CRL Quiz 2 2008

1

A medical student on a clinical elective in East Timor develops a productive cough and fever. A chart x-ray reveals patchy right upper lobe consolidation. Which one of the following statements is correct?


  It is likely that he is immunosuppressed to develop this illness.

  It is likely that this is acute bacterial bronchitis.

  The route of infection is likely to be via the blood.

  It is likely that this is pneumonia occurring in an immunocompetent person.

  He is likely to be very hypoxaemic because most of the blood supply is to the upper lobes.


Pneumonia is a common illness and occurs in both immunocompetent and immunocompromised hosts. Immunosuppression is uncommon in this age group. Therefore the patient is most likely to be immunocompetent, and the virulence and number of organisms such that the immune system has been overwhelmed.

2

What would be the next test that you would perform?


  Arterial blood gases.

  HIV test.

  Spirometry.

  Sputum microscopy and culture.

  Measurement of serum immunoglobulins.


Sputum microscopy and culture will identify the pathogen and appropriate treatment.

3

Which one of the following statements regarding the role of surfactant is NOT CORRECT?


  It facilitates the maintenance of a dry alveolar surface.

  It lowers the pressure within alveoli.

  It facilitates the stability of the alveoli.

  It increases the surface tension of the alveoli.

  It facilitates the phagocytosis of inhaled pathogens by alveolar macrophages.


Surfactant is hydrophobic and reduces the attraction between water molecules, lowering the tendency for water to be drawn onto the alveolar surface. The reduction in water on the alveolar surface and the reduced attraction between the water molecules that remain in the presence of surfactant leads to a lowering of surface tension, which in turn lowers the pressure within the alveolus. As the pressure in each alveolus is reduced the pressure differences between adjacent alveoli are also reduced and therefore the tendency for them to empty into each other is also reduced. This feature of the surfactant action assists in the maintenance of alveolar structure. The surface tension is lowered rather than increased by surfactant. The opsonising ability of surfactant can render pathogens in the alveolar region more susceptible to phagocytosis by alveolar macrophages.

4

During primary sensitization to inhaled allergen, allergen derived peptides are presented to naïve T cells in lymph nodes by which cell type(s)?


  B lymphocytes.

  Airway smooth muscle cells.

  Lymphatic endothelial cells.

  Dendritic cells.

  Epithelial cells.


Dendritic cells traffic from the mucosa to nodes where they present antigen via upregulated MHC.

5

An effective vaccine that promoted CD4+ cell interaction with B lymphocytes as its mode of action would be expected to produce protective immunity via:


  Innate immunity.

  Mast cell degranulation.

  Macrophage apoptosis.

  Immunoglobulins.

  Soluble co-stimulation molecules.


B cells differentiation into antibody secreting plasma cells as the basis of humoral immunity.

6

Genome-wide scans of asthma susceptibility indicate that asthma:


  Is inherited as a single Mendelian trait.

  Requires inflammation to cause bronchial hyperreactivity.

  Is a complex disease involving interplay of multiple loci.

  Has no known susceptibility loci shared with COPD.

  Can be largely explained by TH2 immunity genes mapping to 5q31-3.


Multiple gene loci, each contributing a small amount individually, have been identified in genome-wide scans of asthma.

7

Afferent impulses from Slowly Adapting (Stretch) Receptors (SARS) in the lung pass in which nerve?


  Hypoglossal nerve.

  Vagus nerve.

  Spinal accessory nerve.

  Glossopharyngeal nerve.

  Facial nerve.

8

Coronary artery dominance typically relates to the origin of the:


  Right coronary artery.

  Left coronary artery.

  Anterior interventricular artery.

  Posterior interventricular artery.

  Circumflex artery.


Dominance of the coronary artery system is usually defined by which artery gives rise to the posterior interventricular artery, which supplies adjacent areas of both ventricles and the IV septum. Dominance of the right coronary artery is typical.

9

Which one of the following statements is NOT a characteristic of REM sleep?


  Rapid low voltage, mixed frequency EEG activity.

  EEG activity similar to wakefulness.

  Loss of tone in the postural muscles.

  Fast delta waves in the EEG.

  Cardiovascular instability during phasic bouts of eye movement.


In REM sleep the EEG is characterised by low voltage, mixed frequency activity. The EMG activity is very low.

10

Which one of the following structures does NOT impress upon the oesophagus producing the appearance of narrowing or constriction on a radiograph of a barium swallow?


  The arch of aorta.

  The left main bronchus.

  The arch of azygous vein.

  The diaphragmatic hiatus.


The oesophagus is a flexible muscular tube that descends from superior to posterior mediastinum passing posterior and to the right of the arch of aorta and behind the left main bronchus both of which may indent it. At the oesophageal hiatus in the diaphragm the sling-like loop of muscle also produces an indentation. These impressions slow the passage of oesophageal contents and represent sites where swallowed foreign bodies are most likely to lodge.

11

Which one of the following statements regarding the action potential of a cell in the cardiac sinoatrial (SA) node is NOT CORRECT?


  A decrease in the slope of the pacemaker potential would reduce the heart rate.

  An increase (more positive) in the threshold potential would reduce the heart rate.

  A decrease (more negative) in the starting voltage of the pacemaker potential would reduce the heart rate.

  Increased permeability to sodium is important in generating the upstroke of the SA node cell action potential.

  Increased permeability to sodium is important in repolarisation.


A is correct: A reduced slope of the pacemaker potential would increase the time taken to reach the threshold potential of the atrial pacemaker cell. Therefore, the number of beats per minute would be reduced.
B is correct: It would take longer for the pacemaker potential to reach a more positive threshold potential. Therefore, the number of beats per minute would be reduced.
C is correct: It would take longer for the pacemaker potential to move from a more negative starting voltage to the threshold potential. Therefore, the number of beats per minute would be reduced.
D is correct: The action potential depends on the pacemaker potential reaching the threshold. Therefore, the permeability of sodium (increased during the pacemaker potential) is important in “generating” the upstroke of the action potential.
E is incorrect: Repolarisation occurs as a result of increased K permeability.

12

Which one of the following statements about cardiac contraction is correct?


  Cardiac contraction requires neural activation.

  Cardiac contraction requires can be triggered during the relative refractory period of a cardiac action potential.

  Cardiac contraction depends on potassium influx into T-tubules.

  Cardiac contraction requires ADP hydrolysis by the actin filament.


A is incorrect: Cardiac contraction triggered by Action potentials generated by the pacemaker cells of the heart.
B is correct: Early after depolarisations can be triggered by influx of Ca2+ and these can trigger contractions.
C is incorrect. Ca2+ influx is through the T-tubules.
D is incorrect: ATP binds to myosin where it is hyrolysed to ADP.

13

Which one of the following statements about drugs affecting cardiac rate is correct?


  β-adrenoceptor activation slows depolarisation.

  Muscarinic receptor activation of potassium channels increases heart rate.

  Sodium channel inhibitors can trigger delayed after depolarisations in ventricular myocytes.

  Potassium channel blockers can trigger early after depolarisations in ventricular myocytes.


A is incorrect: β-adrenoceptor agonists & sympathetic activation increase rate of depolarisation.
B is incorrect: This results in a decrease in heart rate.
C is incorrect: Tend to raise threshold making after depolarisations less likely.
D is correct: By prolonging the duration of the action potential increase the possibility of an after depolarisation.

14

Which one of the following statements about the effect of cardiac glycosides in cardiac failure is correct?


  Cardiac glycosides activate β-adrenoceptors.

  Cardiac glycosides improve contractility and survival rate in patients with heart failure.

  Cardiac glycosides inhibit the activity of Na+/K+ ATPase.

  Cardiac glycosides inhibit angiotensin converting enzyme.


C is correct: There is no evidence for any action on β-adrenoceptors or angiotensin converting enzyme.
B is incorrect: While they do increase contractility, they do not necessarily improve survival rate. This is best achieved with other drugs such as ACE inhibitors that target additional mechanisms that contribute to heart failure.

15

Which one of the following statements regarding arterial haemostatic clot formation is NOT CORRECT?


  Arterial haemostatic clot formation requires stabilisation of the platelet plug.

  Arterial haemostatic clot formation is enhanced and accelerated by the actions of thrombin.

  Arterial haemostatic clot formation requires vitamin K.

  Arterial haemostatic clot formation can occur even if only platelets are present.

  Arterial haemostatic clot formation requires von Willebrands factor binding to subendothelium.


A: A platelet plug can be sufficient to stop bleeding in the microcirculation, but can be readily dislodged in an artery – stabilization of the plug by the coagulation process is required.
B: Thrombin acts to positively feedback enhancing platelet aggregation as well intrinsic pathway (factor VIII), the common pathway (factor V) and cross linking of fibrin (factor XIII).
C: Vitamin K acts to carboxylate glutamic acid residues of factors 2, 7, 9 and 10, thus enabling these factors to bind Ca++ - a necessary cofactor for biological activity.
D: See A.
E: von Willebrands factor is required for platelets to attach to the lesions via the subendothelium. Attached platelets, spread, aggregated acting as a surface on which collagulation occurs leading to a stable clot.