781. Blood flow
A. In the right coronary artery is greater in systole than diastole
B. Is increased in the cerebral circulation by hyperventilation
C. Is greater in the epicardial arteries than the subendocardial arteries at the left ventricle in diastole
D. Is lower towards the centre than the periphery oflarge vessels
E. In the left coronary artery is decreased by moderate hypoxaemia

782. Myocardial contractility is increased by all of the following except
A. Activation of adenylyl cyclase
B. Vagal stimulation
C. Digoxin
D. Mobilisation of calcium from longitudinal tubule systems
E. None of the above

783. Which of the following are true of CD4+ cells
A. Are derived from bone marrow
B. Do not have Fc receptors
C. Have class II MHC receptors
D. Can be inactivated by cyclosporin (IL 1 gene transcription inhibition)
E. Are unaffected by cytokines

784. Which is true of Haemoglobin
A. Abnormalities can lead to haemolysis in conditions such as spherocytosis and sickle cell anaemia because of increased RBC fragility
B. Haemoglobin F has a lower affinity for 2,3 DPG and thus oxygen of HbA
C. Is the major oxygen and C02 carrier
D. Colours the blood: oxygenated (red), deoxygenated (red), methaemoglobin (blue)
E. In normal venous blood, carries 6 atoms of oxygen per molecule and so is 75% saturated with oxygen

785. Which is true of blood types
A. Are determined by red cell surface agglutinogens
B. When incompatible between recipient and donor at transfusion usually result in recipient haemoagglutination
C. Can help determine parenthood, ego the child of parents who are both type B must be type B
D. Are determined by plasma agglutinins
E. Rh incompatibility between mother and foetus may necessitate intrauterine transfusion of the foetus with maternal compatible blood

786. Anticlotting mechanisms include
A. Conversion of thrombin to protein C activator
B. Antithrombin III inactivation of activated factor VIII
C. Inactivation of tissue plasminogen activator
D. Inhibition of fibrinogen degradation products by thrombin
E. Thromboxane A2, prostacyclin activity: the latter promoting vascular spasm and platelet aggregation, the former the reverse

787. Cardiac muscle usually contracts more forcefully when
A. Cell membrane NalK ATPase activity is stimulated, ego digitalis
B. Ligand gated calcium channels are opened for long periods
C. It is tetanic (individual responses fused before relaxation can occur)
D. The average sarcomere length increases
E. Adrenaline activates beta 2 receptors

788. Rhythmicity
A. Is a consequence of the plateau (phase 2 calcium in) of depolarisation at the SA node
B. Is a major feature where myocardial muscle differs from skeletal and smooth muscle
C. At the SA node is a consequence of prepotential
D. At the A V node is a consequence of sodium leak in during diastole
E. Is accelerated in the A V node by neurohumoral effects on potassium channels

789. During the ST segment of the electrocardiogram there is
A. No current flow, all myocardial membranes positive outside, negative inside
B. Normal current flow of repolarisation
C. Inability of damaged myocardium to depolarise if ST elevated
D. Current flow if other than on zero potential line
E. If elevated, current flow during diastole (TQ)

790. During the cardiac cycle
A. Systole is the’ period of ventricular contraction, ie. between the 1st and 2nd heart sounds (opening and closure of semilunar valves)
B. The stroke volume is increased by increasing the end diastolic volume, not the ejection fraction
C. Ventricular contraction commences at the ECG R wave and is not completed until the end of the T wave
D. Diastole is the period between opening and closure of the A V valves
E. Jugular venous pressure waves occur at a. atrial systole c. ventricular systole (peak of pressure) v. just prior to opening of A V valves

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