Uworld21

Question 1

What is catscratch disease?

Answer 1

caused by Bartonella henselae, a gram negative coccobacillus transmitted by a cat scratch or bite.

Patients commonly present with tender lymphadenopathy proximal to the inoculation site (eg, axillary, epitrochlear lymph nodes).

Lymph node histopathology often shows necrotizing granulomas and stellate shaped microabscesses.

Question 2

What is leptin?

Answer 2

Leptin is a protein hormone produced by adipocytes in proportion to the quantity of fat stored.

Leptin acts on the arcuate nucleus of the hypothalamus to inhibit production of neuropeptide Y (decreasing appetite) and stimulate production of alpha-MSH (increasing satiety).

Mutations in the leptin gene or receptor result in hyperphagia and profound obesity

Question 3

Damage to the subthalamic nucleus causes?

Answer 3

The subthalamic nucleus plays an important role in the modulation of basal ganglia output.

Damage to this structure (eg, due to lacunar stroke) may result in contralateral hemiballism: wild, involuntary, large-amplitude, flinging movements of the proximal limbs (arm and/or leg) on one side of the body

Question 4

What test is specific for EBV?

Answer 4

Epstein Barr virus commonly infects B cells, stimulating them to proliferate continuously (transformation or immortalization).

EBV is an oncogenic virus that promotes polyclonal B cell proliferation and heterophile antibody production.

The heterophile antibody test is sensitive and highly specific for EBV infection

Question 5

Temporal lesions can cause what eye issue?

Answer 5

The inferior optic radiations travel through the temporal lobe in the Meyer loop.

They carry information from the inferior retina, which covers the superior visual field. Therefore, temporal lobe lesions can result in contralateral homonymous superior quadrantanopia.

Question 6

What is gestational thrombocytopenia?

Answer 6

common in the third trimester and is typically mild, asymptomatic, and not associated with other laboratory abnormalities. It occurs due to hemodilution (ie, maternal plasma volume expansion) and increased sequestration/consumption of platelets in the placenta.

Question 7

What drugs have the highest risk for drug induced lupus?

Answer 7

Procainamide and hydralazine and isoniazid.

Drug induced lupus has positive ANA and anti-histone antibodies.

Question 8

Classic galactosemia results from deficiency of?

Answer 8

galactose-1-phosphate uridyl transferase.

Clinical features: vomitting, lethargy, jaundice, and E coli sepsis.

Cessation of breastfeeding and switching to soy milk based formula is recommended

Question 9

What is negative predictive value?

Answer 9

represents the probability of not having a disease given a negative test result.

NPV is inversely proportional to the prevalence of a disease.

When a patient has characteristics similar to the overall population (eg, age, sex, risk factor status), the disease prevalence is a valid estimate of the pretest probability of disease

Question 10

The infusion of excessive normal saline (sodium chloride) is a common cause of?

Answer 10

nonanion gap metabolic acidosis.

The excess intravascular chloride causes intracellular shifting of bicarbonate, reducing serum bicarbonate and decreasing blood pH

Question 11

What is renal artery stenosis?

Answer 11

Marked unilateral kidney atrophy is suggestive of renal artery stenosis.

It occurs in elderly people due to atherosclerotic narrowing of the renal artery and is often seen in association with other atherosclerotic risk factors or diseases (eg, chronic mesenteric ischemia, coronary artery disease, peripheral vascular disease).

Hypertension and abdominal and flank bruits are often present.

Question 12

What is hypoglycemia characterized by?

Answer 12

tremor, diaphoresis, and confusion in association with a low blood glucose level and resolution of symptoms when the blood glucose level is corrected.

Hypoglycemia with elevated insulin and low C peptide levels suggests exogenous insulin injection, whereas elevated C peptide suggests an insulin secretagogue or insulin secreting tumor

Question 13

What is paroxysmal noctural hemoglobinuria?

Answer 13

Triad of hemolytic anemia, hypercoagulability, and pancytopenia.

PNH results from an acquired mutation in the PIGA gene that causes absence of the glycosylphosphatidylinosital anchor and associated deficiency of CD55 and CD59 complement inhibitor proteins

Question 14

What can cause watershed infarctions?

Answer 14

Sustained cerebral hypoperfusion (eg, hypotension, shock) may cause cerebral ischemia and watershed infarction.

These watershed zones are located at the borders between areas perfused by the anterior, middle, and posterior cerebral arteries and typically appear as symmetric, bilateral wedge shaped strips of necrosis over the cerebral convexity, parallel and adjacent to the interhemispheric fissure.

Question 15

Which heme drugs effect thrombin time and which do not?

Answer 15

Direct factor Xa inhibitors (apixaban, rivaroxaban) increase the prothromin and activated thromboplastin times but do not affect the thrombin time.

Unfractionated heparin and direct thrombin inhibitors (dabigatran) prolong the thrombin time.

Question 16

Why does appendicitis cause pain?

Answer 16

Appendicitis causes dull visceral pain at the umbilicus due to afferent pain fibers entering at the T10 level in the spinal cord.

Progressive inflammation in the appendix irritates the parietal peritoneum and abdominal wall to cause more severe somatic pain shifting from the umbilicus to McBurney’s point (2/3 of the distance from the umbilicus to the anterior superior iliac spine)

Question 17

What is serum sickness?

Answer 17

an immune complex mediated type III HSR that typically forms 5-14 days after exposure to foreign proteins in an antitoxin, antivenom, monoclonal antibody, or vaccine.

Patients typically develop fever, urticarial rash, and arthralgia that resolve spontaneously over days as the immune complexes are cleared by the mononuclear phagocyte system

Question 18

Which holosystolic murmur increases in intensity on inspiration?

Answer 18

tricuspid regurgitation.

Question 19

CD4 binds which HIV receptor

Answer 19

gp120

Question 20

CD21 likes to bind which receptor

Answer 20

epstein barr gp350

Question 21

erythrocyte P antigen likes to bind?

Answer 21

parvovirus B19

Question 22

What is ovarian torsion?

Answer 22

typically occurs in reproductive aged women due to rotation of the ovary around the infundibulopelvic (suspensory) and uteroovarian ligaments.

Patietns typically have sudden onset unilateral pelvic pain and a tender adnexal mass.

Question 23

MOA of phenoxybenzamine

Answer 23

irreversible alpha 1 and 2 antagonist that effectively reduces the arterial vasoconstriction induced by norepinephrine

Because phenoxybenzamine is an irreversible antagonist, even very high concentrations of norepi, such as in pheochromocytoma, cannot overcome its effects

Question 24

What leads to muscle fiber type grouping?

Answer 24

With muscle denervation and reinnervation, nerve fiber collateral sprouting results in adjacent muscle fibers being innervated by the same neuron.

This leads to loss of the normal histologic checkerboard pattern of type 1 and type 2 muscle fibers and results in muscle fiber type grouping

Question 25

What is Ewing sarcoma?

Answer 25

malignant bone tumor that typically arises in the long bones or pelvis in children and often mets to the lungs. Imaging: poorly defined, lytic lesion with an onion skin periosteal reaction. Histopath: sheets of uniform small round blue tumor cells

Question 26

Thiazide and loop diuretics electrolytes status

Answer 26

Thiazide and loop diuretics causes significant volume depletion, activating the renin-angiotensin-aldosterone system, which can lead to hypokalemia and metabolic alkalosis. Thiazide diuretics are more likely to cause hyponatremia and hypercalcemia; loops cause hypocalemia

Question 27

How does systemic sclerosis effect the esophagus?

Answer 27

may result in esophageal dysmotility and incompetence of the lower esophageal sphincter due to atrophy and fibrous replacement of the esophageal muscularis. This can cause GERD with an increase risk of Barrett esophagus and stricture formation

Question 28

Thiazide diuretics, espically metolazone, potentiate the diuretic effect of loop diuretics (eg, furosemide) by?

Answer 28

blocking the reabsorption of the increased distal tubular sodium delivery caused by loop diuretics

Question 29

Elevated intracranial pressure in the absence of an intracranial mass lesion or ventriculomegaly is suggestive of?

Answer 29

decreased resorption of cerebrospinal fluid. This often occurs when the cerebral venous sinus system drainage is impaired due to either idiopathic intracranial hypertension or cerebral venous sinus thrombosis

Question 30

Why is drainage of an empyema difficult?

Answer 30

Empyema involves bacterial invasion of the intrapleural space with progressive inflammation, pus accumulation, and organized fibrosis. Drainage with a chest tube is often difficult due to loculations and high viscosity, but it can be aided by the intrapleural administration of a fibrinolytic agent (eg, tissue plasminogen activator) in combination with a nucleic acic cleaving enzyme (ie, deoxyribonuclease)

Question 31

What is the most common complication of bicuspid aortic valves?

Answer 31

aortic stenosis. Patients with bicuspid aortic valves develop clinically significant aortic stenosis on average around age 50. In comparison, senile calcific stenosis of normal aortic valves generally becomes symptomatic age >65

Question 32

What kind of laxative is polyethylene glycol?

Answer 32

an osmotic laxative. Primary lactose intolerance is associated with the inability to digest lactose. The high osmotic load from intraluminal accumulation of lactose can lead to watery diarrhea.

Question 33

How can Turner syndrome women get pregnant?

Answer 33

In vitro fertilization used a donated ovum is the most promising means of achieving pregnancy in a women with Turner syndrome. Pregnancy can occasionally occur spontaneously in some patients with Turner syndrome, but the risk of spontanous abortion, Down syndrome and Turner syndrome are all increased in such cases.

Question 34

Acute myocarditis is most commonly caused by?

Answer 34

a viral infection (coxsackie, adenovirus, influenza) It often resolves without noticeable symptoms, but patients can develop serious complications, including decompensated heart failure due to dilated cardiomyopathy or sudden cardiac death due to ventricular arrhythmia. Histopath: myocyte necrosis with inflammatory mononuclear infiltrate

Question 35

Lupus nephritis occurs due to?

Answer 35

SLE is an autoimmune disease characterized by the formation of antinuclear antibodies (anti-DNA antibodies) Lupus nephritis occurs primarily due to the formation of immune complexes containing DNA and anti-DNA in the circulation. These are deposited in the glomerulus where they result in complement activation, recruitment of inflammatory cells, and renal injury (type III HSR)

Question 36

What is the most common neurologic complication of varicella zoster virus infection?

Answer 36

Postherpetic neuralgia

Question 37

What is a thyroglossal duct cyst?

Answer 37

Failed atrophy of the thyroglossal duct in utero can result in thyroglossal duct cysts that can be located anywhere along the path of thyroid descent (from the tongue base to the thyroid base to the thyroid isthmus). Anterior midline neck mass that moves superiorly with swallowing or tongue protrusion.

Question 38

Down syndrome is commonly caused by?

Answer 38

Most commonly caused by maternal meiotic nondisjunction, a process by which the fetus receives 3 full copies of chromosome 21. Dysmorphic features (flat facial profile, protruding tongue, small ears, upslanting palpebral fissures) and cardiac defects (eg, endocardial cushion defects) are characteristics.

Question 39

Which cancer is associated with vinyl chloride?

Answer 39

Hepatic angiosarcoma is an aggressive vascular malignancy associated with exposure to carcinogens (eg, vinyl chloride). The tumor cells express CD31 (ie, platelet endothelial cell adhesion molecule [PECAM1], an endothelial cell marker important for leukocyte transmigration

Question 40

Which rotator cuff muscles are responsible for external rotation?

Answer 40

The rotator cuff muscles attach to the proximal humerus and move the arm at the shoulder. Infraspinatus and tere minor are primarily responsible for external rotation. When one is torn, the other hypertrophies to compensate, resulting in preserved strength in external rotation.

Question 41

What is relative risk?

Answer 41

the measure of assoication between the exposure to a risk factor or treatment and an outcome or disease and is commonly used in cohort studies. The interpretation of the RR depends on which groups are identified as exposed and unexposed.

Question 42

Hypokalemia in an otherwise healthy young adult with a normal BMI and preoccupation with body size is concerning for?

Answer 42

self induced vomiting associated with bulimia nervosa. PE for bulimia nervosa: tachycardia, hypotension, painless parotid gland swelling, calluses or scarring on the dorsum of the hand, and erosion of dental enamel.

Question 43

MOA of raloxifene

Answer 43

a selective estrogen receptor modulator that has estrogen agonist activity on bone and decreases bone resorption. Medicines with estrogen agonist activity, including SERMS, oral contraceptives, and hormone replacement therapy, can increase the risk for venous thromboembolism

Question 44

Regulation of the Gas-MAPK signal transduction pathway requires a balance between?

Answer 44

active (GTP-bound) and inactive (GDP-bound) Ras proteins. RAS gene mutations, which result in constitutively activated Ras proteins, are implicated in the development of malignant tumors.

Question 45

What is calcineurin?

Answer 45

an essential protein in the activation of IL-2, which promotes the growth and differentiation of T cells. Immunosuppressants such as cyclosporine and tacrolimus work by inhibiting calcineurin activation

Question 46

When can a small bowel obstruction occur?

Answer 46

Occurs when a mechanical or functional obstruction disrupts the normal flow of intestinal intraluminal contents. A herniated bowel loop (eg, inguinal hernia) can cause SBO if it becomes trapped (ie, incarcerated) outside the peritoneal cavity

Question 47

What is cirrhosis?

Answer 47

characterized by diffuse hepatic fibrosis with replacement of the normal lobular architecture by fibrous-lined parenchymal nodules. Chronic viral hepatitis (eg, Hep B and C), alcohol, hemochromatosis, and nonalcoholic fatty liver disease are the most common caused of cirrhosis in the US

Question 48

What is alpha-1 antitrypsin deficiency?

Answer 48

Alpha-1 antitrypsin is a serine protease inhibitor that regulates the activity of elastase in the lung, Inherited deficiency of the AAT leads to alveolar destruction and panacinar emphysema; in addition, accumulation of improperly folded AAT proteins in hepatocytes can lead to liver dysfunction and cirrhosis in some patients.

Question 49

What is ubiquitin?

Answer 49

a protein that undergoes attachment to other proteins, labeling them for degradation by proteasomes. Impairment of the ubiquitin-proteasome system leads to the accumulation of misfolded proteins, which can contribute to the development of neurodegenerative disorders (eg, Parkinson disease)

Question 50

What is pancreatic ductal adenocarcinoma?

Answer 50

the most common pancreatic malignancy and typically presents with epigastric pain, weight loss, jaundice (more common if in the pancreatic head), or back pain (more common if in the pancreatic body/tail) xray: ill-defined hypoattenuating lesion within the pancreatic parenchyma Micro: haphazardly arranged pleomorphic glandular cells surrounded by dense stromal fibrosis (eg, desmoplasia)

Question 51

What is acute dystonic reaction?

Answer 51

sudden, involuntary contraction of a major muscle group. It is a type of extrapyramidal symptom and a common adverse effect of antipsychotic medications, particularly high potency, first generation antipsychotics such as haloperidol

Question 52

What is bipolar I disorder?

Answer 52

diagnosed in patients with >1 episodes of mania. Manic episodes are characterized by elevated/irritable mood, impulsivity, hyperactivity, decreased need for sleep,pressured speech, and grandiosity and may occur with psychotic features

Question 53

How does high levels of cortisol cause hypertension?

Answer 53

High levels of cortisol, as seen in patients with Cushing syndrome, frequently cause hypertension due to the increased production of angiotensinogen, adrenergic hypersensitivity, and activation of renal mineralocorticoid receptors, which induces sodium reabsorption. The combined effects leads to expanded blood volume and increase systemic vascular resistance.

Question 54

When does manifestations arise in malaria?

Answer 54

generally asymptomatic for 1-4 weeks after transmission. Manifestations arise once the pathogen lyses erythrocytes, which releases inflammatory cytokines. Initial manifestations typically include periods of high fever and nonspecific, flu like symptoms

Question 55

Chronic rhinosinusitis with nasal polyposis in child should prompt evaluation for?

Answer 55

cystic fibrosis, especially when signs of pancreatic insufficiency (eg, loose stools, failure to thrive, weight loss) are present

Question 56

MOA of angiotensin II receptor blockers (losartan)

Answer 56

work by blocking angiotensin II type 1 receptors, inhibiting the effects of angiotensin II. This results in arterial vasodilation and decreased aldosterone secretion. The resulting fall in blood pressure increases renin, angiotensin I and angiotensin II levels. ARBs do not affect the activity of angiotensin-converting enzyme, and therefore they do not affect bradykinin degradation and do not cause cough.

Question 57

How can right ventricular infarction (right sided heart failure) lead to shock?

Answer 57

Right ventricular infarction (right sided heart failure) can lead to shock via impaired forward blood flow to the left heart, which lowers left-sided preload (decreased pulmonary capillary wedge pressure) and decreases cardiac output. The reduced right ventricular output also raises right atrial and central venous pressure.

Question 58

What are the watershed areas in the colon?

Answer 58

Severe systemic hypotension (eg, shock) is most likely to causes ischemia first in areas of high metabolic demand (eg, hippocampus) or watershed zones, which are areas that are supplied by the distal branches of two different major arteries. Commonly affected areas in the colon: splenic flexure and rectosigmoid junction

Question 59

Why can pregnant women develop supine hypotension syndrome?

Answer 59

Patients at >20 weeks gestation experience compression of the inferior vena cava by the gravid uterus while in the supine or right lateral decubitus position. Without substantial collateral blood flow, the consequent reduction in venous return and cardiac output can cause severe hypotension (supine hypotension syndrome)

Question 60

What is rocky mountain spotted fever and the treatment?

Answer 60

Rocky mountain spotted fever is a tick borne illness due to Rickettsia rickettsii, a weakly gram-negative, obligate intracellular organism that has an affinity for vascular endothelial cells. Patients usually have nonspecific symptoms (fever, malaise, myalgia) followed by a macular-petechial rash that beings on the ankles and wrists and spreads to the center of the body as well as to the palms and soles. Urgent treatment with doxycyline, an inhibitor of bacterial protein synthesis, is required

Question 61

What is strongyloides stercoralis?

Answer 61

transmitted in tropical/subtropical climates when human skin comes into direct contact with filariform larvae. The larvae penetrate the skin, enter the bloodstream, pass through the lungs, and are swallowed into the digestive system. Common manifestation include linear skin rash and irritative digestive/respiratory symptoms

Question 62

Traits of enterococcus

Answer 62

Enterococcus is a component of the normal colonic and urogenital flora and is capable of growing in hypertonic saline and bile. It is gamma-hemolytic, catalase-negative, and pyrrolidonyl arylamidase positive. Genitourinary instrumentation or catheterization has been associated with enterococcal endocarditis

Question 63

What are the major defects in tetralogy of Fallot?

Answer 63

Right ventricular outflow tract obstruction and ventricular septal defect. Cyanotic ("tet") episodes are commonly precipitated by a dynamic rise in RVOT obstruction that increases right to left shunting through the VSD. These episodes involve decreased blood flow through the RVOT, causing disappearance of the associated systolic murmur and reduced oxygen saturation of left ventricular blood.

Question 64

What obesity hypoventilation syndrome?

Answer 64

commonly presents with chronic fatigue, dyspnea, and difficulty concentrating. Patients will have BMI>30 and arterial blood gas while awake showing evidence of hypoventilation, including hypercapnia (PaCO2 >45) and usually hypoxemia (PaO2 (75). The expected alveolar to arterial oxygen gradient is normal (4-15) with hypoventilation

Question 65

What is a study's power?

Answer 65

A study's power increases as its sample size increases. Therefore, the larger the sample, the greater the ability of a study to detect a difference when one truly exists.

Question 66

The pressure tracing for aortic regurgitation is characterized by?

Answer 66

Aortic regurgitation causes a decrescendo diastolic murmur with maximal intensity occuring just after closure of the aortic valve, when the pressure gradient between the aorta and left ventricle is the highest. The pressure tracing for aortic regurgitation is characterized by the loss of the aortic dicrotic notch, steep diastolic decline in aortic pressure, and high-peaking systolic pressures.

Question 67

The suprachiasmatic nucleus regulates?

Answer 67

circadian rhythm by processing light clues in the environment to modulate alertness, body temp, and production of hormones (cortisol, melatonin). Dyssynchrony between the local environment (daylight hours, work schedules) and internal circadian rhythm can cause insomnia and daytime sleepiness (jet jag)

Question 68

Most of the cutaneous lymph from the umbilicus down, including the anus below the dentate line, drains to?

Answer 68

the superficial inguinal lymph nodes. Exceptions are the glans penis and posterior calf, which drain to the deep inguinal nodes

Question 69

How does alcohols work to disinfect?

Answer 69

Alcohols function by disorganizing the lipid structure in membranes, causing them to be leaky, and by denaturing cellular proteins. They are bactericidal, tuberculocidal, fungicidal, and virucidal, but do not destroy bacterial spores.

Question 70

What provides innervation to the ear canal?

Answer 70

The vagus nerve provides cutaneous sensation to the posterior external auditory canal via its small auricular branch. Sensation of the rest of the canal is from the mandibular division of the trigeminal nerve.

Question 71

Why is obesity a common risk factor for endometrial cancer?

Answer 71

Endometrial hyperplasia and cancer often present with postmenopausal bleeding. A common risk factor for endometrial cancer is obesity due to the peripheral aromatization of androgens to estrogens in adipose tissue, which leads to chronic unopposed estrogen exposure and uncontrolled endometrial tissue proliferation.

Question 72

MOA of proton pump inhibitors?

Answer 72

Management of GERD includes lifestyle and dietary modifications (weight loss, tobacco avoidance) and meds such as PPIs (pantoprazole, omeprazole) or histamine 2 receptor antagonists (famotidine). PPIs irreversibly inhibit the H/K ATPase on parietal cells, which decreases gastric acid secretion.

Question 73

Cytokeratin is a immunohistochemical marker for?

Answer 73

epithelial cell carcinomas

Question 74

What does the HER2 oncogene encode for?

Answer 74

Encodes for a transmembrane glycoprotein with intrinsic tyrosine kinase activity and is a member of the gamily of epidermal growth factor receptors. Overexpression of this protein is associated with a worse prognosis and increased risk of disease recurrence.

Question 75

What kills people after a lighting injury?

Answer 75

Although lightning injuries are rare, they are associated with a 25% fatality rate. Two-thirds of lightning-related deaths occur within the first hour after injury, with fatal arrhythmias and respiratory failure as the most common causes. Patients with minor cutaneous involvement may still have major internal injury after lightning strikes and high voltage electrical contact.

Question 76

What is a pheochromocytoma?

Answer 76

a malignancy arising from chromaffin cells of the adrenal medulla that typically presents with episodic headaches, diaphoresis, and hypertension.

Question 77

The adrenal medulla is derived from?

Answer 77

neural crest cells (multipotent, migratory cells that originate in the ectoderm), which also give rise to melanocytes and neural ganglia.

Question 78

What is a life threatening complication of fibrinolytic therapy?

Answer 78

Fibrinolytic therapy for acute ST-segment elevation myocardial infarction improves clinical outcomes when percutaneous coronary intervention is unavailable. A life threatening complication of fibrolytic therapy is intracerebral hemorrhage, which should be suspected in a patient with acute neurologic deterioration

Question 79

What is serum sickness?

Answer 79

an immune complex mediated, type III HSR that occurs when immune complexes deposit in skin and joints and activate the classical complement cascade. This generates the highly inflammatory anaphylatoxins C3a and C5a, leading to skin rash, joint arthralgia/arthritis, and high fever.

Question 80

What is aldolase B deficiency (hereditary fructose intolerance)

Answer 80

leads to accumulation of the toxic metabolite fructose-1-phosphate. Patients have hypoglycemia and vomiting when fructose or sucrose is consumed. Treatment involves strict removal of both carbohydrates from the diet.

Question 81

What is a lead-time bias?

Answer 81

occurs when a new test diagnoses a condition earlier than conventional studies, causing an apparent increase in survival time despite no improvement in overall mortality. Long term mortality rates, not survival times, should be considered for measuring the effect of early screening and treatment.

Question 82

What is cutaneous leishmaniasis?

Answer 82

Leishmania species are obligate intracellular protozoa that mature in macrophages and can be identified on biopsy by the presence of rod-shaped kinetoplasts. They are transmitted to humans by infected sand flies and cause the clinical syndrome of cutaneous leishmaniasis, characterized by a chronic, pinkish papule that evolves into a nodule or plaque.

Question 83

Control of Mycobacterium tuberculosis infection is mediated primarily by?

Answer 83

activated macrophages, which surround extracellular mycobacteria and wall them off within granulomas. The release of digestive enzymes by these cells not only helps control the infection, but also leads to damage of the surrounding tissue and the formation of cavitary lung lesions.

Question 84

What is the virulence factor for Bacillus antracis?

Answer 84

Bacillus anthracis is a large, sporulating, gram+ rod that is encased in an antiphagocytic polypeptide capsule composed of D-glutamic acid. Inhalation of B anthracis spores can cause pulmonary anthrax, which is usually characterized by nonspecific symptoms followed by hemorrhagic mediastinitis, shock, and death.

Question 85

How does prone positioning improve arterial oxygenation in patients with severe acute respiratory distress syndrome?

Answer 85

Results from reduced compression of the posterior lung segments, where the majority of alveoli are located. This leads to more evenly distributed ventilation throughout the lungs with reduced intrapulmonary shunting and improved ventilation-perfusion matching

Question 86

What is the most common cause of aortic stenosis in developed countries, typically affecting patients age >70?

Answer 86

Age related calcific degeneration of a normal trileaflet aortic valve. Aortic stenosis is recognized by a crescendo-descrendo murmur best heard at the right upper sternal border with radiation to the carotid arteries. When severe, it causes symptoms (eg, dyspnea on exertion, presyncope) due to resriction of cardiac output.

Question 87

Pancreatic neuroendocrine tumors stain positive for?

Answer 87

Functional (eg, insulinoma, gastrinoma, glucagonoma, VIPoma) and nonfunctional pancreatic neuroendocrine tumors are histologically characterized by uniform tumor cells with an organoid architecture (eg, nested, glandular, ribbon, or pseudorosette arrangement). The cells have characteristic salt and pepper chromatin, as well as granular cytoplasm, and stain positive for synaptophysin and chromogranin A.

Question 88

Amyloid can deposit in the brain in which disease?

Answer 88

Amyloid is an abnormally folded (insoluble) extracellular protein that has apple-green birefringence when stained with Congo red and viewed under polarized light. Alzheimer disease is associated with beta-amyloid deposits in the brain parenchyma (neuritic plaques) and walls of cerebral vessels (amyloid angiopathy)

Question 89

As a class, second generation antipsychotics are associated with?

Answer 89

metabolic adverse effects (eg, weight gain, dyslipidemia, hyperglycemia, increased risk of diabetes). Within the class, olanzapine and clozapine carry the greatest risk.

Question 90

Why can constipation occur in pregnancy?

Answer 90

Constipation is common during pregnancy and results from the inhibitory effect of progesterone on colonic smooth muscle contractions and the fasting migrating myoelectric complex. Other common pregnancy-related changes of the GI system include decreased lower esophageal sphincter pressure (leading to gastroesophageal reflux) and gallbladder stasis (leading to gallstone formation)

Question 91

MOA of celecoxib

Answer 91

Cyclooxygenase-2 (COX-2) is an inducible enzyme upregulated during inflammation by IL-1 and TNF-alpha. Selective COX-2 inhibitors (celecoxib) decrease inflammation by inhibiting COX-2 production of pro-inflammatory arachidonic acid metabolites. Because they do not affect COX-1, they have minimal gastroduodenal toxicity.

Question 92

For a purified RNA molecule to induce viral protein synthesis in a host cell, it must be able to?

Answer 92

act directly as mRNA using the host's intracellular machinery for translation. Therefore, in general, purified single stranded positive sense RNA can be infectious; single stranded negative sense or double stranded RNA is not.

Question 93

Abducens nerve innervated which eye muscle?

Answer 93

The abducens nerve (CN VI) innervated the lateral rectus muscle, which originates at the annular tendon and inserts on the temporal (ie, lateral) surface of the globe. It functions to abduct the eye.

Question 94

What is status epilepticus?

Answer 94

a single seizure lasting >5 minutes or the occurrence of multiple discrete seizures with incomplete recovery of consciousness between episodes. The initial treatment includes intravenous lorazepam and phenytoin given concurrently.

Question 95

MOA of phenytoin

Answer 95

a long acting anticonvulsant that inhibits neuronal high frequency firing by reducing the ability of sodium channels to recover from inactivation.

Question 96

The middle meningeal artery is a branch of?

Answer 96

the maxillary artery, which enters the skull at the foramen spinosum and courses intracranially deep to the pterion (where the frontal, parietal, temporal, and sphenoid bones meet) Skull fractures at this site may cause laceration of this vessel, leading to an epidural hematoma.

Question 97

Sunlight exposure catalyzes conversion of what in the skin?

Answer 97

catalyzes conversion of 7-dehydrocholesterol to cholecalciferol (vitamin D3) in the skin. Subsequent 25-hydroxylation in the liver and 1-hydroxylation in the kidneys produce 1,25-dihydroxyvitamin D, the active form. Inadequate exposure to sunlight can lead to vitamin D deficiency.

Question 98

How does testicular torsion present?

Answer 98

presents with acute, severe, progressive unilateral scrotal pain. Classic examination findings include scrotal edema and discoloration, a high riding testicle and an absent cremasteric reflex (ie, absence of testicular elevation when stroking the ipsilateral thigh)

Question 99

What is neutropenic fever?

Answer 99

Patients wit neutropenic fever (ie, temp >101 F and absolute neutrophil count <500) are at risk for overwhelming bacterial infections. The majority of severe infections that cause rapid clinical deterioration (eg, 4 hours) are caused by gram-negative organisms that produce endotoxins

Question 100

What are the neuropathologic features of Alzheimer?

Answer 100

neurodegeneration, amyloid plaques (ie, extracellular accumulation of beta amyloid), and neurofibrillary tangles. Neurofibrillary tangles are formed when tau, a protein associated with neuronal microtubules, becomes hyperphosphorylated and disassociated from the microtubules to form paired helical filaments

Question 101

What is wobble?

Answer 101

The first two nucleotide positions on an mRNA codon require traditional (Watson-Crick) base pairing, whereas the third nucleotide position may undergo less stringent wobble pairing. This allows one tRNA molecule to recognize different codons that code for the same amino acid.

Question 102

Patients with undescended testicles are at increased risk for?

Answer 102

infertility (due to atrophy of temperature sensitive Sertoli cells) and testicular germ cell tumors (eg, seminoma). Orchiopexy (surgical fixation of the testis in the scrotum) decreases, but does not eliminate, these risks.

Question 103

What is used in a Southwestern blot?

Answer 103

Double straned DNA probes are used in the southwestern blot technique to identify DNA binding proteins, including transcription factors such as nuclear factor kappa B

Question 104

What is high altitude illness?

Answer 104

People traveling to elevations >2500 m (8000 ft) can develop high altitude illness, characterized by hypobaric hypoxia with the potential to develop life threatening cerebral and/or pulmonary edema. Key adaptive responses to hypoxemia include hyperventilation to increase blood oxygenation and increase synthesis of 2,3 bisphosphoglycerate in erythrocytes (facilitating oxygen offloading into peripheral tissues)