1- (D) doesnt enjoy being with people, prefers individual activities, indifferent to sexual intimacy --> Schizoid 2- (F) Uterosacral Ligament is the only structure that extends posteriorly 3- (D) young female, neurological symptoms, white matter plaques --> Multiple Sclerosis 4- (D) Local IL-1 and TNF effects lead to activation of osteoclasts and bone resorption--> hypercalcemia 5- (E) Ischemia stimulates baroreceptors in afferent arterioles--> increased renin 6- (F) Cocaine works by inhibiting NE reuptake at the presynaptic terminals 7- (D) Post partum hemorrhage, placenta adherent to the uterus, no decidua--> Placenta accrete 8- (D) NE acts on B1 receptors in the SA node, AV node and cardiac myocytes to increase rate and contractility 9- (C) Chronic mal-absorption leading to signs of severe vitamin deficiencies (retinal degeneration, ataxia, motor dysfunction) + acanthocytosis + low cholesterol--> abetalipoproteinemia due to Apo B 100 deficiency 10- (C) Exposure to paint thinner + ophthalmologic and neurologic symptoms + anion gap metabolic acidosis--> probably methanol exposure which is metabolized by Formaldehyde dehydrogenase 11- (F) Parasympathetic innervation to the stomach provided by the vagal trunks increases acid output; other choices are all sympathetic 12- (C) Inheritance passed by female to 100% of offspring--> mitochondrial; variation in symptoms explained by Heteroplasmy 13- (D) CRF in middle age + family history + bilateral abdominal masses--> Polycystic kidney disease 14- (A) Long-term heavy smoker, painless hematuria--> most probably Bladder Cancer 15- (B) Abdominal pain, nausea, vomiting short time after eating pastries + no fever--> Enterotoxin ingestion 16- (C) Chronic transplant rejection carried out by CD8+ T cells is due to Direct cytotoxicity to graft cells 17- (B) Withdrawal symptoms of Heroin include hyper-excitability and increased sympathetic discharge 18- (A) History of hypercoagulability and miscarriage + prolonged PTT--> Antiphospholipid antibody syndrome 19- (B) Interferon-y receptor deficiency leads to defective intracellular killing of mycobacteria by macrophages 20- (F) All symptoms suggestive of scleroderma which leads esophageal fibrosis--> decreased peristalsis and LES tone. 21- 22- (H) HSV becomes protected from immune response by establishing a latent infection in the sensory nerve cells, in case of genital herpes in the dorsal root ganglia of the lumbar or sacral plexus. 23- (E) The most common cardiac tumor in adults, in addition to being a famous source of embolism is myxoma, usually in the left atrium 24- (A) The clinical picture is suggestive of tetanus poisoning due to wound infection by clostridium tetani, the toxin works by inhibiting the release of the inhibitory neurotransmitter glycine in the spinal cord leading to disinhibition of the motor nerve cells 25- (A) The clinical picture is suggestive of Cushing disease due to increased ACTH secretion by pituitary adenoma leading to hyperplasia of the cells in the zona fasciculata of the adrenal glands 26- (A) The antibody worked by blocking the tumor receptor on the surface of hepatocytes, preventing tumor cells from homing to the liver cells 27- (D) Absence of blinding in the study created an observer bias which led to variability in outcome assessment 28- (C) The patient is clearly affected by the severity of his pain, he hasnt attempted suicide on his own so I think restraining him wouldnt be of benefit, reevaluating him after controlling the precipitating factor (i.e. the pain) would be the best option 29- (D) The patients behavior is strongly related to instances in which she becomes separated from her mother which can be considered normal behavior only between 12-18 months of age, in addition no signs of defiant or criminal behavior to justify oppositional defiant or conduct disorders, respectively. 30- (E) Variation in phenotype between individuals carrying the same genotype defines variable expressivity 31- (E) Acetazolamide acts by inhibiting bicarbonate reabsorption and hydrogen ion secretion in the proximal tubule 32- (E) The photograph shows a collection of blood vessels of abnormal shape in the medial side of the brain, together with the history of seizures this is suggestive of congenital vascular malformation 33- (D) History of amenorrhea and infertility + obesity + hirsutism--> polycystic ovarian syndrome 34- (A) Micafungin, like capsofungin, works by inhibiting carbohydrate synthesis in the fungal cell wall 35- (B) The patients diet rules out dietary deficiency as a cause, besides there is a high incidence of other autoimmune disorders in patients who have autoimmune thyroiditis, among those is pernicious anemia 36- (A) Ligaments, like cartilage are avascular and therefore lack of good blood supply would slow down the healing process 37- 38- (D) History and symptoms are suggestive of heart failure, the presence of lowered PO2 indicates respiratory insufficiency which in case of heart failure is commonly caused by pulmonary edema 39- (A) The presence of alveolar hyaline membranes is indicative of ARDS which is the only acute process involving diffuse alveolar damage, the other choices all indicate a chronic process 40- (D) The HSG shows a malformed unicornuate uterus which is caused by the dysgenesis of the paramesonephric ducts 41- (A) The lab findings show hyponatremia and decreased plasma osmolality and increased urine osmolality indicative of hypersecretion of ADH 42- (C) Warfarin causes a decrease in factors II, VII, IX, and X, its toxicity can be treated by vit. K in mild cases and fresh frozen plasma in severe cases 43- (C) The photo shows gram positive bacilli, the only one from the choices thats fits the description is Listeria 44- (C) Left sided numbness and paralysis that are more severe in the face and upper limb--> middle cerebral artery infarction 45- (D) Since the neurovascular bundle runs in the lower part of the rib all the choices with below can be ruled out. The only left choice thats below 7th rib is (D). In addition thoracentesis should be done between 8th and 10th ribs to avoid lung injury 46- (A) The presence of adhesins (pilli) aids the bacteria in adhering to the urinary tract epithelium and withstanding the urine flow 47- (D) LD= Vd X Css= 8 X 0.35= 2.8 mg/kg X 55 kg = 154 mg 48- (C) The most beneficial drug in hepatic encephalopathy is lactulose, works by trapping ammonium in the intestines. 49- 50- (F) The case indicates nephrogenic DI, the proximal tubule is always isotonic. The ADH works on the distal tubule and collecting ducts, when its action is blocked the osmolality inside these regions will be hypotonic Block 2: 1- (D) Cephalexin like all other b-lactams works by inhibiting bacterial cell wall synthesis 2- (A) Hypoglycemia triggers glucagon release which activates adenylyl cyclase in the liver leading to glycogen breakdown 3- (B) Hereditary hemochromatosis is caused by increased absorption of iron from the small intestine 4- (A) History indicating a case of pulmonary embolism, in which perfusion is cut while ventilation remains normal 5- (B) Cisplatin works by cross-linking DNA 6- (C) Tachycardia and hypotension + the other symptoms are suggestive of ongoing hemorrhage, the presence of weak pulse in lower limbs makes leaking aortic aneurysm the most probable answer 7- 8- (B) Winging of the scapula after mastectomy--> long thoracic nerve injury 9- (C) Typical case of multiple myeloma 10- (A) Unilateral headache and tearing and rhinorrhea + symptoms occur regularly every day at the same time and at same period over years --> cluster headache 11- (A) The description typically fits apoptosis, the man probably was suffering from acute viral hepatitis 12- (C) The womans history is suggestive of atherosclerosis which is a risk factor for ischemic colitis, in addition the splenic flexure is a watershed area between the middle and left colic arteries and is most commonly affected in cases of ischemic colitis 13- (C) Homologous pairing is essential for crossing over, in which homologous chromosomes exchange segments with each other during meiosis 1, this is necessary for genetic variation 14- (B) Typical case of Goodpastures syndrome in which antibodies attack basement membranes, causing crescentric glomerulonephritis with linear immunoflourescence and alveolar damage 15- (D) Old age, left lower quadrant pain, fever + typical CT scan findings--> diverticulitis 16- (E) Since the antigen was a polysaccharide it generated only a B cell response which led to only IgM production. IgG response requires isotype switching from IgM which depends on T cell stimulation to B cells, T cells in that case were not stimulated because they recognize only protein antigens not polysaccharides. 17- (B) The reason for increased risk of gastric adenocarcinoma in the Japanese population is the carcinogens present in the diet, the patient continued consuming the same diet after his arrival. 18- (C) Overdosage of neostigmine caused desensitization of the nicotinic receptors at the motor end plate. MG is due to autoimmune deactivation of nicotinic receptors, so choice A and other choices involving muscarinic receptors can be ruled out. 19- (D) Hand cleansing is generally the most important and effective measure in preventing nosocomial infections, not sure however about choice (B), someone else should confirm 20- (E) Praziquantel is the only choice that works by the way described in the question stem 21- (B) Elbow flexion is done mainly by the biceps and brachialis muscles, both supplied by the musculocutaneous nerve. 22- (D) Imprinting in that case caused Prader-Willi syndrome because he inherited the defective chromosome from his father, while his cousin has Angelman syndrome because she inherited that chromosome from her mother. 23- (E) As the stimulation frequency increases the amount of calcium released from the sarcoplasmic reticulum increases, and so the amount of calcium sequestered in order to be able to release a greater amount of calcium with each successive contraction. 24- (D) The results show that those who have a high selenium diet have 0.3 the risk of those who have a diet low in selenium (i.e. a lower risk), and since the CI doesnt contain 1 the result can be considered significant. 25- (D) Premature baby with respiratory distress + typical findings on CXR--> neonatal RDS due to surfactant deficiency. 26- (E) Thats the function of myeloperoxidase; converting hydrogen peroxide into hyalide radicals 27- (B) Using compression sleeves is one of the recommended treatments for lymphedema http://en.wikipedia.org/wiki/Lymphedema#Compression 28- (C) The lab results show severe anemia with normal MCV (so its neither iron nor B12 deficiency), they also show high creatinine and BUN (consistent with Hx of DM) so the most probable cause of the anemia is chronic renal failure 29- (D) The history suggests minimal change nephropathy, a disease characterized by heavy selective proteinuria due to loss of negative charge in the glomerular basement membrane 30- 31- (F) Slow nerve conduction indicates a problem in the myelin sheath, leading to slowing down of action potential propagation; the latter depends on voltage gated Na channels. Neurotransmitter gated channels serve to make the initial excitation to the nerve, so their impairment would lead to absent impulse not slowed conduction. 32- (B) Tough one! Quote: The first step in population sampling is identifying the population which the researchers wish to learn more about. If, for example, someone wants to find out how many African Americans have cats, the researchers know that the population under scrutiny is the African American community. Population sampling is used to select representative individuals from this vast community so that an estimate about cat ownership among other members of this community can be extrapolated. On the other hand convenience sampling is the one in which a sample of readily accessible individuals is used, rather than a diverse sample of larger population. This link explains it all http://www.wisegeek.com/what-is-a-population-sampling.htm 33- (D) Classical example and photo of subarachnoid hemorrhage 34- (B) Tachycardia, hypertension, papillary dilatation and diaphoresis all point out to increased sympathetic discharge typical of amphetamine and cocaine intoxication 35- (D) Hemidesmosomes anchor basal cells of the epidermis to the basement membrane; the case described is a case of bullous pemphigoid. Desmosomes on the other hand serve to attach the cells of the epidermis to each other not to BM, and they are destroyed in pemphigus vulgaris. 36- (E) The man most probably has immotile cilia syndrome which is characterized by sinusitis, bronchiectasis, immotile sperms, and usually situs inversus totalis. 37- (D) The description typically fits pheochromocytoma, when such a tumor occurs outside the adrenal gland, it is called paraganglioma. 38- (B) The organism described is pseudomonas aeroginosa, normally it is not encapsulated, but in cystic fibrosis the organism produces a capsule of sodium alginate that forms a biofilm around the organism and makes it difficult for antibiotics to penetrate. 39- (E) Typical description of pneumocytes type II that produce surfactant. 40- (E) History of hypovolemia and urine analysis shows: granular cast, oliguria, increased sodium excretion (>1%), and fixed osmolality. All points to acute tubular necrosis which is a reversible condition; upon restoration of normal blood volume, the tubular cells regenerate. 41- (C) The pulmonary circulation originates from the right ventricle and receives all of the cardiac output; the bronchial circulation on the other hand originates from left ventricle and is part of the systemic circulation and so receives only a part of the cardiac output. 42- (C) History of amenorrhea for two months without any associated symptom or sign puts pregnancy on top of the list; best thing to rule it out is doing serum B-HCG. 43- (A) The only open-ended question, the others jump to assumptions and in addition all contain closed-ended questions. 44- 45- (E) Ubiquitination of the misfolded proteins (tagging them with ubiquitin protein) is the signal for the proteasome to attack these misfolded proteins. 46- (F) Testosterone is the only choice of which decreased concentration would lead to erectile dysfunction. 47- (D) A case of disuse atrophy in which there is increased protein degradation in the muscle cells leading to decrease in their size, but they dont die, it is a reversible a condition. 48- 49- (E) Induction of cytochrome P450 by alcohol leads to increased metabolism of acetaminophen by this enzyme, which leads to increased production of hepatotoxic metabolites. This is how alcohol lowers the threshold for acetaminophen toxicity. 50- (B) Treatment of infertility of unapparent cause often starts with a trial to increase the ovulation in order to increase the probability of fertilization; the drug most commonly used to induce ovulation is clomiphine citrate. block 31- (D) The question is referring to Neisseria gonorrhea, one of its most important virulence factors is the pilli (fimbria) with which it can adhere to the urinary tract epithelium 2- (A) Tretinoin is a form of vitamin A, as other fat soluble vitamins it works by binding to intracellular receptor to activate nuclear gene transcription 3- (C) In patients who have aspirin induced asthma the aspirin triggers the attack by inhibiting the production of prostaglandins from arachidonic acid by cyclooxeganse, shifting all arachidonic acid to be converted to leukotrienes by the enzyme lipooxygenase; which in turn causes bronchoconstriction 4- (E) IL-2 produced by stimulated CD4+ T cells works on the interleukin receptor on other T lymphocytes to stimulate their proliferation 5- (D) History of dementia + gait and urinary problems + enlarged ventricles--> most probably normal pressure hydrocephalus 6- (A) Atropine is the best initial treatment for organophosphorus poisoning 7- (A) B-chains are characterized by their ability to bind 2,3 bisphosphoglycerate, which in turn decreases its affinity to oxygen, this is the reason why Hb A has lesser affinity to O2 compared to Hb F whose y-chains cant bind to that substance 8- (F) Being HIV positive and with the acute presentation + plus the interstitial infiltrate and the silver stained specimen make PCP pneumonia the most probable answer 9- (B) Most probably the allele of P53 linked to the m allele of the locus is defective (i.e. the normal cells have are heterozygous; they have only one normal allele which is the one linked with the n allele of the locus). The tumor cells have lost this single normal allele, so in these cells both alleles are now defective 10- (E) Diarrhea not improved with fasting = secretory diarrhea, so this eliminates all the choices but cholera and VIP, hypokalemia and hyperglycemia in addition to the absence of travel history makes VIP the most probable answer 11- (C) History of recurrent UTI + the description of a calculus filling the renal pelvis is consistent with staghorn calculus thats formed from magnesium ammonium phosphate (also called struvite) 12- (B) Ischemia in the heart leads to coagulative necrosis 13- (D) In case of congestive heart failure the atrial myocytes secrete atrial natriuretic peptide (ANP) that inhibits Na reabsorption, increased Na delivery to the macula densa leads to inhibition of renin release 14- (A) HLA-B27 (a subclass of MHC class 1) shows the strongest assossiation with ankylosing spondylitis 15- (D) Alcoholism selectively destroys the vermis (central) part of the cerebellum which is responsible for coordination of truncal movements, leading to gait instability. The other choices are fine movements coordinated by the more lateral parts of the cerebellum 16- (D) A case of congenital hypertrophic pyloric stenosis 17- (B) Ciprofloxacin like other flouroquinolones works by inhibiting DNA gyrase, bacteria resistant to that class of drug have an enzyme thats not affected by it 18- (E) Mild GERD can be treated by diet and lifestyle modifications, in addition to antacids or a protective agent as sucralfate, no need for acid suppression. 19- (C) The case describes infection with diphtheria, the toxin works by ADP ribosylation of elongation factor-2 20- (B) Informed consent entails that the patient be fully informed about the purpose, methods, benefits, risks and alternatives of any procedure performed 21- (C) Nitric oxide (NO) is used as a vasodilator to treat pulmonary hypertension; nitroglycerin is a famous precursor to nitric oxide. It is an oxidizing agent that can lead to the oxidation of iron inside the hemoglobin converting it to methemoglobin and rendering it incapable of binding to oxygen. 22- (B) Collapse of the femoral head with preservation of the cartilage indicates avascular (aka aseptic) necrosis; the cartilage being an avascular structure is protected from the effects of ischemia, while the femoral head is highly vulnerable to ischemia due to its limited blood supply. The corticosteroids taken by the patient is a known risk factor for aseptic necrosis of the femur. 23- (A) The rash is due to the late phase of type I hypersensitivity in which eosinophils arrive to the scene as a result of the chemotactic factors released by mast cells in addition to histamine during the early phase 24- (F) Uterine relaxation (tocolysis) is the only choice thats mediated by B2 adrenoreceptors. 25- (C) Bupivacaine, like most other local anesthetics, works by inhibiting membrane Na channels and so decreasing the excitability of the sensory nerves. 26- (E) The case is probably cretinism. The remnant that would be expected to form a midline cyst in such a case is the thyroglossal duct. 27- (C) The photo shows the desmoplastic reaction characteristic of ductal carcinoma; the most important prognostic factor is the degree of spread (staging) of the tumor. 28- (A) The only choice that characterizes hypochondriasis. Somatoform patients are usually indifferent to their disease (la belle indifference). 29- (C) The only drug of the choices that would cause steatorrhea is orlistat, because it works by inhibiting fat digestion and absorption in the small intestine by inhibiting pancreatic lipase. 30- (C) Smoking causes squamous metaplasia of the respiratory epithelium present in the larynx, trachea and bronchi. The metaplastic epithelium is a risk factor for squamous cell carcinoma 31- (C) Out of the 200 people who ate lettuce, 40 developed diarrhea. The probability of developing diarrhea is 40/200=0.2 32- (A) The thoracic portion of the esophagus takes blood supply from branches of the aorta and the bronchial arteries. 33- (B) The clinical picture indicates impairment of function of the mitochondria inside heart cells. Since the mutation affects tRNA, protein synthesis would most likely be impaired. 34- (B) Pyelonephritis is the most probable complication in that case with a history of recurrent UTI, leukocytosis and bilateral hydroureter and hydronephrosis. 35- (G) All the symptoms, signs and lab results are typical of hypothyroidism. The most accurate initial test is serum TSH. 36- (B) The number one cause of death of both men and women in developed countries is cardiovascular disease, followed by cerebral infarction, followed by cancer. 37- (B) The patient most probably has celiac disease (malabsorption syndrome controlled by restricting wheat, barley and rye). The pruritic vesicular rash on the elbows associated with celiac disease is called dermatitis herpetiformis. 38- (C) History typical of Lesch-Nyhan (self-mutilating behavior, neurological symptoms and x-linked inheritance). It is caused by HGPRT enzyme deficiency leading to hyperuricemia. 39- (E) Observing a group of patients who have the risk factors of a disease for the occurrence of that disease describes prospective cohort study. 40- (C) Glossitis, angular stomatitis and especially spoon-shaped nails are found in iron deficiency anemia, also it is the only cause among the choices for decreased MCV. 41- (A) A crescendo-decrescendo systolic murmur thats best heard in the second right intercostal space and radiates to the carotids--> aortic stenosis 42- (D) The history is typical for Duchennes muscular dystrophy (x-linked, delayed milestones, positive Gowers sing), the muscle described is the adductor magnus which takes origin partially from the inferior ramus of the ischium, and inserts into the medial side of the femur. 43- (E) The case describes oculomotor nerve palsy (mydriasis, ptosis and outward strabismus), the only muscle of the choices thats not supplied by CN III is the superior oblique (CN IV) 44- (B) The only statement that doesnt direct the patient or judge him, nor try to threaten and intimidate him. 45- (E) The only conscious defense mechanism that can be learned and would be beneficial in that case is suppressions of the memory of his father. 46- (E) The ureters are crossed by the ovarian vessels and are liable to accidental ligation during oophorectomy; the flank pain is consistent with the urinary retention that would result from ligation of the ureter. 47- (B) The two drugs that act as cough suppressants are codeine and dextromethorphan. Compared to codeine, dextromethorphan is a less potent opiate, it has a much less abuse potential and doesnt cause constipation. 48- (C) The case describes Chediak-Higashi syndrome, an immunodeficiency syndrome due to defective neutrophil function due to failure of phagolysosome formation. 49- (B) Neuraminidases are enzymes that clip off the terminal sialic acid residues from the newly formed virions in order for them to be released from the cell membrane of the infected cells. 50- (A) The case describes acute intermittent porphyria, which is autosomal dominant. Except for congenital erythropoietic porphyria (AR), all the other well known types of porphyria are AD.Block 4 1- (E) EBV infects B-lymphocytes, but the cells that react to the infection are T-lymphocytes because it is a viral infection. In EBV infection the reactive T cells undergo some morphologic changes (become enlarged with abundant vacuolated cytoplasm) and are called atypical lymphocytes. 2- (E) Erythromycin, like other macrolides, works by inhibiting translocation of the ribosome along the mRNA. Choice B is puromycin, C is diphtheria toxin, and D is tetracyclines. 3- (B) Hemangioma is a benign tumor that arises from the endothelial cells that line the blood vessels. 4- (E) Sumatriptan activates 5HT1B/1D receptors, which are serotonin receptors. 5- (C) Positive predictive value (PPV) equals (TP/TP+FP), when the prevalence increases, the rate of the false positive (FP) decreases and so the PPV increases. 6- (B) Hyperreflexia (sign of UMN lesion) + fasciculations (sign of LMN lesion) indicate most probably a case of amyotrophic lateral sclerosis (ALS). It is characterized by difficulty swallowing due to paralysis of the somatic muscles of the pharynx and upper esophagus. 7- (C) Staphylococcus aureus most probably caused the acute endocarditis in much the same way it causes it in IV drug abusers; by getting access from skin wound into the right side of the heart. 8- (J) Typical description of VSD. 9- (D) A case of ovarian torsion, which causes obstruction of the ovarian blood vessels that pass through the suspensory ligament of the ovary leading to ovarian ischemia. 10- (C) Most probably a case of Giardia lamblia, the diagnosis can be made by visualizing ova and parasites in the stool 11- (A) Bevacizumab is a humanized monoclonal antibody directed against VEGF, it comes from human origin using recombinant DNA technology, and thus it doesnt encounter a strong immune response against them, unlike antibodies extracted from other species that encounter a strong immune response leading in many cases to type III hypersensitivity reactions (serum sickness) 12- (A) The patient most likely has a prolactin secreting pituitary adenoma, the treatment is with a dopamine agonist (like bromocriptine of cabergoline) that inhibits prolactin production and in the majority of patients leads to shrinkage of tumor size. 13- (C) The photograph shows the neuromuscular junction, Lambert-Eaton syndrome is an autoimmune disorder caused by production of Abs against the presynaptic calcium channels at the NMJ, leading to inhibition of Ach release; it usually involves the proximal muscles especially of the lower limbs, and is associated with cancer. 14- (C) HPV E6 protein is the only foreign protein shown, and thus it would produce the strongest immune response, all the other proteins are self-proteins. 15- (E) These symptoms are suggestive of carcinoid syndrome caused by metastatic carcinoid tumor; the most common primary site for this tumor is the appendix followed by the small intestine. 16- (A) The stem describes a branchial cyst, formed due to incomplete obliteration of the second branchial cleft by the branchial arch during embryonic development; it is found in front of the anterior border of the sternomastoid muscle. (N.B. The other cystic neck swelling, cystic hygroma, is found along the posterior border). 17- (C) The most plausible answer is inhibition of CYP450, but I cant come up with a good explanation for it. 18- (C) Having an affected child with an AR disease means that both parents are carriers, so the probability the next child is 50% being carrier, 25% being homozygous normal, and 25% being affected with the 2 recessive alleles. 19- (D) The case describes mucopolysaccharidosis (specifically Hunters syndrome) thats X-linked and is characterized by the deficiency of iduronate sulfatase enzyme that metabolizes mucopolysaccharides as heparan and dermatan sulfate. 20- (F) One of the most serious side effects of metformin is lactic acidosis, due to inhibition of aerobic metabolism in muscles. 21- (D) The case describes mitochondrial myopathy in which ragged-red fibers is a characteristic finding. The most important mitochondrial process that becomes impaired in these patients is oxidative phosphorylation, and this impairment is the cause of elevated lactic acid. 22- (E) The use of gentamicin (nephrotoxic drug), high urinary Na level (>20 mEq/L) and the presence of brown granular cast all suggest a case of ATN which mostly affects the PCT because it is the most metabolically active and energy demanding part of the kidney. 23- (A) Since the patient is borderline obese, the most important recommendation would be to lower his weight. A low calorie diet that takes into account all types of food taken is more efficient than targeting any single category. 24- (E) High carboxyhemoglobin indicates CO poisoning, CO impairs oxidative phosphorylation in the mitochondria by inhibiting the last step catalyzed by the enzyme cytochrome oxidase (aka Cyt a+a3) 25- (A) In cases of acute inflammation such as this one (acute appendicitis) certain cytokines released from the PMNs and macrophages in the inflammation site act on the hypothalamus to produce fever, the most important of these mediators are TNF, IL-1, IL-6. 26- (C) The question needs you to know the function of the protease enzyme. Other viral enzymes like reverse transcriptase, integrase, etc. first get formed as a part of big polypeptide chain thats located in the core of the virus; the protease functions to break down that polypeptide to release those enzymes, thus leading to the maturation of the core. 27- (B) Struvite stones are formed in an alkaline medium, such a medium is promoted by a bacterium that has a urease enzyme which can break down the urea into ammonia and thus cause alkaline pH. The only bacterium listed that has urease enzyme is proteus. 28- (B) A patient complaining to you about his physician--> encourage the patient to communicate with the physician. 29- (B) Sensory deficit in the left hand--> a problem in the right somatosensory cortex located in the right postcentral gyrus. 30- (C) Typical adolescent gynecomastia that occurs in a large proportion of adolescents and resolves on its own in the majority of them with time. 31- (A) Progressive weakness of the proximal and distal muscles, double vision, eyelid drooping + mediastinal mass--> myasthenia gravis which is commonly associated with thymic hyperplasia/thymoma. It is caused by auto-Abs that block the A.Ch. receptors at the motor end plate. 32- (C) The pic shows severe vertebral osteoporosis with a compression fracture, the most plausible answer is IL-1 since it activates osteoclasts and is increased in postmenopausal osteoporosis which is characterized by increased resorption. 33- (E) The key sentence here is her symptoms become much more pronounced as the day progresses which is typical of MG, none of the other choices would cause that. Besides, having normal residual volume excludes the obstructive lung diseases (alpha 1-antitrypsin and chronic bronchitis). 34- (D) Nodular infiltrates + hilar adenopathy + noncaseating granulomas--> classical sarcoidosis. 35- (C) Most probably a case of metabolic syndrome, these patients have dyslipidemia which is characterized by increased triglycerides and FFAs, and decreased HDL cholesterol. 36- (C) The T4-binding substance in the blood is Thyroid binding globulin (TBG). Since Thyroid hormone is a steroid (lipid-soluble), it traverses the cell membrane and acts intracellularly on a nuclear receptor. 37- (A) Patients with Gilbert syndrome are asymptomatic, they may suffer mild jaundice in cases of stress and infection like that case, the jaundice is due to the decreased capacity of the glucuronyl-transferase enzyme, therefore the jaundice would be caused by unconjugated bilirubin. Normal liver enzymes exclude choices B and E, choices C and D should have been accompanied by other signs of anemia (C) or liver failure (D). 38- (F) One of the most dangerous infections in DM that occurs specially after DKA is mucormycosis, the fungus gains access through the cribriform plate and may spread to the orbit and the brain, it causes a necrotizing inflammation, hence the black eschar. 39- (E) A classical case of rheumatoid arthritis, the pathology involves granulomatous inflammation in the synovium of the joints, the reactive synovium forms a mass called pannus that destroys the joint and ends up in fibrosis causing the various deformities seen in RA. 40- (A) Type II error (beta error) is calculated by the equation (beta=1 power), therefore beta equals 0.2 in trial X and 0.1 in trial Y, that is, as the power increases the likelihood of the error decreases. 41- (D) In people with DM increased glucose leads to its increased conversion to sorbitol by the enzyme aldose reductase which is found in the lens, the problem with sorbitol is that it cant cross the cell membrane, so it gets trapped inside the cell, and it draws water because it is osmotically active, this leads to opacification of the lens and cataract formation. 42- (E) A classical presentation of sickle cell anemia causing acute chest syndrome which is a form of sickle cell crisis. The substitution of glutamic acid with valine in the B-chains leads to polymerization of the Hb under hypoxic conditions forming insoluble polymers, due to this the RBCs become sickle shaped and sticky and they clog the small capillaries leading to ischemia in many organs which leads to the crisis. 43- (B) The carbonic anhydrase inhibitor (acetazolamide) is of benefit in high altitude sickness because it causes acidosis, which counteracts the alkalosis caused by hyperventilation, however it is also a diuretic, and so it would cause some hypovolemia in normotensive persons which can lead to orthostatic hypotension. The only other choice that can cause orthostatic hypotension is impaired sympathetic activity, but it is unrelated to acetazolamide. 44- (B) The sequence (AATAAA) which is transcribed into (AAUAAA) is the signal required to start adenylation and formation of the poly A tail, and it is located downstream (3) of the coding region, the function of the tail is to protect the mRNA from cleavage, in its absence most of the mRNA would be broken down by the endonucleases in the nucleus. 45- (E) Classical presentation of gestational trophoblastic disease (GTD) characterized by hyperemesis gravidarum, a uterus thats large for the gestational age, and markedly increased levels of HCG. It is due to abnormal proliferation of the trophoblastic tissue. 46- (B) From the blistering diseases the one that most commonly involves the mouth is pemphigus vulgaris; it is caused by auto-Abs to the desmosomes between the keratinocytes in the stratum spinosum layer of the epidermis. 47- (B) He has multiple risk factors; being male, above 45 y/o, living alone, and having major illness. 48- (C) The IIB/IIIA receptor on platelets is the receptor that binds fibrinogen and it is essential for the process of platelet adhesion and aggregation and to strengthen the blood clot. 49- (B) Except for the glucagon receptor, all the other choices are common to both glucagon and epinephrine because both act to initiate the G-protein sequence that ends up in activating glycogen phosphorylase and breaking down glycogen. 50- (C) Tyrosine kinases is a family of enzymes that act as downstream effectors of various growth factors, they function through phosphorylating tyrosine residues on different proteins, since it is a missense mutation (i.e. it didnt lead to a premature termination of translation, so didnt affect the amount of the enzyme formed) it probably led to the formation of a non-functional enzyme that cant phosphorylate.