into the area by fibroblasts and neovascularization begins to occur. During this time, wound edges contract from the action of myofibroblasts. Epidermal cells migrate across the newly deposited collagen matrix to reconstitute normal skin appearance. In the following weeks and months, scar formation and remodeling occur via metalloproteinase-mediated collagen breakdown. Incorrect Answers: A, C, D, and E. Collagen (Choice A) is synthesized by fibroblasts and contributes to scar formation in the process of wound healing. Dermal collagen fibers increase as a result of scarring. While the majority of collagen fibers in healthy skin are type I collagen, scarring is initially created by type III collagen. Heparin (Choice C) is a common anticoagulant that potentiates the action of antithrombin III to inhibit multiple coagulation factors. It does not relate to fibroblast migration in wound healing. Immunoglobulins (Choice D) are found on B lymphocyte membranes or are secreted into the serum by plasma cells to recognize antigens and activate the immune system in response to a pathogen.
Plasminogen (Choice E) is converted to plasmin, which subsequently degrades fibrin clots leading to clot dissolution. Plasminogen is made in the liver and its role is to degrade and prevent" " Exam Section 1: Item 8 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- The local health department is investigating an outbreak of acute hepatitis A in two city districts by reviewing the medical records at a health center in each district. The investigators plan to analyze the clinical and epidemiologic characteristics of patients who tested positive for hepatitis A serum IgM antibody compared with characteristics of those who tested negative for the antibody. Which of the following best describes this study design? A) Case series B) Case-control study C) Prospective study D) Randomized trial
E) Retrospective cohort - CORRECT ANSWER B.
This study compares one group of patients with an outcome under study (seropositive for Hepatitis A IgM antibody) (cases) against a second matched group without that outcome (controls) and identifies the associated exposure within each group. This study design is known as a case-control study. Case-control studies can be conducted in a prospective or retrospective manner but are always observational studies. By grouping patients by outcome and comparing differences in the odds of exposure, case-control studies can detect associations between exposure and outcome, such as exposure to certain risk factors and outcome of contracting hepatitis A as in this study. This is described statistically as an odds ratio (OR). Two unrelated variables will have an OR of 1.0, whereas positive association between an exposure and an outcome will have an OR greater than 1.0 and negatively associated variables will have an OR less than 1.0. Case-control studies are therefore capable of establishing association between exposure and outcome, but they do not establish causality. Incorrect Answers: A, C, D, and E. A case series study (Choice A) is a descriptive study that describes the history, possible exposures, and clinical findings of a group of patients with a similar diagnosis. Case series are non-analytic studies. They do not test a hypothesis and do not generally contain a control group. A prospective study (Choice C) is one in which one group of patients experiences an intervention or exposure and an associated control group does not. The two groups are followed and the desired outcome tracked. A randomized trial (Choice D) is a stringent type of prospective study wherein patients are randomly assigned to receive a particular intervention. The intervention may be compared against placebo therapy or against standard therapy, depend" " Exam Section 1: Item 9 of 50
- The graph shows the mean steady state plasma concentration of Drug X as a function of time in a subject who has normal weight (solid curve) and a subject who is obese (dashed curve). Both subjects take 10 mg of Drug X daily. Which of the following best describes the disposition of Drug X in the obese patient compared with the patient who has normal weight? A) Greater volume of distribution B) Higher clearance C) Lower bioavailability D) Slower absorption rate E) Shorter half-life 1 3 4 6 7
Time (days) - CORRECT ANSWER A.
Volume of distribution is the theoretical volume in which a drug exists given its plasma concentration following a dose of medication. There are three main compartments into which a medication can distribute: the intravascular compartment, the interstitial compartment, and the intracellular compartment (including fat). With an increased volume of distribution, the same dose of medication will lead to a smaller plasma concentration (ie, it will distribute more widely into tissue), and it will take longer for the medication to reach a steady state within the plasma. Large molecules or protein-bound molecules generally remain within the vasculature and quickly reach a steady state concentration given the relatively low volume of the intravascular compartment. Smaller hydrophilic molecules tend to move into the interstitial space, which increases their volume of distribution and increases the amount of time it takes for the medication to reach a steady state concentration. Small lipophilic molecules, however, exhibit the largest volume of distribution as they are commonly taken up by adipocytes, which greatly increases the volume in which they are distributed. Therefore, it takes these molecules longer to reach a steady state concentration, especially in obese patients in which the volume of distribution is even greater given the presence of increased fat stores, as seen in this graph. Incorrect Answers: B, C, D, and E. Higher clearance (Choice B) of a medication indicates that more medication is removed from the body in a given period of time. Differences in clearance are typically because of changes in hepatic or renal function and are commonly displayed in a graph that shows the decline in drug concentration. An increase in clearance with the same volume of distribution would require a higher maintenance dose to reac" " Exam Section 1: Item 11 of 50 National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
- A 26-year-old man comes to the physician because of fever, cough, chest pain, and malaise for 2 weeks. He moved to central California 6 months ago. A complete blood count shows mild eosinophilia. A chest x-ray shows patchy bronchopneumonia. Culture of the sputum grows a mold with the morphology shown in the photomicrograph, with the arrow indicating the infectious particle. Which of the following is the most likely causal organism? A) Actinomyces israelii B) Coccidioides immitis C) Histoplasma capsulatum D) Legionella pneumophila E) Mycobacterium tuberculosis OF) Nocardia brasiliensis G) Staphylococcus aureus
H) Streptococcus pneumoniae - CORRECT ANSWER B.
Coccidioides immitis is an endemic fungus of the Southwestern United States and central valley of California that typically causes coccidioidomycosis, a self-limited respiratory illness. Signs and symptoms include fever, fatigue, cough, arthralgia, and myalgia. Patients may also present with erythema nodosum. Coccidioidomycosis can potentially present with disseminated disease, especially in immunocompromised patients, and cause infections of the skin, bone, and central nervous system. Silver stain of sputum or tissue biopsy demonstrates large spherules containing endospores. Diagnosis can be facilitated with enzyme-linked immunosorbent assay (ELISA) testing and be confirmed with polymerase chain reaction. Treatment is with oral or intravenous antifungals, including agents from the azole or polyene classes. Incorrect Answers: A, C, D, E, F, G, and H. Actinomyces israelii (Choice A) is a Gram-positive, anaerobic bacillus that forms branching filaments and yellow granules. It typically causes abscesses of the head and neck, often with draining fistulous tracts. Histoplasma capsulatum (Choice C) is a fungus native to the Ohio river and Mississippi river valleys that can cause pneumonia and is spread by the droppings of birds or bats. It is identifiable as oval yeasts within macrophages. Legionella pneumophila (Choice D) is a Gram-negative bacillus that is transmitted primarily through aerosols from water sources. It causes Legionnaire disease, characterized by fever, pneumonia, and gastrointestinal symptoms. It can be identified by positive staining with silver stains and its fastidious nature, requiring culture on charcoal yeast extract with supplemental iron and cysteine. Mycobacterium tuberculosis (Choice E) is an acid-fast bacillus that causes tuberculosis. It is identifiable by its thick, waxy capsule, positive ac" " Exam Section 1: Item 12 of 50
- A 38-year-old woman with asthma comes to the physician for advice concerning contraception. She is sexually active with one partner, and they use condoms inconsistently. Current medications include inhalational fluticasone and albuterol. She has smoked one-half pack of cigarettes daily for 20 years and drinks two alcoholic beverages daily. She does not use illicit drugs. Her maternal grandmother developed breast cancer at the age of 58 years. She is 157 cm (5 ft 2 in) tall and weighs 82 kg (180 lb); BMI is 33 kg/m2 Her vital signs are within normal limits. Physical examination shows no other abnormalities. This patient should be advised to avoid the use of an oral contraceptive because of which of the following historical factors? A) Age B) Alcohol use C) Asthma D) Family history E) Obesity
F) Tobacc - CORRECT ANSWER F.
Combined oral contraceptive pills (OCPS) contain a combination of estrogen and progesterone. They are primarily used for contraceptive purposes but can also be used in a variety of gynecologic disorders, such as polycystic ovarian syndrome (PCOS), menorrhagia, and endometriosis. A sustained release of progestin and estrogen prevents ovulation and causes thickening of the cervical mucus along with thinning of the endometrial layer by inhibiting the release of gonadotropin-releasing hormone, follicle- stimulating hormone, and luteinizing hormone. OCPS are typically administered as a daily pill for three weeks, followed by a daily placebo pill for one week, during which time withdrawal bleeding occurs. They are associated with increased hypercoagulability and are therefore contraindicated in patients with a history of deep venous thrombosis, pulmonary embolism, stroke, or myocardial infarction. They are also contraindicated in patients who are 35 years of age or older and concomitantly smoke 15 or more cigarettes per day, along with patients diagnosed with hypertension, migraine with aura, severe cirrhosis, and breast cancer. Common adverse effects include nausea, breast tenderness, irregular menstrual periods, and a mildly delayed return to fertility following cessation. OCPS are contraindicated in this patient caused by her tobacco use. Incorrect Answers: A, B, C, D, and E. Age (Choice A) can increase the risks associated with OCPS, as there is an increased baseline risk for cardiovascular disease. However, this patient is only 38 years old, and age alone is not a contraindication to OCP use without smoking history. Alcohol use (Choice B) can preclude the use of OCPS if severe and associated with consequent cirrhosis, as they are generally contraindicated in severe decompensated cirrhosis. However, alcohol use alone" " Exam Section 1: Item 14 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 27-year-old man with AIDS comes to the physician because of a 6-week history of progressive memory loss, imbalance, clumsiness, and difficulty finding words. The symptoms began with an inability to concentrate 3 months ago. He is not adherent to combination antiretroviral therapy and recently recovered from Pneumocystis jirovecii (formerly P. carinii) pneumonia. An MRI shows diffuse, poorly defined, bilateral hyperintensities within cerebral white matter. A stereotactic biopsy specimen shown in the photomicrograph depicts cells scattered predominantly along the perivascular spaces. Which of the following is the most likely diagnosis? A) Cryptosporidiosis B) HIV encephalopathy C) HIV protease inhibitor toxicity O D) Lymphoma
E) P. jirovecii infection - CORRECT ANSWER B.
HIV encephalopathy is the most likely diagnosis in this patient with AIDS, progressive memory loss, and motor deficits who does not adhere to antiretroviral therapy. HIV encephalopathy is a diagnosis of exclusion in patients with HIV, and other causes of encephalopathy such as toxoplasmosis, meningitis, encephalitis, bacterial abscess, progressive multifocal leukoencephalopathy (PML), or primary central nervous system (CNS) lymphoma should be ruled out. The classic triad of HIV encephalopathy involves movement disorders, psychomotor impairment, and memory deficits. While it can occasionally be confused with PML, patients with PML tend to have a more rapid disease progression, focal deficits, and different findings on MRI. In HIV encephalopathy, the MRI demonstrates multiple, symmetric, and poorly demarcated T2 hyperintense lesions scattered in the subcortical white matter. Brain biopsy characteristically demonstrates microglial nodules with multinucleated giant cells as in this case. Incorrect Answers: A, C, D, and E. Cryptosporidiosis (Choice A) is caused by Cryptosporidium parvum that presents with severe diarrhea in patients with AIDS. Symptoms include fever, weight loss, symptoms of dehydration and orthostasis, severe, watery diarrhea, cramping abdominal pain, nausea, and vomiting. Disseminated infection can involve the lungs and liver but encephalopathy or encephalitis does not occur. HIV protease inhibitor toxicity (Choice C) can present acutely with nausea and vomiting, but long-term complications commonly include lipodystrophy and increased cardiovascular risk. They do not cause encephalopathy. Lymphoma (Choice D) in patients with AIDS can take on many forms, but primary CNS lymphoma is common. It often presents with seizures, lethargy, subacute memory loss, and headache. Physical examination may show neurol" " Exam Section 1: Item 15 of 50 National Board of Medical Examiners®
A
•B
E•
C
D
Left ventricular volume (mL) A) B) C) D)
E) - CORRECT ANSWER D.
Nitroprusside is an intravenous, titratable vasodilator that can be used for the treatment of hypertensive emergencies. It breaks down in circulation to release nitric oxide, which in turn activates guanylate cyclase in vascular smooth muscle to result in vascular smooth muscle relaxation and vasodilation via a cyclic GMP pathway. It typically induces a reflex tachycardia. Sodium nitroprusside preferentially dilates arterial vessels over venous vessels, resulting in a decrease in afterload without significant change in preload. An isolated decrease in afterload results in a shortened pressure-volume loop (less left ventricular pressure is needed to open the aortic valve) and a decreased end-systolic left ventricular volume (because of an increased stroke volume and ejection fraction). The associated end-systolic pressure point on this graph is represented by point D. Incorrect Answers: A, B, C, and E. Choice A represents a point that may be observed if afterload is increased and cardiac contractility is increased. The left ventricular pressure needed to open the aortic valve is increased, and the increased contractility maintains the stroke volume to result in the same end-systolic left ventricular volume as the control. Choice B represents the end-systolic pressure point associated with an isolated increase in afterload. The left ventricular pressure needed to open the aortic valve is increased and the stroke volume is reduced, resulting in an increased end-systolic left ventricular volume. Choice C represents an end-systolic pressure point that may be seen in the case of decreased afterload and decreased cardiac contractility, with reduced end-systolic left ventricular pressure and a reduced stroke volume resulting in increased end-systolic left ventricular volume. Choice E represents a point that may occur with a" " Exam Section 1: Item 17 of 50
National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- The patient whose cardiac function is illustrated most likely has which of the following? Normal A) Arteriovenous malformation B) Cardiac tamponade C) Congestive heart failure Patient D) Cor pulmonale E) Restrictive cardiomyopathy Left ventricular end-diastolic
volume - CORRECT ANSWER C.
The Frank-Starling mechanism describes the phenomena by which cardiac output is dependent on the amount of cardiomyocyte fiber stretch prior to contraction, as represented by the left ventricular end-diastolic volume. A greater pre-contraction stretch results in a greater force of contraction (to a point), and the relationship is demonstrated by Frank-Starling curves. A given Frank-Starling curve applies for constant afterload and inotropy. Changes in afterload and/or inotropy shift the curve up or down. This patient has a Frank-Starling curve that is shifted down, indicating that for a given preload, there is reduced cardiac output relative to normal. This may occur in decreased inotropic states such as congestive heart failure, with the administration of negative inotropes, or in the setting of increased afterload. The curve shifts up in positive inotropic states and/or with decreased afterload. Incorrect Answers: A, B, D, and E. Arteriovenous malformation (Choice A) results in low-resistance, high-volume flow of blood from the arterial to the venous system with greatly increased venous return. The increase in preload causes a greater distension in the cardiomyocyte fibers at the end of diastole, which results in increased cardiac output per the Frank-Starling relationship. Cardiac tamponade (Choice B) result in decreased ventricular filling because of compression of the heart by fluid in the pericardium. In the absence of other factors affecting afterload or cardiac contractility, the Frank-Starling curve would not be depressed. Cor pulmonale (Choice D) describes right ventricular failure resulting from chronic pulmonary hypertension. Left ventricular contractility and afterload are not affected, and the Frank-Starling curve for the left ventricle would not shift. Restrictive cardiomyopathy (Choice E) results in" " Exam Section 1: Item 18 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 28-year-old woman has had fatigue and heavy menstrual periods during the past year. She is a vegetarian who eats eggs and dairy products. Her diet contains little fruit. Which of the following erythrocyte types is most likely to be present on a peripheral
shown. A nitroblue tetrazolium test shows deficient reduction by granulocytes. The axillary mass
is incised and drained, and culture of the fluid grows Staphylococcus aureus - CORRECT
ANSWER B.
Chronic granulomatous disease (CGD) is the most likely diagnosis in this patient with a Staphylococcus aureus abscess, history of prior similar infections, and an abnormal nitroblue tetrazolium test. CGD is defined by deficiency of the NADPH oxidase complex, which is essential for normal neutrophil intracellular killing of pathogens. NADPH oxidase uses oxygen as a substrate for the generation of free radicals (superoxide anions). Free radical oxygen species are subsequently used for the creation of hydrogen peroxide and hypochlorous acid. Activation of this pathway leads to the respiratory burst which results in bacterial death. Deficiency of NADPH oxidase renders phagocytes incapable of neutralizing catalase-positive bacteria, which are capable of neutralizing their own hydrogen peroxide, thus leaving the host cells without the substrate necessary to complete the respiratory burst. Diagnosis is made by an abnormal dihydrorhodamine test or a nitroblue tetrazolium reduction test. In this latter test, normal phagocytes use the action of NADPH to reduce nitroblue, which leads to a color change from yellow to blue. Patients with CGD will not demonstrate color change. Recurrent pneumonia is the most common presenting infection in patients with CGD, and the most common infecting bacteria include Staphylococcus species, Aspergillus species, Burkholderia cepacia, and Nocardia species. Patients with CGD are also at risk for fungal infections, especially Aspergillus species. Incorrect Answers: A, C, D, and E. presentingChédiak-Higashi syndrome (Choice A) is a rare, autosomal recessive disorder of the immune system caused by mutations in the lysosomal trafficking regulator gene (LYST) that encodes a protein essential for normal formation and transportation of lysosomes within the cell. The clinical manifestations include freq" " Exam Section 1: Item 20 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- A 67-year-old white woman undergoes punch biopsy of an urticarial lesion on her back. When the biopsy specimen container is received in the laboratory, it is determined that it contains two specimens instead of one. Review of the additional specimens received from the physician's office indicates that specimens from two separate patients were inadvertently shipped in the same container. The other specimen is from the back of a dark- skinned, 58-year-old Nigerian woman. An increase in which of the following in the specimen from the Nigerian patient is most likely to differentiate these two specimens? A) Number of melanocytes B) Number of melanophages C) Number of melanosomes
D) Size of melanocytes - CORRECT ANSWER C.
Melanin is a pigment made within a specialized cellular organelle called a melanosome found in melanocytes, which are dendritic cell derivatives that reside in the basal layer of the epidermis. Melanocytes are derived from neural crest cells, which originate at the dorsal neural tube. During embryologic development, they migrate from dorsal to ventral, and then to the epidermis. The initial substrate in the creation of melanin is the amino acid tyrosine. After producing melanin from tyrosine, the melanosomes are transferred to the surrounding keratinocytes. The variation in skin tones seen in different ethnic groups is based on the number of the melanosomes and the distribution of melanin within them in the keratinocytes, not the number of melanocytes themselves. In patients with darker skin, the melanosomes are more numerous and more densely packed with melanin. In patients with lighter skin, the melanin is distributed with less density, and there are fewer melanosomes. Melanin production is regulated in part by melanocyte-stimulating hormone (MSH). MSH is a byproduct of proopiomelanocortin (POMC) which also produces adrenocorticotropic hormone (ACTH). In adrenal insufficiency, stimulation of ACTH production by POMC simultaneously produces MSH, leading to diffuse hyperpigmentation in affected patients. Incorrect Answers: A, B, and D. Neither the number of melanocytes (Choice A) nor their size (Choice D) differs between patients with different skin types. Increased number, size, and nuclear/cytoplasmic ratio of melanocytes would be seen in melanoma, a neoplasm of melanocytes. Lesions concerning for melanoma are characterized clinically by asymmetry, irregular-appearing borders, variable coloration, a diameter greater than 6 mm, and rapid evolution in characteristics. Melanophages are macrophages which have taken up" " Exam Section 1: Item 21 of 50 National Board of Medical Examiners® Comprehensive Basic Science Self-Assessment
- An investigator is studying the adverse effects of a proteasome inhibitor, bortezomib, on immune responses. Bortezomib is administered to a group of patients with relapsed multiple myeloma, and immune responses are observed. Which of the following immunologic processes is primarily affected by this drug? A) Activation of the complement cascade B) Activation of perforin C) Presentation of antigens to CD8+ T lymphocytes D) Secretion of histamine by mast cells
E) Secretion of interleukin-1 (IL-1) by macrophages - CORRECT ANSWER C.
Presentation of antigens to CD8+ T lymphocytes would be affected by the use of the proteasome inhibitor bortezomib. Proteasomes are large proteases with numerous domains that are present in both the cytoplasm and the nucleus. They are made of a and B
