USMLE13

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USMLE13
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2015-01-19 13:49:59
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  1. This drug is used to treat this type of seizure where the ppt blanks out or stare into space.
    Absence seizures- Ethosuximide
  2. What is the MOA and use of Ethosuximide?
    • Blocks thalamic T-type Ca2+ channels
    • Absense seizures.
  3. This drug blocks T-type Ca2+ channels in the thalamus.
    Ethosuximide
  4. 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.
  5. 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.
  6. 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

  7. Which epilepsy drugs ↑Na+ channel inactivation?
    • Phenytoin
    • Valproic acid
    • Carbamazepine
  8. This epilepsy drug increases GABA concentration by inhibiting GABA transaminase.
    • Valproic acid
    • Vigabatrin
  9. 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
  10. 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
  11. 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
  12. 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)
  13. What values indicates a low volume of distribution?
    3-5L
  14. 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
  15. 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
  16. 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
  17. What value indicates a medium volume of distribution?
    14-16L
  18. 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
  19. Which type of drugs has a low volume of distribution?
    • Large molecular weight 
    • Charged molecules (HYDROPHILIC)
    • Bound to PLASMA proteins
    • 3-5L
  20. Which type of drugs has a medium volume of distribution?
    • Small molecular weight and is hydrophilic
    • 14-16L
  21. Which type of drugs has a high volume of distribution?
    • Small molecular weight + Lipophilic / Hydrophobic
    • Bound to TISSUE protein
    • 41L
  22. 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.
  23. 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.
  24. 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+.

  25. What causes myasthenia gravis?
    • Autoantibodies to Postsynaptic Acetylcholine receptor.
    • Poor contractile force on repeated stimulation.
  26. What trinucleotide expansion is seen in myotonic dystrophy?
    CTG
  27. 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.
  28. Abnormal expression of myotonin protein kinase is characteristic of which disease?
    • Myotonic dystrophy - CTG
    • Impaired relaxation after a single contraction.
  29. How are cardiac myocytes electrically coupled to each other?
    By gap junctions
  30. How do osteocytes remain connected to each other?
    By Gap junctions
  31. 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.
  32. 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.
  33. What are claudins?
    Component of Tight junctions 
  34. What are occludins?
    Component of Tight junctions 
  35. What is the function of hemidesmosomes?
    Connects keratin in basal cells to the underlying basal membrane.
  36. 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
  37. What are Cadherins?
    Ca2+-dependent adhesion proteins which connect with actin filaments/ actin cytoskeleton to hold the cell together.
  38. What is the macula adherens?
    • Desmosome
    • —structural support via keratin interactions. .
  39. What are desmosomes? Function?
    Desmosome (macula adherens)—structural support via keratin interactions.
  40. 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.
  41. 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.
  42. 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.
  43. 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.
  44. Charcot-Leyden crystals
    • Found in people that have allergic diseases such as asthma or parasytic infections.
    • Contain eosinophil membrane protein
  45. What is the function of IL-3?
    Growth and differentiation of bone marrow stem cells.
  46. What is the function of IL-5?
    • Enhances class switching to IgA.
    • Growth and differentiation of eosinophils.
  47. This interleukin enhances growth and differentiation of eosinophils.
    IL-5
  48. What is the major component of pulmonary surfactant?
    Dipalmytoyl phosphatidylcholine
  49. When are the fetal lungs considered to be mature?
    Lecithin (phosphatidylcholine) to sphingomyelin ratio is greater than 2.

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