USMLE4

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USMLE4
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2015-02-01 23:50:11
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  1. Describe the presentation of Edwards syndrome.
    • Intellectual disability
    • Rocker-bottom feet
    • Micrognathia (small jaw)
    • Low set ears
    • Clenched hands with ovelapping fingers
  2. What is minute ventilation? Equation
    • VE= Tidal volume (VT) X Respiratory rate (RR)
    • Air that enters or leaves the lungs in one minute.
  3. What is alveolar ventilation? Equation?
    • VA= ( Tidal volume - Dead space) X breaths/min
    • Dead space= Tidal volume X ((PaCO2- PECO2)/ (PaCO2))
    • The volume of air that participates in gas exchange.
  4. How do we calculate physiologic dead space?
    VD= Tidal volume X ((PaCO2 -PECO2)/ (PaCO2))
  5. What is physiologic dead space?
    The volume of air that does not take part in gas exchange.
  6. What is functional residual capacity?
    • Volume of air remaining in the lungs after a normal expiration.
    • FRC= RV+ ERV
  7. What is residual volume?
    • Volume of air remaining in the lungs after forced expiration.
    • Cannot be measured by spirometry.
  8. What type of tumor is a VIPoma?
    Non-alpha, non-beta islet cell pancreatic tumor.
  9. Describe the pathophysiology and presentation of a VIPoma.
    • Persistent watery diarrhea
    • Low potassium, sodium, chloride
    • Achlorhydria- absent HCL in gastric secretions
    • PATHOPHYSIOLOGY --> VIP increases Cl- loss into stool, which causes excess loss of the accompanying H20, Na+ and K+. It also inhibits gastric H+ secretion.
  10. What produces the vasoactive intestinal peptide hormone?
    • 1. Pancreatic islet cells
    • 2. Parasympathetic ganglia in sphincters, gallbladder and intestine
  11. What is the action of VIP?
    • Relaxation of GI smooth muscle
    • Inhibition of gastric H* secretion
    • Increases pancreatic bicarbonate and Cl- secretion.
  12. How do we treat a VIPoma?
    Somatostatin
  13. What produces cholecystokinin?
    I cells (duodenum, jejunum)
  14. What is the action of Cholecystokinin?
    • 1. Increases pancreatic bicarbonate secretion.
    • 2. Increases gallbladder contraction.
    • 3. Decrease gastric emptying.
    • 4. Increase sphincter of Oddi relaxation.
  15. What is the action of secretin?
    • 1. Increase pancreatic bicarbonate secretion
    • 2. Decrease gastric secretion
    • 3. Increase bile secretion
  16. These drugs are monophosphorylated by HSV/VZV thymidine kinase to convert it to their active form.
    • Acyclovir
    • Famcyclovir
    • Valacyclovir
  17. What is the MOA of Acyclovir?
    • Monophosphorylated by thymidine kinase.
    • Inhibits viral DNA polymerase by chain termination.
  18. What is the Margination step in inflammatory leukocyte adhesion?
    • Neutrophils pushed to the periphery.
    • ↑Contact of neutrophils with endothelial lining.
  19. How do neutrophils roll?
    • Via the binding of Sialyl-Lewis X/ P-Selectin glycoprotein 1 (PSGL-1) to E-selectin and P-selectin
    • GlyCAM-1, CD34 to L-selectin
  20. What is the importance of Sialyl-Lewis X in leukocyte extravasion?
    • Margination and rolling
    • Via the binding of Sialyl-Lewis X/ P-Selectin glycoprotein 1 (PSGL-1) to E-selectin and P-selectin
  21. What is the importance of  P-Selectin glycoprotein 1 (PSGL-1) in leukocyte extravasion?
    • Margination and rolling
    • Via the binding of Sialyl-Lewis X/ P-Selectin glycoprotein 1 (PSGL-1) to E-selectin and P-selectin
  22. What is the importance of E/P/L-selectin in leukocyte extravasion?
    • Margination and rolling
    • Via the binding of Sialyl-Lewis X/ P-Selectin glycoprotein 1 (PSGL-1) to E-selectin and P-selectin.
    • GlyCAM-1, CD34 to L-selectin
  23. What is the importance of GlyCAM-1 in leukocyte extravasion?
    • Margination and rolling
    • Via the binding of Sialyl-Lewis X/ P-Selectin glycoprotein 1 (PSGL-1) to E-selectin and P-selectin.
    • GlyCAM-1, CD34 to L-selectin.
  24. What is the importance of CD34 in leukocyte extravasion?
    • Margination and rolling
    • GlyCAM-1, CD34 to L-selectin.
  25. How does tight binding occur in leukocyte extravasation?
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
    • VCAM-1 (CD106) to VLA-4 integrin
  26. What is the importance of CD54 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  27. What is the importance of ICAM-1 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  28. What is the importance of CD11 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  29. What is the importance of CD18 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  30. What is the importance of LFA-1 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  31. What is the importance of Mac-1 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  32. What is the importance of ICAM-1 in leukocyte extravasion?
    • Tight-binding
    • ICAM-1 (CD54) to CD11/18 integrins (LFA-1, Mac-1)
  33. What is the importance of VCAM-1 in leukocyte extravasion?
    • Tight binding
    • VCAM-1 (CD106) to VLA-4 integrin
  34. What is the importance of CD106 in leukocyte extravasion?
    • Tight binding
    • VCAM-1 (CD106) to VLA-4 integrin
  35. What is the importance of VLA-4 integrin in leukocyte extravasion?
    • Tight binding
    • VCAM-1 (CD106) to VLA-4 integrin
  36. What is the importance of PECAM-1 in leukocyte extravasion?
    • Transmigration/ Diapedesis
    • PECAM-1 (CD31) to PECAM-1 (CD31)
  37. What is the importance of CD31 in leukocyte extravasion?
    • Transmigration/ Diapedesis
    • PECAM-1 (CD31) to PECAM-1 (CD31)
  38. What is Diapedesis/ Transmigration in leukocyte extravasion? How does it occur?
    • Transmigration/ Diapedesis - WBCs travel between endothelial cells and exist blood cells.
    • PECAM-1 (CD31) to PECAM-1 (CD31)

  39. What is Leukocyte adhesion deficiency type 1?
    • Defect in LFA-1 (Leukocyte function associated antigen) integrin (CD18) on phagocytes.
    • Impaired Tight adhesion.
    • Absent pus formation
    • Delayed separation of umbilical cord
    • Impaired wound healing
  40. How do we calculate net filtration pressure?
    Hydrostatic pressure gradient (Pc-Pi)- (πc - πi) Oncotic pressure gradient
  41. Describe the nondisjunction seen the restriction fragment length polymorphysm analysis.
    • Maternal Meiotis I
  42. Describe the nondisjunction seen the restriction fragment length polymorphysm analysis.
    • Maternal Meiosis II
  43. Describe the nondisjunction seen the restriction fragment length polymorphysm analysis.
    • Paternal meiosis I
  44. Describe the nondisjunction seen the restriction fragment length polymorphysm analysis.
    • Paternal meiosis II
  45. Describe the pathophysiology of addison's disease.
    • Adrenal atrophy/ destruction (autoimmune, TB, metastasis)
    • Deficiency of aldosterone and cortisol production. 
    • Loss of cortisols negative feedback on pituitary leads to increased ACTH and MSH.
    • Decreased aldosterone results in ↓Na+ reabsorption, ↓K+ and H+ excretion and a compensatory ↑ in Cl- retention.
  46. What are the toxicities caused by the use of lithium?
    • Tremors, ataxia, twitching, neuromuscular agitation.
    • Polyuria (causes nephrogenic DI)
    • Ebstein anomaly
  47. Which drugs are contraindicated in the use of lithium?
    • Most Lithium is reabsorbed at PCT with Na+
    • 1. Thiazides- work in DCT and impair Na+ reabsorption. Kidney tries to compensate by ↑
    • Na+ reabsorption in PCT.
    • 2.ACE inhibitors
    • 3.NSAIDS
  48. What happens if there is a mutation in a splice site?
    • Results in the production of larger proteins (↑amino acid residues) that are nonfunctional but have preserved immune reactivity (binding to antibodies)
    • Only exons contain proper base pairs in correct order that will result in functional protein.
  49. What is the enzyme deficient in Cori disease?
    Deficiency of debranching enzyme (alpha 1,6-glucosidase)
  50. Describe the findings in Cori disease.
    • Alpha 1 -6 glucosidic branch points cannot be degraded, so small chain dextrin-like material accumulates within cytosol of hepatocytes.
    • Hypoglycemia
    • Hypertriglyceridemia
    • Ketoacidosis
    • Hepatomegaly
  51. What is the function of the Accessory nerve? Which muscles does it innervate?
    • Head turning, shoulder shrugging
    • Innervates the Sternocleidomastoid and Trapezius.
  52. Patient faints during the procedure of ear examination. What nerve causes this?
    • Vasovagal syncopial episode
    • Temporary loss of consciousness/ fainting. Results from stimulation of vagus nerve, leads to decrease in blood pressure and heart rate.
  53. This drug is used to treat this type of seizure where the ppt blanks out or stare into space.
    Absence seizures- Ethosuximide
  54. What is the MOA and use of Ethosuximide?
    • Blocks thalamic T-type Ca2+ channels
    • Absense seizures.
  55. This drug blocks T-type Ca2+ channels in the thalamus.
    Ethosuximide
  56. What is the MOA of Pheynytoin?
    • Inhibits neuronal high-frequency firing by reducing the ability of Na+ channels to recover from inactivation.
    • ↑Na+ channel inactivation.
  57. What is the MOA of Carbamazepine?
    • Inhibits neuronal high-frequency firing by reducing the ability of Na+ channels to recover from inactivation.
    • ↑Na+ channel inactivation.
  58. What is the MOA of Valproic acid?
    • Inhibits neuronal high-frequency firing by reducing the ability of Na+ channels to recover from inactivation.
    • ↑Na+ channel inactivation.
    • ↑GABA concentration by inhibiting GABA transaminase

  59. Which epilepsy drugs ↑Na+ channel inactivation?
    • Phenytoin
    • Valproic acid
    • Carbamazepine
  60. This epilepsy drug increases GABA concentration by inhibiting GABA transaminase.
    • Valproic acid
    • Vigabatrin
  61. How does large molecular weight of a drug affect its volume of distribution?
    • The drug generally remains trapped in the plasma compartment and the volume of distribution is usually low. (3-5L)
    • Large molecular weight =  Low Vd
  62. How does a drug which is bound extensively to plasma proteins affect its volume of distribution?
    • The drug remains trapped in the plasma compartment and the volume of distribution is usually low. (3-5L)
    • PLASMA protein bound = Low Vd
  63. Describe the volume of distribution in a highly charged drug.
    • Highly charged (hydrophilic) drugs generally have a low volume of distribution. (3-5L) Drug is trapped in plasma compartment.
    • Highly charged = Low Vd
  64. What is the volume of distribution in a hydrophillic drug.
    • Large molecular weight + hydrophilic = Low Vd (3-5L)
    • Small molecular weight + hydrophilic = Medium Vd (14-16L)
  65. What values indicates a low volume of distribution?
    3-5L
  66. Describe the volume of distribution of a drug which has a small molecular weight, but is hydrophilic.
    • Volume of distribution is limited to a total volume of about 14-16L (plasma volume + interstitial volume).
    • Small molecules + Hydrophilic = Medium Vd
  67. Describe the volume of distribution of a drug which has a small molecular weight and is also uncharged (hydrophobic).
    • The drug can cross cell membranes and reach intracellular compartment.
    • These drugs have the highest volume of distribution. (41L)
    • Small molecular weight + Hydrophobic = High Vd
  68. Drugs that are advidly bound in the tissues (bound to tissue protein)
    • Drugs accumulate readily within cells, thereby maintaining low plasma concentrations.
    • They have the highest volume of distribution (41L).
    • TISSUE protein bound = High Vd
  69. What value indicates a medium volume of distribution?
    14-16L
  70. Describe the volume of distribution of a drug which has a small molecular weight and is lipophilic.
    • The drug can cross cell membranes and reach intracellular compartment.
    • These drugs have the highest volume of distribution. (41L)
    • Small molecular weight + Lipophilic = High Vd
  71. Which type of drugs has a low volume of distribution?
    • Large molecular weight 
    • Charged molecules (HYDROPHILIC)
    • Bound to PLASMA proteins
    • 3-5L
  72. Which type of drugs has a medium volume of distribution?
    • Small molecular weight and is hydrophilic
    • 14-16L
  73. Which type of drugs has a high volume of distribution?
    • Small molecular weight + Lipophilic / Hydrophobic
    • Bound to TISSUE protein
    • 41L
  74. What is the function of T-tubules in muscle contraction?
    • Transmit a depolarizaton signal from the sarcolemma to the sarcoplasmic reticulum in a rapid and uniform manner.
    • They have a large number of voltage-gated Ca2+ channels (Dihydropyridine receptors), coupled to Ryanodine receptors (Ca2+ release channels) on the S.R. 
    • Activated dihydropyridine receptors on the T-tubules activate ryanodine receptors on the S.R which leads to release of Ca2+ from the S.R and induction of muscle contraction.
  75. A lack of T-tubules in muscle fibrils leads to?
    • Uncordinated muscle contractions.
    • The uniform distribution of T-tubules in skeletal muscle fibers ensures that a depolarizing signal reaches each fiber at the same time.
    • A lack of T-tubule would lead to uncordinated contraction of individual fibers.
  76. What is the function of troponin C in muscle contraction? An abnormality of it leads to?
    • Ca2+ released from the S.R bind to Troponin C, causing a movement of tropomyosin to reveal the myosin-binding sites on actin.
    • An abnormality of troponin C or mysoin would lead to absence of contraction in response to release of Ca2+.

  77. What causes myasthenia gravis?
    • Autoantibodies to Postsynaptic Acetylcholine receptor.
    • Poor contractile force on repeated stimulation.
  78. What trinucleotide expansion is seen in myotonic dystrophy?
    CTG
  79. What causes myotonic dystophy type 1?
    • CTG trinucleotide  repeat expansion in the DMPK (dystrophia myotonica protein kinase) gene.
    • Leads to abnormal expression of MYOTONIN PROTEIN KINASE
    • Impaired relaxation after a single contraction.
  80. Abnormal expression of myotonin protein kinase is characteristic of which disease?
    • Myotonic dystrophy - CTG
    • Impaired relaxation after a single contraction.
  81. How are cardiac myocytes electrically coupled to each other?
    By gap junctions
  82. How do osteocytes remain connected to each other?
    By Gap junctions
  83. What are zona occludens?
    • Tight junctions - two closely adherent cytoplasmic membranes without an intervening space.
    • Prevents paracellular movement of soultes.
    • Composed of claudins and occludins.
  84. What are tight junctions? What is its function?
    • Zona occludens
    • - two closely adherent cytoplasmic membranes without an intervening space.
    • Prevents paracellular movement of soultes.
    • Composed of claudins and occludins.
  85. What are claudins?
    Component of Tight junctions 
  86. What are occludins?
    Component of Tight junctions 
  87. What is the function of hemidesmosomes?
    Connects keratin in basal cells to the underlying basal membrane.
  88. What is the zonula adherens?
    • Actin filaments/ actin cytoskeleton connect with CADherins (Ca2+-dependent adhesion proteins) to hold the cell together.
    • Loss of E-cadherin promotes metastasis
  89. What are Cadherins?
    Ca2+-dependent adhesion proteins which connect with actin filaments/ actin cytoskeleton to hold the cell together.
  90. What is the macula adherens?
    • Desmosome
    • —structural support via keratin interactions. .
  91. What are desmosomes? Function?
    Desmosome (macula adherens)—structural support via keratin interactions.
  92. What causes this condition?
    • Winged scapula
    • Due to Lesion of long thoracic nerve
    • Can be caused by axillary node dissection after mastectomy or stab wounds.
    • Deficient Serratus anterior
    • Cannot abduct arm above horizontal position.
  93. What is the function of the Serratus anterior muscle? What happens if this muscle is deficient?
    • It anchors the scapula into the thoracic cage.
    • Functions to abduct arm above horizontal position.
  94. Injury to the long thoracic nerve results in? What causes this injury?
    • Winged scapula
    • Axillary node dissection after mastectomy, stab wounds
    • Affects Serratus anterior- can't abduct arm over horizontal position.
  95. An abnormality is seen in the back when a patient is asked to face a wall and push against it with both hands.
    Winged scapula.
  96. Charcot-Leyden crystals
    • Found in people that have allergic diseases such as asthma or parasytic infections.
    • Contain eosinophil membrane protein
  97. What is the function of IL-3?
    Growth and differentiation of bone marrow stem cells.
  98. What is the function of IL-5?
    • Enhances class switching to IgA.
    • Growth and differentiation of eosinophils.
  99. This interleukin enhances growth and differentiation of eosinophils.
    IL-5
  100. What is the major component of pulmonary surfactant?
    Dipalmytoyl phosphatidylcholine
  101. When are the fetal lungs considered to be mature?
    Lecithin (phosphatidylcholine) to sphingomyelin ratio is greater than 2.
  102. Salmon-colored rose spots on abdomen are characteristic of?
    Salmonella typhi
  103. How does Salmonella penetrate the gut mucosa?
    Via transporters on enterocytes and via phagocytosis by M cells in Peyers patches.

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