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- © 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- © 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- © The woman’s 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- © 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 Goodpasture’s 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- © 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 doesn’t 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) That’s 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- © The lab results show severe anemia with normal MCV (so it’s 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-popula...mpling.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- © 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- © 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 don’t 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.
